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Swinburne University of Technology
Sarawak Campus
School of Engineering and Sciences
Mechanical Properties of Kenaf Fibre Reinforced Urea
Formaldehyde Resin Composites
Masters of Engineering
(Mechanical)
Tay Chen Chiang
February 2013
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ABSTRACT
Composite materials, in general, are used in the industry because of their positive
qualities such as optimized performance, minimized weight and volume, cost effectiveness,
chemical and biodegradation resistance. The main purpose of this research is to find the
best particleboard by using low cost materials. The research in this thesis is focused on
kenaf fibre with adhesive of low emission Urea Formaldehyde resin with 51.6% solid
content. The fabrication process for UF fibres boards is based on wood particle that makes
the fabrication simple and economical. Boards with the densities of 500kg/m3 and 600kg/m3
were chosen based on the standard wood particleboards. Kenaf fibres of two different sizes
and various fibre weight fractions (90wt%, 85wt%, 80wt%, 75wt% and 70wt %) were used
in the fabrication of kenaf UF composite boards. The specimens were subjected to different
mechanical tests such as impact test, internal bonding test, screw test, bending test, tensile
test and water absorption test. The fabrication of the particleboards was done using hot
press for 6 minutes under the pressure of 40 Ton at 180°C for different fibres weight
fractions with different sieving sizes of fibres and densities. The results demonstrates that
the samples with higher density yields the higher value of modulus of rupture, modulus of
elasticity, tensile strength, Young’s modulus, screw test, impact test and internal bonding.
The findings also demonstrate that the level of density affects the performance of a board,
where the board with low density will result in low mechanical strength as compared to the
boards with higher density. Types of raw materials and phenol formaldehyde resin were
also investigated through different tests to identify the properties of the fabricated boards.
The obtained results show that the higher tensile and bending strength values were achieved
at 80wt% regardless of the fibres size. Besides, the results shows that the highest values for
modulus of rupture MOR and modulus of elasticity MOE for 1mm and 0.6mm fibres size
were achieved at 80wt%. While the optimum impact strength was founded to be at 85wt%
for 1mm fibres size and at 80wt% for 0.6mm. Screw and internal bonding tests show that
80wt% at 1mm fibres size provides the highest value among other possible options.
.
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ACKNOWLEDGEMENTS
First of all, I would like to express my deepest gratitude to my superior, Dr. Saad A.
Mutasher ( School of Engineering and Sciences ) together with Madam Ekhlas Aboud
Osman and for their patience, unfailing enthusiasm, firm guidance, support and time which
have contributed throughout the research period and ensuring this study successfully done.
I would like to acknowledge sincere thanks to my second supervisor, Professor
Nazim Mir-Nasiri ( School of Engineering and Sciences ) for supporting in this project, Mr.
Pee Yaw and the staff of Sarawak Forestry Company, for sparing their time, sharing some
information and demonstrating the fabrication process of the particleboard.
Further appreciation goes to Ms. Ivy Bong, R&D/QC manager of Hexzachem
Sarawak Sdn. Bhd. For providing few bottles of Urea Formaldehyde, her advises and
assistance.
Lastly, I would like to express my appreciation to those who have given me either
direct or indirect assistance in this project.
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DECLARATION
We hereby declare that this report entitled “Mechanical properties of Kenaf fibre
reinforced urea formaldehyde resin composites” is the result of my own project work
except for quotation and citations which have been duly acknowledged. We also declare
that is it has not been previously or concurrently submitted for any other master at
Swinburne University of Technology ( Sarawak Campus).
Name : Tay Chen Chiang Signature:
ID : 4198964
Date :
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Tables of Contents
ABSTRACT ........................................................................................................................... 2
ACKNOWLEDGEMENTS ................................................................................................... 3
DECLARATION ................................................................................................................... 4
List of Tables........................................................................................................................ 16
List of Abbreviations............................................................................................................ 17
CHAPTER 1 ........................................................................................................................ 19
Introduction .......................................................................................................................... 19
1.1 General .................................................................................................................. 19
1.2 Objectives .............................................................................................................. 21
CHAPTER 2 ........................................................................................................................ 22
Literatures Review ............................................................................................................... 22
2.1 Introduction ........................................................................................................... 22
2.2 Natural Fibres ........................................................................................................ 22
2.3 Physical and Mechanical Properties of Fibres ...................................................... 25
2.4 Advantages and Disadvantages of Natural Fibre .................................................. 26
2.5 Kenaf Fibre ............................................................................................................ 27
2.5.1 Bast Fibre ....................................................................................................... 28
2.5.2 Core Fibre ...................................................................................................... 28
2.6 Waste wood ........................................................................................................... 28
2.7 Matrices ................................................................................................................. 31
2.8 Urea Formaldehyde (UF) ......................................................................................... 32
6
2.9 NH4CI .................................................................................................................... 32
2.10 Processing Method for particleboards ............................................................... 33
2.12 Factors Affecting the Mechanical Properties of the Particleboards .................. 36
2.12.1 Density ........................................................................................................... 36
2.12.2 Fibre weight fraction ...................................................................................... 38
2.12.3 Moisture and Durability ................................................................................. 43
2.12.4 Surface Wet ability and Buffering ................................................................. 45
2.12.5 Particle Size for board fabrication.................................................................. 46
2.12.6 Hybrid Composite .......................................................................................... 50
2.12.7 Resin types ..................................................................................................... 54
CHAPTER 3 ........................................................................................................................ 58
Experimental programme ..................................................................................................... 58
3.1 Introduction ........................................................................................................... 58
3.2 Outline of the experimental programme ............................................................... 58
3.3 Materials ................................................................................................................ 59
• Kenaf core fibres ................................................................................................... 59
• Waste wood ........................................................................................................... 60
• Urea Formaldehyde ............................................................................................... 61
• NH4CI .................................................................................................................... 62
3.4 Manufacturing Apparatus ...................................................................................... 62
• Mixer & Spray ....................................................................................................... 62
• Mould / Silicon glass map/ Steel plate/ Steel bar .................................................. 64
• Hot Press ................................................................................................................ 64
7
3.5 Manufacturing Procedure ...................................................................................... 66
3.5.1 Process flow chart .......................................................................................... 66
3.5.2 Calculation for the particleboard .................................................................... 67
3.5.3 Particleboard Fabrication Process .................................................................. 68
3.6 Specimens Preparation .......................................................................................... 72
3.6.1 Test standards ................................................................................................. 72
• Flexural/Bending test: ........................................................................................... 73
• Tensile Test ........................................................................................................... 75
• Internal Bonding .................................................................................................... 76
• Screw Test ............................................................................................................. 77
• Impact Test ............................................................................................................ 78
3.6.2 Physical Test .................................................................................................. 78
• Water Absorption and Thickness Swelling ........................................................... 78
• Water absorption (%) ............................................................................................ 79
• Thickness swelling (%) ......................................................................................... 79
3.7 Moisture for the Raw Materials ............................................................................. 80
3.8 Density Profile ....................................................................................................... 80
CHAPTER 4 ........................................................................................................................ 82
Results & Discussion ........................................................................................................... 82
4.1 Introduction ........................................................................................................... 82
4.2 Fibre Properties ..................................................................................................... 82
4.2.1 Fibre Size ....................................................................................................... 82
• Fibre Length .......................................................................................................... 82
8
• Fibre Diameter ....................................................................................................... 84
4.2.2 Moisture Content ............................................................................................ 86
4.3 Density Profile of Particleboards .......................................................................... 87
4.4 Mechanical Properties of Particleboards ............................................................... 89
4.4.1 Tensile Properties ........................................................................................... 90
• Tensile Stress vs Strain .......................................................................................... 90
• Effect of Density ................................................................................................... 91
• Effect of the Size ................................................................................................... 94
• Effect of Weight Fraction at Different Types of Fiber and sizes .......................... 96
• Effect of Matrix ................................................................................................... 100
• Effect of Hybrid ................................................................................................... 102
4.4.2 Bending Properties ....................................................................................... 105
• Effect of Density ................................................................................................. 105
• Effect of the Size with 75% wt of Kenaf Core Ffibre ......................................... 107
• Effect of Different Fibre at Different Weight Fraction and Sizes ....................... 109
• Effect of Matrix ................................................................................................... 113
• Effect of Hybrid ................................................................................................... 116
4.4.3 Internal Bonding........................................................................................... 120
• Effect of Density ................................................................................................. 120
• Effect of the Size with 75wt% ............................................................................. 121
• Effect of Different Fibre at Different Weight Fraction and Sizes ....................... 122
• Effect of Matrix ................................................................................................... 125
• Effect of Hybrid ................................................................................................... 126
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4.4.4 Screw Test .................................................................................................... 128
• Effect of Density ................................................................................................. 128
• Effect of the Size with 75wt% ............................................................................. 129
• Effect of Different Fibre at Different Weight Fraction and Ssizes ..................... 130
• Effect of Matrix ................................................................................................... 132
• Effect of Hybrid ................................................................................................... 133
4.4.5 Impact Strength ............................................................................................ 135
• Effect of Density ................................................................................................. 135
• Effect of the Size with 75wt% ............................................................................. 136
• Effect of Different Fibre at Different Weight Fraction and sizes ........................ 137
• Effect of Matrix ................................................................................................... 139
• Effect of Hybrid ................................................................................................... 140
4.5 Physical Test on Particleboards ........................................................................... 142
4.5.1 Thickness Swelling TS ................................................................................. 142
• Effect of Density ................................................................................................. 142
• Effect of the Size with 75wt% ............................................................................. 143
• Effect of Different Fibre with different weight fraction and Sizes ..................... 143
• Effect of Matrix ................................................................................................... 146
• Effect of Hybrid ................................................................................................... 146
4.5.2 Water Absorption ......................................................................................... 148
• Effect of Density ................................................................................................. 148
• Effect of the Size with 75wt% ............................................................................. 149
• Effect of Different Fibre with different weight fraction and Ssizes .................... 150
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• Effect of Matrix ................................................................................................... 153
• Effect of Hybrid ................................................................................................... 154
CHAPTER 5 ...................................................................................................................... 156
Conclusions and recommendations .................................................................................... 156
5.1 General ................................................................................................................ 156
5.2 Physical properties of natural fibres .................................................................... 156
5.3 Physical properties of the particleboard .............................................................. 156
5.4 Mechanical properties of the particleboard ......................................................... 157
5.5 Recommendations for future studies ................................................................... 158
References .......................................................................................................................... 159
Appendix ............................................................................................................................ 169
A.1 Real life Application : .......................................................................................... 169
A.2 Calculation: ............................................................................................................. 171
A.3 Result without Dimensionless: ................................................................................ 171
Published Paper .................................................................................................................. 174
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List of Figures
Figure 2.1: Categories of natural fibres (Mokhtar et al. 2007) ............................................ 23
Figure 2.2 : Various types of natural fibres (Moktar et al. 2007) ....................................... 24
Figure 2.3 : Flexural strength of kenaf bast and core fibre reinforced UP composites (Ishak et al, 2010) ............................................................................................................................ 41
Figure 3.1 : Kenaf core fibres .............................................................................................. 59
Figure 3.2 : Kenaf bast fibres ............................................................................................... 60
Figure 3.3 : 0.4mm sieving size of waste wood ................................................................... 60
Figure 3.4 : 1mm sieving size of waste wood ...................................................................... 61
Figure 3.5 : Mixing drum ..................................................................................................... 63
Figure 3.6 : Container with spray gun .................................................................................. 63
Figure 3.7 : Mould, Silicon glass map, Steel plate .............................................................. 64
Figure 3.8 : Kobayashi Hot Press ......................................................................................... 65
Figure 3.9: Panel Saw SZIII Figure 3.10 : Chamber .................................................... 65
Figure 3.11 : Process Chart .................................................................................................. 66
Figure 3.12 : Dried the particles in the oven ........................................................................ 69
Figure 3.13:Weighting raw material .................................................................................. 69
Figure 3. 14 : UF preparation ............................................................................................... 69
Figure 3. 15 : NH4CI preparation ........................................................................................ 69
Figure 3.16 : Resin is reloaded ............................................................................................. 70
Figure 3.17 : Raw materials in the drum .............................................................................. 70
Figure 3.18 : Drum rotated at a constant speed .................................................................... 70
Figure 3.19 : The dried mixture was collected ..................................................................... 70
Figure 3.20 : The dried mixture was weighed...................................................................... 70
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Figure 3.21 : Level up the particles Figure 3.22 : Even mixing Figure 3.23 : Manually compress ............................................................................................................................... 71
Figure 3.24:Transferring the particleboard Figure 3.25 : Particleboard for hot press process .................................................................................................................................. 71
Figure 3.26 : Particleboard begging compress Figure 3.27 : Released heat ...... 72
Figure 3.28 : Cutting process Figure 3.29 : Curing process .......................... 72
Figure 3.30 :Cutting diagram of particleboard specimens for testing (mm) ........................ 73
Figure 3. 31: Flexural test with three-point loading ............................................................. 74
Figure 3.32 : Test apparatus of tensile test ........................................................................... 75
Figure 3.33 : Detail of tensile a test specimen’s dimensions (mm) ..................................... 76
Figure 3.34 : Test apparatus for internal bonding ................................................................ 77
Figure 3.35 : Screw test Figure 3.36 : Screw test specimen ........................................... 78
Figure 3.37 : Water absorption and Thickness Swelling test ...................................................
Figure 3.38 : Oven Figure 3.39 : Heating process Figure 3.40 : Weighing .... 80
Figure 3.41: x-ray (VDP) ..................................................................................................... 81
Figure 4.1: Length of kenaf core fibre with 1mm and 0.6mm sieving size ......................... 83
Figure 4.2 : Length of kenaf bast fibre ................................................................................. 84
Figure 4.3: Length of waste wood with 1mm sieving size .................................................. 84
Figure 4.4: Diameter of kenaf core fibre 0.6mm and 1mm sieving size .............................. 85
Figure 4.5: Diameter of Bast ................................................................................................ 85
Figure 4.6 : Diameter of waste wood ................................................................................... 86
Figure 4.7: The Round Vibratory Sieves (Unit Test) and (b) The Sieves with Different Size of kenaf Fibre (Osman et al. 2010) ................................................................................... 86
Figure 4. 8: Density Profile Vs Thickness ........................................................................... 88
13
Figure 4. 9: Density Profile Vs Thickness (U, M and Consistent Shape) ............................ 89
Figure 4.10: Tensile stress vs strain at different weight fraction of kenaf core fibre using different size ........................................................................................................................ 91
Figure 4.11: Dimensionless tensile strength at different weight fraction of kenaf core fibre using different densities ....................................................................................................... 92
Figure 4.12: Dimensionless young’s modulus at different weight fraction of kenaf core fibre using different densities .............................................................................................. 94
Figure 4. 13: Dimensionless tensile strength of kenaf core fibre at different sizes ............. 95
Figure 4. 14 : Dimensionless young’s modulus of kenaf core fibre at different sizes ......... 96
Figure 4. 15: Dimensionless tensile strength at different types of fibres ............................. 98
Figure 4.16: Dimensionless young’s modulus at different types of fibres ........................ 100
Figure 4. 17 : Dimensionless tensile strength at different resin ......................................... 101
Figure 4. 18 : Dimensionless young’s modulus at different resin .................................... 102
Figure 4.19 : Dimensionless tensile strength of hybrid fibres ........................................... 103
Figure 4.20: Dimensionless Young’s modulus of hybrid fibres ........................................ 104
Figure 4. 21: Tensile test .................................................................................................... 105
Figure 4.22: Bar chart of dimensionless bending strength at different weight fraction of kenaf core fiber using different densities ........................................................................... 106
Figure 4.23: Dimensionless MOE at different weight fraction of kenaf core fibres using different densities ............................................................................................................... 107
Figure 4.24: Different size of kenaf core fibres with 75% weight fraction ....................... 108
Figure 4. 25: Dimensionless MOE at different size of kenaf core fibres with 75 (wt%)... 109
Figure 4.26: Dimensionless of bending strength at different types of fibres with different fibres weight fraction ......................................................................................................... 111
Figure 4.27 : Different types of fibres on MOE ................................................................. 113
Figure 4.28: Comparison between UF and PF ................................................................... 115
14
Figure 4.29: Dimensionless MOE affected by the UF and PF ........................................... 116
Figure 4.30: Dimensionless bending strength on the hybrid particleboard with 1mm /0.6mm sieving size for core with 1mm waste wood ...................................................................... 118
Figure 4.31: Dimensionless MOE effected by hybrid 1mm/0.6mm sieving size with 1mm waste wood ......................................................................................................................... 119
Figure 4.32: Bending specimen , bending process and the fail specimen after the test. .... 119
Figure 4.33: Dimensionless internal bonding at different weight fraction of kenaf core fibres using different densities ........................................................................................... 121
Figure 4.34: Dimensionless internal bonding at different sizes of kenaf core fibres ......... 122
Figure 4.35: Different types of fibres affected on internal bonding .................................. 125
Figure 4. 36: Dimensionless Internal bonding affected by resin ....................................... 126
Figure 4. 37: Dimensionless internal bonding affected by hybrid ..................................... 127
Figure 4.38: Internal Bonding Test and the specimen fail at the middle ........................... 128
Figure 4.39: Dimensionless screw test at different weight fraction of kenaf core fibres using different densities ..................................................................................................... 129
Figure 4.40: Dimensionless Screw Test at different size of kenaf core fibres ................... 130
Figure 4.41: Different types of fibres affected on screw test ............................................. 132
Figure 4.42: Dimensionless screw test affected by resin ................................................... 133
Figure 4.43 Dimensionless screw test affected at hybrid ................................................... 134
Figure 4.44:Dimensionless impact test at different weight fraction of kenaf core fibres at different densities ............................................................................................................... 136
Figure 4.45: Dimensionless impact strength at different size of knead core fiber ............. 137
Figure 4.46: Dimensionless impact strength at different type of fibres ............................. 139
Figure 4.47: Dimensionless impact strength at different resin Effect of Hybrid ............... 140
Figure 4.48: Dimensionless impact strength at hybrid ...................................................... 141
Figure 4.49: Impact test and the fail specimen .................................................................. 141
15
Figure 4.50: Thickness swelling affected by density ......................................................... 142
Figure 4.51: Thickness swelling affected by the different size of kenaf core fibres with 75wt% ................................................................................................................................ 143
Figure 4.52: Thickness swelling affected by kenaf core fibres with different weight fraction and sizes ............................................................................................................................. 145
Figure 4.53: Thickness swelling affected by bast and waste wood with different weight fraction ............................................................................................................................... 145
Figure 4.54: Thickness swelling affected at different resin ............................................... 146
Figure 4.55: Thickness swelling of hybrid composites ...................................................... 147
Figure 4.56: Thickness swelling process and the output.................................................... 148
Figure 4.57: Water absorption affected by density ............................................................ 149
Figure 4.58: Water absorption affected at different size of kenaf core fibres.................... 150
Figure 4.59: Water absorption affected at kenaf core fibres ............................................. 152
Figure 4.60:Water absorption affected at waste wood and bast........................................ 153
Figure 4.61: Water absorption affected by kenaf core fibres and bast............................... 154
Figure 4.62: Water absorption affected by hybrid ............................................................. 155
Figure 4.63: Water absorption test ..................................................................................... 155
Figure A. 1: Prototype of the particleboard ....................................................................... 170
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List of Tables
Table 2.1: Physical properties of the plant fibre (Mwaikambo et al. 2006)......................... 24
Table 2.2 : Chemical composition, moisture content and microfibrillar angle of vegetable fibres (Taj et al. 2007) .......................................................................................................... 25
Table 2. 3 : Dimensions of selected natural fibres (Craig et al. 2005) ................................. 26
Table 2.4: Mechanical properties of selected organic and inorganic fibres ......................... 26
Table 2. 5: Advantages and disadvantages of natural fibres ................................................ 27
Table 3.1: Analysis of UF ................................................................................................... 61
Table 3.2 : Analysis Data for PF .......................................................................................... 62
Table 3.3 : Properties of NH4CI ........................................................................................... 62
Table 4.1: Moisture content of the natural fibres ................................................................. 87
Table A.1 Particleboard application .............................................................................. 169
Table A. 2: General use and grades ................................................................................... 170
Table A.3 : Actual value for the tests ................................................................................. 171
17
List of Abbreviations
MOR = Modulus of Rupture
MOE = Modulus of Elasticity
IB = Internal Bonding
SW = Screw Withdrawal
L/D = length/diameter
TS = Thickness Swelling
UF = Urea Formaldehyde
PF = Phenol Formaldehyde
NH4CI = Ammonium Chloride
MDI = Methylene diphenyldiisocyanate
WA = Water Absorption
RLDPE = Recycled Low Density Polyethylene
MC = Moisture Content
KBFB = Kenaf Bast Fabre Bundles
VDP = Vertical Density Profile
σf = MOR
ΔW= Increment in load (N)
ΔS=deflection with the load
F max= breaking load (N)
Wi = initial weight
Ww= wet weight
Ti = initial thickness
Tw = wet thickness
E = modulus (MPa)
d = density (N/m3)
T = thickness (m)
J = impact strength (kJ/m2)
A = area ( m2 )
F = force (N)
V = volume ( m3 )
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CHAPTER 1
Introduction
1.1 General
Many researchers show interest in the benefits of composite technology. Some of
the composite materials that show high mechanical and thermal properties are widely used
in various applications such as aerospace and sports equipment. The use of composite
materials raised many environmental issues that need to be handled effectively.
Environmental friendly composites, where natural fibres are normally used as
reinforcements combined with polymers such as unsaturated polyester, urea formaldehyde
and epoxy as matrices, are created by researchers as a mean of overcoming these problems.
The interest in using natural fibres in composites has increased in the recent years because
of their optimized performance, minimized weight and volume, cost effectiveness,
chemical and biodegradation resistance properties. The main objective of using natural
fibres in composites is to reduce the cost and increase the performance characteristics. New
class of composite materials should be explored because of their potentials in various
applications and also as a substitute for wood-based material applications.
As demand for wood-based panels increase, but facing environmental issues such as
deforestation and forest degradation, countries like Malaysia and Pakistan need to turn to
better and effective solutions to meet the demand of the industries and at the same time
protect the natural resources. Due to the shortage of raw materials, industries in Iran are
forced to use lignocelluloses materials from different sources to substitute wood as the raw
material for production. One of the most effective ways to meet the demand for wood is by
creating more plantations that focus on fast-growing tree species to replace wood as raw
material and at the same time, decrease the demand on natural forest and protect natural
resources.
Kenaf, known as Hibiscus Cannabininus, a common tropical and sub-tropical wild
plant found in Africa and Asia, is now widely cultivated for its commercial potentials. The
20
kenaf grows around 4 meters within 4 to 5 months and requires minimal time of care. It
takes only 150 days to mature before it is ready for harvesting (Palil et al. 2008). Kenaf
plant has a single, straight and branchless stalk that is made up of an inner woody core and
an outer fibrous bark surrounding the core. The outer, coarser fibres, is called bast fibres
and the inner, finer fibres, is called core fibres. Kenaf can be used in making hardboards,
medium-density fibreboards, environmental mats, paper, ropes and engineered wood.
Kenaf normally goes through chemical treatment to improve the mechanical properties
before processed as composite materials. Kenaf can absorb nitrogen and phosphorus in the
soil and accumulate carbon dioxide at high rate.
Kenaf is part of the lignocelluloses fibres that requires lower processing
temperature, about 2000C and can only use higher temperatures for short periods during the
fabrication process. Jamal et al. (2010) explained that kenaf requires low processing
temperature and incompatibility between the hydrophilic natural fibres and hydrophobic
polymer. This is because of the limitation provided by the lignocelluloses fibres and caused
the limitation of thermoplastic and thermosetting resin to be used.
Effective waste management is a prevailing issue even though we live in an
advanced era. Environmentally friendly products are often ignored and this creates waste
management problems in many parts of the world. During the manufacturing process, a lot
of particles and wood powder are produced and are generally disposed through burning. By
reprocessing of these residuals, we can convert waste into useful resources and alleviate the
increasing pressures on landfill sites. Presently, scientists are trying to convert these wastes
into useful resources, such as particleboards, and also as a mean of solving the shortage of
forest resources. The better utilization of wastes, such as wood powder, will also benefit the
furniture industry as an additional income.
For this research, urea-formaldehyde was chosen as composite matrix. Urea-
formaldehyde is a non-transparent thermosetting resin or plastic, which were made by the
combination of urea and formaldehyde heated with the ammonia or pyridine. These resins
are used as adhesive resins in the particleboard industries due to their high reactivity, good
21
performance and low cost. Urea-formaldehyde resins have properties such as high tensile
strength, flexural modulus and heat distortion temperature, low water absorption, mould
shrinkage, high surface hardness, elongation at break and higher stability. Results from a
survey by Conner et al. (1996), show that more than 70% of urea-formaldehyde resin is
used in forest industry products, for examples, particleboards (61%), hardwood plywood
(5%) and medium density fibreboards (27%). Due to its useful properties, urea-
formaldehyde is applied in the manufacturing process to produce products such as
decorative laminates, textiles, paper, foundry sand molds, wrinkle resistant fabrics, cotton
blends, rayon and corduroy. It is also used to glue wood together.
1.2 Objectives
The objectives of this study are as follow:
1. Use different natural fibres and thermosetting to manufacture the
composites.
2. Study the physical properties such as, density and moisture content of
composites at different parameters.
3. Study the mechanical properties such as, tensile, flexural, internal bonding,
screw and impact of composites at different parameters.
4. Specified the optimal composite materials using different natural fibres.
5. Study the physical and mechanical properties for hybrid composites at
different parameters.
22
CHAPTER 2
Literatures Review
2.1 Introduction
As demand for wood-based products (such as plywood, oriented strand boards,
hardboards, particleboards and fibreboards) increased substantially worldwide, wood-based
industry in some countries including Malaysia are heading towards a looming shortage of
wood. As the demand for particleboards in the furniture sector and interior decoration
continues to rise, manufacturers find it difficult to fulfil the demand due to a significant
increase in the price of wood, resin and energy (Nourbakhsh, 2010). The fact that the world
is facing a shortage in wood supply due to deforestation and forest degradation is forcing
the industry to find effective and sustainable replacements for wood. Countries with limited
natural forests, studies have been carried out on wide range of fibres as an alternative for
wood (Nourbakhsh, 2010) and the results of these studies revealed that fast growing
species, such as kenaf, that can be harvested two times annually and with minimum care,
are the answer in solving the above mentioned problem.
2.2 Natural Fibres
In the composite industry, cellulosic fibres are derived from many renewable
resources that are cost effective and possess positive properties, such as low density and
high stiffness, for reinforcement of thermoplastics (Maya et al. 2003). Fibres can be divided
into two major types: natural fibre and synthetic fibre. Currently, the use of different types
of natural fibres, such as flax, hemp, jute straw, wood, rice husk, wheat, barley, oats, rye,
cane, grass, reeds, kenaf and pineapple leaf, in the plastic industry are being explored
(Bledzki et al. 1999). Natural reinforced polymers resulted from combining natural fibres
with the selected matrix. Natural fibres are used as a component of composite materials to
make products such as paper or felt.
The use of synthetic fibres in polymer composites is fading because they are
expensive and non-biodegradable. They pollute the environment and are limited in
23
advanced applications. Natural fibres, like kenaf, pineapple leaf, banana leaf fibres and rice
stalk fibres, on the other hand, are cheap and environmentally friendly. They are available
in large quantity and possess limitless possibility of their utilization for various
applications. Natural fibres can be classified into wood fibres and non-wood fibres as
shown in the Figure 2.1. This research focuses on the core and bast of kenaf fibres which is
a type of non-wood fibre.
Figure 2.1: Categories of natural fibres (Mokhtar et al. 2007)
The physical properties of various plant fibres are shown in the Table 2.1. The
properties of bio-fibres are dependent on the source itself, plant conditions (such as the
climatic factor), harvesting age and separating techniques (Singha et al. 2009).
24
Table 2.1: Physical properties of the plant fibre (Mwaikambo et al. 2006)
Nowadays, natural fibres, as shown in the Figure 2.2, like flax, hemp, kenaf, jute,
henequen, and coir are normally used and extensive studies were done on those fibres
(Moktar et al. 2007).
Figure 2.2 : Various types of natural fibres (Moktar et al. 2007)
A study conducted by Taj et al. (2007) on chemical composition and mechanical
properties of natural fibres showed that different types of fibres have different percentage
of cellulose, hemicelluloses, lignin, pectin, moisture content, waxes and microfibrillar
angle. Craig et al. (2005) reported that cellulose shows the least variation in chemical
25
structure and can be considered as the major framework of a fibre. It is a highly crystalline,
linear polymer of hydro-glucose molecules with a degree of polymerization and provides
strength, stiffness and structural stability. Lignin is an amorphous, cross-linked polymer
network consisting of an irregular of variously bonded hydroxyl and methoxy-substituted
phenyl propane units and acts as a chemical adhesive within and between fibres. Pectin are
complex polysaccharides, consist of modified polymer, chains are cross-linked by calcium
ions and improve structural integrity in pectin-rich areas. Basically, the chemical and
structural composition, fibre type and growth conditions significantly influenced the
mechanical properties of a fibre.
Table 2.2 : Chemical composition, moisture content and microfibrillar angle of vegetable fibres (Taj et
al. 2007)
2.3 Physical and Mechanical Properties of Fibres
Craig et al. (2005) stated that the physical and mechanical performance of fibres are
affected by the types of species, natural variability within species, differences in diameter
and growing seasons. Table 2.3 and 2.4 illustrate the different physical dimensions and
mechanical properties of various fibres.
26
Table 2. 3 : Dimensions of selected natural fibres (Craig et al. 2005)
Table 2.4: Mechanical properties of selected organic and inorganic fibres
2.4 Advantages and Disadvantages of Natural Fibre
As shown in Table 2.5, there are advantages and disadvantages of using natural fibres
in the composite industry. Plants fibres are known for being cost-effective in terms of price
and production, however, the viability of applying them in the composite industry has to be
investigated carefully to ensure that the advantages far outweigh the disadvantages. Inferior
27
composites with poor properties could be created if the natural fibres are not selected
properly. The composites could inherit poor properties due to the incompatibility between
hydrophilic natural fibres and hydrophobic polymer matrix (Ismail et al. 2011), and these
composites will likely produce undesirable results in the mechanical tests such as bending
test, internal bonding test, tensile test and screw test.
Table 2. 5: Advantages and disadvantages of natural fibres
Advantages Disadvantages
Natural fibres have low density and
decreasing environmental pressures
Low investment
Low specific weight which result in higher
specific strength and stiffness
It is a renewable resource, production requires
little energy
Natural fibres have low thermal stability,
degradable and release volatile components
Lower durability, fibre treatment needed for
better performance
High moisture absorption which causes
swelling of the fibres
Lower strength properties
Price can fluctuate based on harvest results
or agricultural politics
2.5 Kenaf Fibre
Kenaf is a member of hibiscus family that is biodegradable, non-toxic and
environmentally friendly (Taj et al. 2007). It is used to make clothing, toys and shoes in the
current market. A study done by Shinji Ochi et al. (2008) show that different growth
conditions can affect the length of the kenaf fibres. Fibres grown under the average
temperature of 30oC have greater tensile strength and elastic modulus than those under the
28
average temperature of 22oC. Kenaf plant consists of two parts: the outer part is called bast
and the inner part is called core.
2.5.1 Bast Fibre
Bast fibres are able to provide better strength in the final composite materials if they
are arranged parallel to each other (Paridah et al. 2009). Boards made from 100% bast
fibres have poor performance due to inferior bond strength caused by wetting of fibres. The
bending strength can be increased by applying 50% of bast in the middle of the
particleboards.
Kenaf bast fibres have higher aspect ratio (L/D) than rubber wood and core fibre,
thus, they are able to resist deformation due to the large bonding area. 100% bast fibre
boards have the lowest performance due to low bonding strength that is caused by lack a of
fibre wetting. Slender particles would result in higher bending strength than the less slender
particles. Longer and thinner strands or particles will give higher MOR and IB values than
shorter and thicker strands. Particleboards made from kenaf bast would have higher
bending strength than those made from kenaf core or rubber wood. This is because bast
fibres tend to cling together and form bundles that may influence the homogeneity of a
kenaf board (Juliana. 2011). Jacob et al. (2009) mentioned that bast fibres are expected to
provide stiffness and toughness characteristics to balance the properties of bio-composites.
2.5.2 Core Fibre
Kenaf core is very light; hence, more particles are needed per volume and it can be
compacted easily without blowing problem during the fabrication. Kenaf core fibres have
superior properties in both stiffness and strength; irrespective of the adhesive used. Kenaf
core is also very absorbent. However, it can be improved by using adhesives, such as
phenol resin, to improve the thickness swelling (Pariadah et al. 2009).
2.6 Waste wood
In the composite industries, scientists need to consider the new composites under
the wet condition before applying them in the real life applications. Chen et al. (2005)
29
stated that the dimensional stability of the nonwoven composites under the wet condition
will be the main issue to consider in the auto interior application because automobiles are
required to endure severe weather conditions such as heavy raining or snowing.
Yasin et al. (2010) stated that wood has been the major source for particleboards
and fibreboards. Particleboards are manufactured from wood by using binders such as
conventional formaldehyde. Camelia et al. (2009) found out that the mechanical behaviour
of carpinus wood flour/ UF resin composites were slightly better than the corresponding
composite materials that were filled with beech wood flour. Carpinus wood flour composite
has greater stiffness compared to beech wood flour. However, both composites possess low
mechanical characteristics in bending and therefore, are only used to manufacture products
that are not categorised as strong products in the furniture or building construction.
Rubber wood had much superior mechanical properties than kenaf core fibres when
converted into particleboards. This could be attributed to the fact that rubber wood has
higher density than core fibres, thus producing higher strength and better wet ability for
bonding (Juliana, 2011). Reinforcement by using small wood chips with high-density
polyethylene exhibited poorer impact loading due to the rubbing of large wood chips
against one another that produced interference forces and restricted their sliding in matrix.
As the result, higher concentration of large wood chips can resist impact fracture better
compared to small wood chips. Impact strength could be lowered due to the interaction
between the neighbouring fibres in the composite that appeared to constrain the matrix flow
and resulted in the embrittlement of the matrix (Wong, 2010).
According to Dukarska et al. (2010) stated that, irrespective of the type of the
lignocelluloses materials and adhesive resin, the strength of board will increase with an
increase in resonation rate. An increase in the resin PMDI from 5%-8% will lead to an
increase in the rigidity of particleboards. In their study, it was found that there was no
increase in the internal bonding because the less porous surface of evening primrose straw
compared to wood chips hindered the penetration of adhesive resin into the straw particles.
Consequently, the binding of the core layers became weaker and the strength of the board
30
was decreased. The type of the lignocelluloses materials used in the manufacturing process
as well as the type and amount of the binding agent influence the ability of a board to resist
water. Evening primrose straw /PMDI showed decreasing swelling value because free
spaces had been reduced during the compression process and water penetration was also
reduced when the specimen was soaked in water.
Chaharmahali et al. (2008) reported that the flexural modulus increased when the
fibre content of wood plastic composites was increased up to 70% and it the decreased as
the fibre content reached 80%. When the fibre content was increased from 70 to 80%, no
sufficient adhesive bonding was present to achieve higher modulus; causing the composites
to bend easily under the load. As there was no compatibilizer used in preparing the panels,
the flexural strength of the composites decreased due to the lack of compatibility between
the phases of the fibre content. In the wood plastic composites, plastic are utilized as an
adhesive for bonding wood particles/fibres together. Wood plastic composites have higher
capacity of the screws compared to the medium density fibreboards and the particleboards
because the thermoplastic will conform around the thread of a screw and allows the load to
transfer effectively along the thread. Higher fibre contents show lower impact strength due
to the lack of compatibility between the composite components.
An experiment conducted by Grigoriou et al. (2000) found that industrial wood
chips particleboards showed better mechanical properties compared with the kenaf core
chipboards. Ayrilmis et al. (2009) explained that wood flakes possess high strength and
elastic modulus but lower impact strength and poor water resistance. The MOR of the
particleboards is strongly influenced by the properties, volume ratio and interaction of the
constituent materials. However, bending and stiffness properties are highly correlated with
the geometry of the wood flakes.
Yaser et al. (2010) stated that when the composites were immersed in water for 2
hours, the value of water absorption for recycled composite particleboards, recycled
medium density fibreboards and the hybrid between particles and medium density
fibreboards increased from 60% to 80% of fibre content because the hydrophilic property
31
of natural fibres was increased. In addition, the water absorption capacity increased as well
when the immersion time was increased. High moisture absorption could cause dimensional
change and affect the mechanical properties (Ismail et al. 2011). When the fibres loading
was increased, the water uptake also increased with immersion time because free OH
groups of lignocelluloses fibres came into contact with water through hydrogen bonding
which resulted in water uptake and weight gain in composites. Tabarsa et al. (2011)
mentioned that cellulosic materials have poor absorption resistance because of the polar
group that attracts water molecules through hydrogen bonding. This phenomenon causes
moisture build-up in the fibre cell wall and fibre-adhesive interface. In their experiment, it
was found that the TS properties improved when the pressing time was increased. The fine
particles had filled up the pores between the coarse particles in the core layer and resulted
in better TS value. Consequently, the contact between the fine particles and blended
particles had increased. In addition, the fine particles had low amount of woody cells and
they absorb less water than thick particles.
2.7 Matrices
The role of a matrix is to transfer stress between the fibres, provide a barrier against
an adverse environment and protect the surface of fibres from mechanical abrasion.
Polymer matrices are divided into two categories: thermosetting and thermoplastics.
Thermoset like urea formaldehyde, epoxies and phenolics have highly cross-linked
structure and are hard. They do not soften when heated. Thermoplastic like high density
polyethene, low density polyethene, poly vinyl chloride, on the other hand, can be heated
from solid state to a viscous liquid and then cooled back down to solid. The heating and
cooling process can be applied multiple times without degrading the polymer properties.
The adhesive that fills the lumens of vessels at the bonding line will directly
influence the depth of penetration (Ivana Gavrilovic et al. 2008). The distribution of
vessels is uniformed within the annual rings and the penetration of adhesive into the ray
cells is omitted due to the presented cells content in their lumens. In the inter-phase region,
adhesive penetration could be expressed by the partly filled or fully filled anatomical
vessels of wood tissues.
32
2.8 Urea Formaldehyde (UF)
UF resins are used as a major adhesive in wood based products due to their
advantages such as cost-effective, ease to use under a wide variety of curing condition, low
curing temperature, water solubility and resistance to microorganism and to abrasion,
hardness and excellent thermal properties (Kamal et al. 2009). The gelation time of the
resin is important to ensure sufficient hot pressing time for particleboard during the
fabrication. Insufficient hot pressing may cause adverse effects to the panels produced.
Urea-formaldehyde (UF) is a non-transparent thermosetting resin or plastic, made
from urea and formaldehyde, heated in the presence of a mild base such as ammonia or
pyridine. Urea formaldehyde is a cost-effective and widely used in the wood product
industry. These resins are used in adhesives, finishes and moulded objects. Urea-
formaldehyde has high tensile strength, flexural modulus and heat distortion temperature,
low water absorption, mould shrinkage, high surface hardness, elongation at break, and
volume resistance.
Bonding quality between natural fibres and the polymer matrix play an important role
in the composite industry. Most of the manufacturers are using UF as their bonding agent.
UF is conventionally employed in manufacturing composite products. One of the major
concerns on the composite products is water solubility. Water soluble of urea formaldehyde
is chemically incompatible with natural fibres like straw materials because it will reduce
bonding quality (Yasin et al. 2010). Bonding quality is very important because it affects the
whole composite material. The optimum performance of the selected binders will be
between 5-15% when employed in the final composite. The mechanical properties of
composite materials using urea formaldehyde are found to be higher compared to using
urea formaldehyde resins alone (Singha et al. 2009). Four minutes of hot press process will
result in lower formaldehyde emission if compared to two minutes (Hse et al. 2008).
2.9 NH4CI
Ammonium chloride is an inorganic compound with the formula NH4Cl is added
into the UF resin during the mixing process, it will accelerate the curing process. Kim et al.
33
(2009) further explained that when the polymerization process starts, the molecules will be
polymerized through cross linking, and as a result, the mechanical properties are strengthen
with good thermal properties as well as high chemical and corrosion resistance. The length
of the curing time will basically affect the strength of the final product, cost and production
time. An experiment conducted by Hse et al. (2008) on the use of acid and alkaline
catalysts in increasing internal bonding shows that the internal bonding (IB) of a board is
increased when the former was used. The experiment shows that the IB increased while the
gel time decreased. This can be correlated to the curing speed of resin with the pressing
condition. Faster curing speed leads to a higher degree of curing completion and better
bonding strength and reduces formaldehyde emissions.
2.10 Processing Method for particleboards
Compression fabrication technical is used to fabricate the particleboards.
Different process parameters are used to produce board with good mechanical properties. A
research done by Ghalehno et al. (2011) used roselle, a type of natural fibre, to produce
particleboards where the dried chips were classified into fine and coarse sizes with two
different ratios of 30:70 and 40:60. The composites were hand-formed and hot pressed at
1350C, 1500C and 1650C for 6 minutes by using maximum pressure of 30kg-2. Shibata et al.
(2006), in their research used bamboo and kenaf fibres composites that were fabricated at
0.5g/cm3 and the 18 fibre layers were heated for 6 minutes.
Mohan kumar et al. (2008), in a research, focused on the fabrication technique to
produce particleboards. The short area fibre reinforced PF composites was fabricated by
using hydraulic hot press at a temperature of 1400C with a pressure of 2MPa for 16
minutes. Bharath et al. (2009) conducted a research on areca fibres and maize powder,
added with urea formaldehyde and using hydraulic hot press at temperature of 1400C with a
pressure of 2MPa for 30 minutes.
Kasim et al. (2001) fabricated single-layer and three-layer particleboards with
12mm and 340mm x340mm thickness. The board was designed with three density levels
(561, 641 and 721 kg/m3) and mixed with 8, 10, 12% of resins. The particleboards were
34
pre-pressed at 3.5MPa for 30 seconds and then followed by a 6 minutes pressing at 160oC
with the pressure set at 120kg/cm2. In another research, Jani et al. (2010), produced a
single-layer low density particleboard by using kenaf core fibres and three different types
of resins; urea formaldehyde, phenol formaldehyde and methyl phenyl methane di-
isocyanate. In the research, UF resin at solid content of 64% and PF at 51% functioned as a
wood binder. 1mm to 2mm of the particle size were mixed with the UF at volume fraction
of 8%, 10% and 12% during the fabrication process. Kenaf particles were manually
blended with adhesives to form a mat in a mould and pre-pressed in cold press at 35kg/cm2
and subsequently pressed in hot press at 170oC for 6 minutes.
Chew et al. (1998) fabricated single-layer and three-layer particleboards by adding
urea formaldehyde to yemane. The flake and fine yemane were sprayed into a wooden
mould and then pre-pressed at 3.5kg/cm2. The pressing process was done with a hydraulic
press machine and the temperature was maintained at 1600 C for 8 minutes. Another
research done on rice husk flour by Young-Kyu Lee et al. (2003) with peak pressure of 25
kgf/cm2 and the temperature of 1400C for 6 minutes.
2.11 Board Fabrication Problem
During the hot pressing process, the panel could blow up when the press is opened
because the internal steam pressure is greater than internal bonding strength. At the same
time, two moisture gradients will exist in the particleboard; one is increasing moisture
content from the hot surfaces to the core and the other is decreasing moisture content from
the middle of mat to the edge. Steam pressure and rate of steam escaping from the edges of
a particleboard are influenced by process variables such as press temperature, mat porosity
and moisture content, density, press closing speed and resin characteristics; therefore, these
variables need to be considered during the fabrication of a board. Blowing problem can be
reduced by slightly opening the press in order to the target thickness to relieve steam
pressure. The longer duration of the burp will delay the time for the internal steam pressure
to reach its maximum value. However, particleboards of bigger size will require more
relieve time during the press time. (Cai et al. 2009)
35
Chew et al. (1998) stated that particleboards with a density around 700kg/m3 are
prone to blowing problems due to the interaction between the mat moisture content, board
and particle density during the hot pressing process. Small amount of particles in the raw
material will decrease in specific density resulting in smaller openings for steam flow
within the particle mat during hot pressing. Consequently, this will lead to a build-up of
steam within the board and blowing as steam is not sufficiently vented out from the board.
A research done by Xu et al. (2005) on manufacturing method affecting the
mechanical properties of kenaf/methylene diphenyldiisocyanate composites showed that
high density (0.55g/cm3) composites made by one-step pressing method experienced de-
lamination condition due to high compaction ratio that made it difficult for the steam inside
the board to escape. The MDI adhesive, basically, formed a film on the surface of the board
and prevented the steam from escaping; therefore, causing the pressure in the board to
become higher than the bonding strength.
Another factor contributing to the low strength of kenaf core particleboards is the
distribution of the employed resin. During the mixing process, the binder did not cover the
entire surface of the particles but rather just stayed on the surface of the core particles in the
form of small droplets. Uneven distribution will form a weak joint, and upon loading, the
force will easily break at the weakest point (Juliana, 2011).
Ghalehno et al. (2011) stated that when the press temperature is increased, the
bending strength, internal bond strength and thickness swelling of the panels are also
improved because the bond between the particles is strengthen and the resin efficiency is
hardened during the hot pressing process. Hse et al. (2008) further explained that longer
pressing time will significantly lower thickness swell and water absorption. Moreover,
panels bonded with acid catalysed resin will give lower TS and WA results compared to
alkaline catalysed resin.
A study done by Xue et al. (2008) on the effect of temperature and loading rate on
tensile properties showed that tensile strength increased gradually as the loading rate
increased due to the concerned elastic modulus. Kenaf bast fibre bundles (KBFB) were
36
failing because of unexpected residual stresses due to the uneven resin drying. Free
elongation in KBFB was attributed to the complete loss of integrity after the conditioning
(1700 C and 1800 C for 24 hours) and which consequently caused degradation process.
When the moisture content of KBFB was reduced to zero, the tensile modulus showed
slight increase (about 5%) after high temperature treatment induced brittleness and failure
in strength reduction.
Papadopoulos et al. (2006) mentioned that by applying higher temperature the
internal bonding (IB) will be improved. The core of mattress is always at the lowest
temperature if compared to the surface. In addition to improved plasticization of wood and
the properties, an increase in the temperature will likely lead to an increase in the cross-
linking and curing of the resin.
2.12 Factors Affecting the Mechanical Properties of the Particleboards
2.12.1 Density
Density of a material can be defined as mass per unit volume or in another term;
specific gravity. A particleboard is divided into three categories based on the level of
density: low density (density range of below 0.59g/cm3), medium density (density range of
between 0.45 and 0.8g/cm3), and high density board (density range of greater than
0.8g/cm3) (Yasin et al. 2010).
Normally, the outcomes of a particleboard fabrication will not achieve the target
density. Pariadah et al. (2009) explained that a particleboard is 4% higher than the target
density. Idris et al. (2011) further explained that density profile is influenced by the particle
configuration, moisture distribution in the mat, hot press temperature and the rate of
closing, resin reactivity and the compressive strength of the particles. An experiment on
kenaf core board (Seale et al. 1996) affirmed that the actual density of a material is
influenced by the particular size of the material, the binder and applied pressures.
The results of an experiment done by Kasim et al. (2001) show that higher
compaction ratio at high density can increase the strength properties of a material.
37
However, increasing the density will lead to a higher thickness swelling, since a higher
compressive set exists and stresses are relieved.
A particleboard of high density level is usually associated of having high strength
properties because of the high compaction ratio applied during the fabrication process. Idris
et al. (2011) found that by increasing the density of a board, the thickness swelling (TS) and
water absorption (WA) values decreased due to low porosity and difficult diffusion on the
high board density. The swelling occurred due to the presence of hygroscopic particles and
the release of compression stresses of the particleboard. Wood adhesive joint strength
decreases with wood density above 0.7-0.8g/cm3 because dense wood tends to have low
porosity and this makes it difficult for adhesive to penetrate into it (Cheng et al. 2005).
Basically, insufficient penetration or over penetration will reduce the bonding strength.
The results of a study done by Jani et al. (2010) on the development of low density
particleboard, by using kenaf core fibres at three targeted density levels; 350 kg/m³, 450
kg/m³ and 550 kg/m³ and using three types of resins namely; urea formaldehyde, phenol
formaldehyde and methyl phenylmethane di-isocyanate, show that density level has a
significant effect on the performance of a board. Low density boards (350 kg/m³) have
lower mechanical strength compared to boards with higher density (450 kg/m³ and 550
kg/m³). When the density of a particleboard is increased, the internal bonding strength
values are improved due to better adhesive binding between the binder and fibres; thus,
resulting in greater ability to withstand the perpendicular forces.
Density is affected by the loss of fine particles during the consolidation in the hot
press process (Rafael et al. 2009). Teresa et al. (2011) explained that TS values increase as
the density of a board decreases.
Xu et al. (2005) further explained that when density is increased, the MOR value
and tensile strength are also increased due to the higher strength value of the kenaf bast
fibre-woven sheet compared to kenaf core particleboard. The MOR value between a
composite panel and single-layer binder less particleboard is decreased when the density of
a board is increased. Thickness swelling value is increased when the density of a board is
38
increased in one-step and two-step process; two-step process resulted in higher TS value
because of the overlaying surface layer and larger spring back.
MOR value increased when the board density is increased because MOR depends
on the bonding strength between fibres, individual fibre strength, and fibre geometry.
Additionally, a low MOR could also be attributed to the length/diameter (short or long)
rations of the fibres (Xu et al. 2006).
An experiment conducted by Xu et al. (2006) showed that IB increased when the
board density was increased because the high steam pressure and long cooking time during
the fabrication resulted in the degradation of chemical components. Tabarsa et al. (2011)
stated that boards made with bagasse particles have higher IB than those made from polar
and mixed hardwood particle because this may be due to the high compaction of bagasse
furnish which has faster heat transfer to the core layer and resulted in more cured resins.
The results of an experiment conducted by Dai et al. (2004) show that lower core density
can cause problems in internal bonding strength. The permeability decreases dramatically
when the mat density is increased because the mat will became denser and reduced the
voids formed between the particles.
Cai et al. (2002), shows that wood specific gravity is statistically correlated to screw
withdrawal strength and screw diameter. The screw withdrawal was affected by many
factors such as screw geometry, depth of penetration into wood, wood grain direction,
moisture content, species and rate of loading.
2.12.2 Fibre weight fraction
As part of the investigation, the mechanical properties of the final particleboard
were affected by the fibres weight fraction. Sufficiency matrix is needed to bond the
particles in order to have a good bonding between the particles and matrix.
The results of an experiment conducted by Nishino et al. (2003) to investigate the
effects of kenaf fibre content on Young’ modulus and the tensile strength of kenaf/PLLA
composite show that the Young’ modulus increased when the fibre content was increased
39
up to 70% in volume. Tensile strength, on the other hand, decreased when the fibre content
was increased. The decrease in the mechanical properties of the composite with fibre
content above 70% volume was due to the insufficient filling of the matrix resin.
Kenaf/PLLA composites with 70% volume contributed to the maximum value for Young’s
modulus and tensile strength compared to those of the matrix resin because of the effective
integration between the kenaf fibres and the matrix.
The matrix resin was incorporated into the interfibrilar region and, as a result, good
stress was transferred from the matrix into the kenaf fibres. Kenaf/PLLA composites
showed high level of anisotropy that led to unidirectional high mechanical performance but
the quasi-isotropic laminated composites showed an almost similar modular in all
directions.
Ishak et al. (2010) stated that composites with 20% of fibre content for both kenaf
bast and core showed the highest tensile strength. Both fibres showed significant decrease
in the elongation due to lower elongation break of kenaf fibres. The poor interfacial
bonding between the fibres and matrix was due to insufficient matrix in wetting the fibres.
Zampaloni et al. (2006) conducted a research on kenaf-polypropylene natural fibres
composites fabrication. Based on the research, it is found that both 30% and 40% fibre
contents provided enough reinforcement to increase the strength of the polypropylene
powder. Additionally, 3% of epolene couping agent was added to increase the fibre-matrix
adhesion.
Jani et al. (2010) found out that an increase in resin content resulted in higher MOE;
irrespective of the level of density and resin type due to the inherent stiffness of kenaf
particles. A study done by Grigoriou et al. (2000) found that kenaf fibre boards exhibited
better bending strength than industrial wood chip and Kenaf fibre boards with 12% of UF
exhibited better bending strength than the 10% of UF.
Shibata et al. (2006) explained that when the fibre volume fraction is increased up
to 60%, the flexural value will first increase, and then it will decrease due to insufficient
resins to wet the fibres. 43% of fibre volume fraction showed the highest value for flexural
40
modulus. Flexural modulus at the maximum level will decrease the specific gravities in the
porous composite. The flexural modulus in the kenaf porous composites was higher than
bamboo composites because the fibres are effective when the matrix covered the entire
surface of the fibres. An experiment conducted by Ismail et al. (2011) showed that flexural
strength and modulus will increase when the filler loading is increased because higher filler
loading requires higher deformation stress.
The value of MOR decreased when the rise husk flour content and was increased
and so did wood-based composites. Particleboards made from UF resin with the higher
solid content had showed higher value than particleboard made from UF resin with lower
solid content (Lee et al. 2003). Kasim et al. (2001) mentioned that an increase in the resin
content will result in improved mechanical properties (such as strength and dimensional
stability) because more bonding sites are made available.
Penetration of adhesive such as UF into the porous network of wood cells leads to
better bonding strength (Xing et al. 2005). However, excessive penetration may waste the
adhesive and lead to a starved bonding, with insufficient adhesive remaining at the interface
and low resin bonding efficiency. Resin solution may penetrate and diffuse into the fibres
easily because of the wet and hot conditions during the blow line blending process.
Sometimes, resin penetration may be neutralised due to the presence of moisture inside the
fibres that spreads from the interior of the fibre to its surface during the drying process.
Fracture toughness of a composite is affected by interlaminar, interfacial strength parameter
(Zhong et al. 2007). However the impact strength is influenced by the factors such as
matrix fracture, fibre-matrix de-bonding and fibre pull out. A decrease in toughness leaves
a composite with significantly low impact strength. The superior strength of a composite
may be associated with proper interfacial adhesion between the fibres and matrix with
reasonable amounts and can act as a stress transferring medium. Figure 2.3 shows that
unsaturated polyester/ kenaf composites with the fiber content of 10% showed the optimal
values for highest flexural strength (Ishak et al.2010).
41
Figure 2.3 : Flexural strength of kenaf bast and core fibre reinforced UP composites (Ishak et al, 2010)
An experiment conducted by Mirbagheri et al. (2010) showed that un-notched
impact strength value decreased when the fibre content was increased. Kenaf bast fibre
composites with 10 wt% and core composites with 5wt% obtained the highest impact
strength. The fibres acted as a stress transferring medium and were able to absorb impact
energy effectively. The applied stress could be transferred more effectively due to an
increase in the total contact of fibre surface; thus enhancing the stress transfer across the
fibre/ matrix interface at high strength fibres. (Wong 2010).
Screw withdrawal value can be improved by increasing the resin content and
density of a particleboard (Chew et al. 1998). Jani et al. (2010) explained further that better
screw withdrawal strength can be improved either by increasing the wood content or using
higher resin dosage. Internal Bonding strength can be improved with higher resin loading
and higher board density. In addition, better adhesive binding between the binder and fibres
resulted in a greater ability to withstand the perpendicular forces (Jani et al. 2010).
When resin with high mobility is dropped on the wood surface, the resin will spread
out spontaneously without any external forces. The high mobility will cause considerable
depth penetration into the compressed particles and resulted in their total impregnation and
42
may repair the weak zones by bonding them together. Halligan et al. (1974) mentioned that
the level of resin affects the internal bonding strength of a composite. Efficiency in resin
spread and good curing on the surface flakes will promote better bonding strength. On the
other hand, the core of the panel usually has lower density which is the weaker layer and
will fail as the failure zone. Halligan et al. (1974) mentioned that at higher moisture
contents, low density/high resin boards possess the highest bonding strength. Elongation at
break will be reduce if the fibre loading is increased because the fibre loading in the matrix
will result in composites becoming stiffer and harder and reduce the composite’s resilience
and toughness (Maya et al. 2003).
UF bonded wood composite products are not water resistant, so water absorbing
capacity and thickness swell are increased (Clause et al. 2000). Kamal et al. (2009)
explained that the higher amount of raw materials used in making a composite will increase
the amount of water absorption. When the weight fraction increases, the water absorption
will also increase because of the insufficiency of matrix to bind the raw materials. Water
absorption decreased when the resin contents were decreased due to the presence of more
resins in the board when the density increased. In addition, chemical reactions resulting
from cross-linking in hydroxyl groups are found in kenaf and resin (Jani et al. 2010).
Thickness swelling can be improved by increasing the resin content and board
density (Chew at al. 1998). Xu et al. (2006) stated that thickness swelling increases when
the density of a board is increased as a result of high degree of spring back. Furthermore, an
increase in steam pressure and cooking time will lead to an increase in thickness swelling
due to Poisson effect; where an increase in thickness restrains movement in the lateral
direction. When the resin content was increased, the thickness swelling of the board
decreased as resin incorporated into the board made the wood more repellent to water (Jani
et al. 2010; Muehi et al. 2003). A.N. Papadopoulos et al. (2002) explained that thickness
swelling can be reduced by adding 0.5-1% of wax to the boards bonded with 6 and 8%
resin respectively. Combination of higher dosage rate and wax is an alternative that can be
used to reduce thickness swelling.
43
By applying additional recycled low density polyethylene (RLDPE) on the water
melon particles, the Young’s modulus had increased due to the presence of polar group in
RLDPE or water melon particle surface; the mechanism will strengthen the RLDPE/water
melon particle interface and hold them together and increase the resistance to deformation
(Idris et al. 2011). Uniform particle distribution has efficiently hindered the chain
movement during the deformation process. The impact strength and impact energy had
increased due to the presence of particles in RLDPE resin that led to better bonding
between the particles and resin. Papadopoulos et al. (2006) mentioned that superior
performance of a resin is related to its high mobility on wood surface.
2.12.3 Moisture and Durability
Moisture content plays a significant role in a board composition pressing process
because it aids in plasticising the fibres and accelerates heat transfer into the mat core,
decreases the melting point of lignin and creates better contacts between the fibres. Craig
et al. (2005) explained that moisture content depends on the type of fibres. In composite
materials, natural fibres absorb less moisture in the final composite process due to the
encapsulation by polymer matrix. Moisture content is able to plasticise the fibres and alters
the composites’ performance. To reduce the moisture content, scientist disperse and
encapsulate the fibres in matrix during the compounding process; thus, limiting fibre
content, improving fibre-matrix bonding, chemically modifying the fibres and protect the
composite from moisture exposure. Additionally, it promotes the formation of hydrogen
bonding and lignin bonding between the fibres (Xu et al. 2006). Kasim et al. (2001)
mentioned that the moisture content of chips can be reduced by oven-drying them at 600C.
Moisture content has a great influence on the mechanical properties, such as
bending and shear stiffness. The results of a study done by Arne et al. (2011) show the
stiffness of cross-laminated timber panels made from softwood properties dropped with an
increase in the moisture content within the hygroscopic range. The modulus of elasticity
(MOE) in grain direction of defect free timber dropped to approximately 1.5% when the
wood moisture is increased by 1%. Swelling in the middle lamellas did not influence the
MOE but cracks would be formed along the grain. Shear modules are responsive to the
44
changing of wood moisture, crack formation and swelling. Shear modules will drop with an
increase in moisture and increase when moisture is reduced.
Moisture content has a significant influence on the quality of the particleboards
because higher moisture content could limit the application due to weaker stability at high
humidity (Zhong et al. 2005). When a composite is exposed to moisture, the hydrophilic of
kenaf fibre swells and as a result, micro cracking of the thermosetting occurs on its (Rashdi,
2009). Halligan et al. (1974) mentioned that the strength reduction is particularly noticeable
in moisture ranging between 10-15 %. Hence, as the moisture content increases, the MOR
of boards with higher resin content decreases at a slower rate than lower resin boards. In
addition to moisture content, the particle geometry, resin content, specific gravity and
moisture levels also have great influence on the MOR.
Papadopoulos et al. (2006) reported that 7% of the MC could attribute to better
wood glue interface because there was sufficient water to harden the UF molecules but the
wood was not plasticized sufficiently for the maximum number of bonds to be formed, as
evidenced by the failure of IB samples. Plasticization of wood normally occurs when the
wood is heated at 1800; however, low pressing time is a limited factor. Higher MC content
will reduce the glue bonding formation because the water molecules act as a competitor in
the formation of hydrogen bonds between the UF resin and the wood chips.
Hybrid composites have lower moisture content due to the hybrid arrangement that
reduces the absorption of moisture into the composite and possess denser arrangement of
fibres that fill up the voids during the fabrication process. The hygroscopic nature of
lignocelluloses fibre mat materials will absorb the moisture from the surrounding (Jawaid,
2011). The MOR and MOE could be increased by pressing time and the moisture content of
the mat. This is to make sure sufficient of heat to transfer into the core section. Higher mat
moisture gradient between the face and core layer had improved the heat transfer and
resulted in better mechanical properties. Using light species can also improve the
mechanical properties of wood composites because of the high compaction ratio (Tabarsa et
al. 2011).
45
Nemli et al. (2007) reported that an optimal moisture content of the mat should be
around 9% to 13% to improve the MOR and MOE because during the hot pressing process,
moist particles can be closely pressed under temperature and pressure; humidity will cause
a tight structure on the surface. If the moisture content of the particles is around 17%, the
MOR and MOE values will decrease because steam bubbles will appear on the surface
layer and destroy the adhesive linkages. Moisture content has negative effects on the
internal bond and thickness swelling because the moisture cannot evaporate from the mat at
higher moisture content and it weakens the contact between the core layer particles, thus,
creating pores between the particles that increase the water absorption value.
In addition, particles with low moisture content decrease the mechanical properties
of particleboards because they absorb more adhesive. Consequently, there is not enough
adhesive on the particle surfaces and the excessive drying may lead to surface deactivation
and resulted in what is known as poor adhesion phenomena. Moisture content must be
ranging between 1-5%, depending on the adhesive system, because the residual moisture is
converted to stem in the press; if too much steam is generated when the press is open, the
affected board will delaminate due to the sudden release of steam pressure. In short, the
presence of sufficient moisture content in the particles is vital in accelerating the heat
transfer to the core layer and extra adhesive is absorbed by the low moisture content
particles.
2.12.4 Surface Wet ability and Buffering
Surface wet ability and buffer capacity are two important characteristics of wood
/fibre materials because they influence the rate of adhesive penetration and curing between
the wood and adhesive. Pariadah et al. (2009) explained that good wetting on a wood/ fibre
material will cause the contact angle to become very small and as a result, the resin can
spread or flow spontaneously across the surface. The PH at glue line and buffering capacity
of the wood/ fibre significantly influence the curing time. Kenaf core and bast material
have greater sensitivity to acid compared to rubber wood.
46
2.12.5 Particle Size for board fabrication
A research conducted by Singha et al. (2009) showed that fibre size with 200
microns is more effective for particleboard fabrication compared to the short fibres (3mm)
and long fibres (6mm) due to larger surface area and more fibre/matrix interaction in the
particle reinforced composites. The chemical bonding (reaction between the methylol
groups of the resin with hydroxyl group of cellulose) depends on the urea formaldehyde
and natural fibrous materials. Yasin et al. (2010) reported that fine particles provide better
performance than coarse particles. During the board fabrication, fibre geometry plays an
important factor as it affects the whole properties of a particleboard. The length/diameter
ratio of fibres increases along with an increase in steam pressure and cooking time.
Ghalehno et al. (2011) further explained that fine particles in the face layers promote better
compact and adhesion.
Kasim et al. (2001) stated that small particle size influences the board by giving
better MOR and IB but resulted in higher water absorption (WA) and TS value. WA and
TS increased because the higher surface area provides more core particle movement, thus,
increasing the capacity to absorb water. Adding 1% of wax provides better WA and TS but
decreases the strength properties because of gluing resistance. Kim et al. (2009) explained
that the rough surface of kenaf fibre will result in better wet ability and mechanical bonding
because the OH bond from the fibres was eliminated and changed the polarization of kenaf
fibres from polar to non-polar. Good interaction between the matrix and the filler will
increase mechanical properties. Ghalehno et al. (2011) stated that an optimum particleboard
can be fabricated by using 40% fine particles and 60 % coarse particles with 9% resin in the
middle layer and 11% resin in surface layer with a pressing temperature of 1650C.
Ismail et al. (2011) stated that tensile strength decreased with the decreasing of filler
loading because the geometry of the kenaf core fillers, which is irregular shaped, are unable
to support stress transferred from the polymer matrix. The declining trend in tensile
strength could be explained by taking the de-wetting effect of the fibres. The interface
region of the fillers and the matrix act as a stress concentrator and gradually weaken the
interaction between the fillers and matrix, thus, leading to de-bonding at the interface.
47
Elongation at break will decrease with an increase in the fibre loading due to the increase of
stiffness and brittleness of the composite.
A research done on 30ųm and 300µm of rice husk flour showed that the smaller size
of rice husk provided better internal bonding (Lee et al. 2003). Xu et al. (2006) reported
that fine fibres have better bonding properties due to an increase in the bonding area. This
can be proofed when increasing the refining condition at low density board did not result in
higher IB because of higher bulk density of the fibres from severe refining condition, which
contributed to poor contact of fibres and consequently inferior inter-fibre bonding. Cheng et
al. (2006) further explained that coarse fibres will result in lower bulk density due to the
abundance of large fibres and fibre bundles that loosen the structures between fibres.
Kenaf core particles are short and thick, thus providing limited contact surface
between the particles. A study on the effects of particle size on tensile strength showed that
semi-circular end-shaped particles gave low strength, rectangular-shaped particle gave
superior strength, and those with flat, end-tapered and pointed, end-tapered shapes gave
moderate strength. The presence of short and thick core particles showed a low tendency to
resist the force and caused the joint to fail (Juliana, 2011). Tabarsa et al. (2011) stated that
rough surfaces will reduce the contact between the overlays and particleboards and created
a weak glue line and low bonding strength properties at the layers. The characteristics of a
particle surface are affected by the cutting tool geometry, crushing conditions and the
structure of the selected wood itself. Rough particles create a variety of voids in the
tracheas and fibres. To overcome this problem, scientists used high compaction and fine
screen particles to produce high quality surface for the particleboards. In addition, longer
pressing time was applied on the particles (some of the particles in vertical position may be
changed to horizontal position) and surface was densified; increasing the hardening process
of the adhesive and evaporating the moisture effectively. When fine particles (dust size)
and wood dust are used as the raw materials for a hybrid composite, the MOR and MOE
will decrease due to the low amount of woody cells and short fibres that failed to endure the
applied force during the test.
48
Based on an experiment, Zhongli et al. (2005) reported that 0.64 cm mesh particles
were covered better by the resin in the particleboard and had tighter bonds compared to the
1.26 cm mesh particles. This is because the adhesive failed to cover the surface area of 1.26
cm mesh particles. However, particles with the sieving size of 0.32 cm could be too large
and may result in the formation of weak bonding between the particles. The pores between
particles are visible and not all the particles were well bonded by the resin.
Haijun et al. (2003) mentioned that the fibre length of a material used the in
compounding process for a composite is critical because the wood flour-filled in PP
composite have the lowest mechanical strength this is because of the low aspect ratio,
which is far below the critical fibre length required for reinforcement. Flax and hemp have
shown to decrease in strength due to the bundles that are prone to being torn down to very
small size by the high-shear force. On the other hand, the dispersion of hydrophilic fibres
into the hydrophobic matrix to balance between dispersion and preservation of the fibres in
the polymer matrix must be attained to achieve high mechanical strength. Maya et al.
(2003) stated that short fibre reinforced rubber composites have become popular in the
industries because of the processing advantages and strength and stiffness properties,
modulus and damping. The aspect ratio of the fibres, fibre orientation and dispersion and
strong interface between fibres and rubber are found to increase the mechanical strength of
composites. Tajvidi et al. (2004) stated that fibres with high aspect ratio normally result in
better performance compared to particulate reinforcements.
Better mechanical strength like MOR and IB could be achieved by using smaller
size of particle (1mm) (Kasim et al. 2001). However, this will cause an increase in the WA
and TS due to the higher surface area of core particles, produced by the 1mm particle size,
which increased the capacity of the particles to absorb more water. A number of studies
have found that an increase in fibre length led to an increase in the impact strength. An
increase in the fibre length will also increase the pull-out energy. Therefore, fibre
dispersion becomes better and this leads to less fibre piled up and reduce the possibility of
fibre agglomeration in matrix. Consequently, every single fibre could interact with the
matrix more effectively (Wong. 2010). The findings of some experiments indicate that
49
longer fibre may cause poorer fibre dispersion due to the presence of sand particles that
made the interaction between the fibres and matrix became weak. Ability of sand particles
to abort energy is lower than the bigger particle size. The voids and trapped air in the board
caused internal defect in the composite. Nemli et al. (2003) reported that the small particles
size decreases the MOE and MOR values but improves the thickness swelling and internal
bonding of a composite. Dust and thin particles could fill the holes and increase the
connection between the particles and this will improve the thickness swelling and internal
bonding but at the same time, it will reduce the MOE and MOR strength. Based on a
research done by Teresa et al. (2011) on the effects of particle size on the properties of UF-
bonded giant reed particleboards, it was found that the IB strength increased when the
particle size was increased.
Another experiment done by Grigoriou et al. (2000) on the effects of particle size on
bending strength showed that kenaf fibre boards exhibited better bending strength
properties compared to industrial wood and kenaf core chips. The results of the experiment
also showed that the mechanical and hygroscopic properties of Kenaf fiber boards (UF
10%) made from the < 0.8mm fibre size were slightly affected compared to the bigger fibre
size ( 0.8mm- 5mm). The results of an experiment conducted by Cai et al. (2009) show that
larger size of panel results in greater internal steam pressure because the higher ratio of
volume to the edge area increased, and this resulted in more water being added to the panel
as well as less area for water to escape. In addition, the longer pathway from the middle to
the edges of the board created more resistance to the movement of steam and causing the
internal steam permeation from the centre to decrease and resulted in a high build up of
internal steam pressure. More steam was generated inside the mat when the press cycle
time increased and consequently, the internal steam pressure increased and this forced the
steam to escape through the voids between the particles and ultimately, from the edges of
the panel. The densified surface trapped most of the steam and this led to a high build up of
ISP. The screen with great number of small openings provided an alternate exit for the
steam under the mat during pressing and they allowed the steam to evaporate from the
bottom.
50
2.12.6 Hybrid Composite
Nowadays, the wood industry is practicing burning as a form of disposal of
unwanted wood. Research done by Campbell et al. (2007) showed that the composting of
composite wood products is becoming a bigger issue in Australia. By reprocessing of these
residuals, scientists came up with a new concept to convert waste into useful resources for
our real life applications. The main purpose of producing composite wood is to make these
products become more resilient to physical, chemical and biological stresses. Composite
wood products can be made by using wood fibres, flakes, chips or shavings together with
different glues, resin, water repellents and preservatives to produce sheet boards. The
shortage of rubber wood has become a serious issue in Malaysia. Recycled wood is slightly
inferior in comparison to the virgin wood but recycled wood has been adopted as the
preferred furnish due to the economic reasons (Suffian et al. 2010).
Fibreboards, particleboards and plywood are types of boards produced from
composite wood. Composite wood can be manufactured in a variety of ways and comprise
of different physical or chemical attributes that may affect the composting procedures and
end-product applications. These composite materials cannot be recycled due to the presence
of adhesives in them (Ghasemi et al. 2008). Studied on hybridization of two types of short
fibres at different lengths and diameters compared to fibres being used alone in single
polymer matrix. In contrast to fibres used alone in a single polymer matrix, hybrid
composites are materials made by combining two or more different types of fibres in a
common matrix and offer some advantages over each fibre. In hybridization, the focus is on
the enhancement of the mechanical properties by creating new types of hybrid composites.
The main purpose of creating a hybrid composite is to complement the weaknesses
in the selected fibres where the composites inherit superior and desired properties from the
selected fibres. The properties of the hybrid composite are mainly dependent on the fibre
content, length and orientation of individual fibre, extent of intermingling of fibres, fibres
to matrix bonding and the fibre arrangement. The mechanical properties of hybrid
composites were found to increase with the amount of waste fibres because they show good
51
reinforcement effects compared to the glass fibres. The success of hybrid composites is
determined by the chemical, mechanical and physical stability of the fibre /matrix system.
High structural performance can be achieved with non-exotic materials through
hybrid combinations assembled in optimized hybrid hierarchical configurations. Hybrid
composites will show the negative effects on tensile strength and Young’s modulus. On the
other hand, they show positive effects on the elongation at break, stiffness, strength and
moisture-absorption stability. The impact strength of the hybrid composites increase with
the addition of glass fibres because the fibres will interact with crack formation in the
matrix and act as a stress transferring medium. Hybrid composites with the kenaf exhibited
higher tensile and flexural module and strength compared to the wood flour (Jacob et al.
2009). The strength is increase when the rubber wood particles are incorporates in to kenaf
fibres (Jualiana et al. 2011).
According to Garcia et al. (2007), Young’s modulus is increased dramatically by
adding the amount of fibres. However, adding more fibres will reduce the tensile strength,
especially with the rice husks. This is because adding more fibres will increase the fragility
of composites. At higher fibre contents, the plastic does not embed the fibres properly and
this hinders the improvement in mechanical properties as the matrix content is not
sufficient enough to cover the fibre content to achieve higher mechanical strength. Higher
fibre content will prevent the matrix from wetting the fibres effectively. The flexural
strength increased when more kenaf was applied on the hybrid composite because the rice
husk with low aspect ratio acted as fillers rather than as fibres and this contributed to the
decrease in the mechanical properties. The impact strength increased when the fibre content
was increase up to 50%. Fibre size and types of the fibres also influence the impact
strength. Unnotched impact strength decreased after the addition of fibres due to the lower
aspect ratio and the fibres act as a weak link in the composites. As the fibre content
increased in the wood plastic composites, the unnotched impact strength of the composites
decreased.
52
Grigoriou et al. (2000) mentioned that the bulk density of the core chips and fibres
is lower than wood chips. When applied the wood chip up to 75% with kenaf core chips
will slightly affects the MOR and internal bond but reduced screw holding strength and
increased the water absorption and thickness swelling. Using the natural fibres in
combination with thermoplastic polymer had increased the mechanical strength but it also
has negatively affected the hygroscopicity of the final product. Kenaf core chips with the
low slenderness ratio showed insignificant effect on the MOR. By substituting the
industrial wood chips with kenaf core fibres up to 50%, the MOR is increased and the
roughness of the surface is reduced, but the soundness of the surface and screw holding
strength are negatively influenced the hygroscopic properties and spring back of the boards.
Hybrid composite boards showed greater spring back compared to industrial boards due to
their higher compressibility ratio.
Ozturk et al. (2010) mentioned that the maximum flexural strength of hybrid
composites; kenaf/fibrefrax with PF can be achieved by the ratio of 0.78:0.22. The flexural
strength of kenaf fibres is higher than fibrefrax in the original form. It is not surprising that
the flexural strength in a hybrid composite increases when higher ratio of kenaf fibres is
applied.
Hybrid composites are made by combining two or more different types of fibres in a
common matrix. Hybridization of two types of short fibres having different lengths and
diameters will offer some advantages over the single fibre in a single polymer matrix.
Kenaf fibres have higher aspect ratio and modulus in comparison with wood flour. Hence,
it is expected that when the amount of kenaf fibres is increased in the hybrid composites,
the MOE is improved. Kenaf fibres provide higher stiffness and strength values. In
addition, they have higher aspect ratios; making them suitable to be used as the fibrous
phase (Mirbagheri et al. 2007).
Behzad et al. (2011) mentioned that by decreasing the fibres content, the WA and
TS are decreased because more bonding sites were created, therefore, increasing the
dimensional stability of the boards. The WA and TS value could be reduced if some wax or
53
hydrophobic substances are added during the panel manufacturing process. The wax could
provide an excellent water resistance quality and better dimensional stability when the
board is soaked into the water. In hybrid composites, the water uptake was found to be less
than the unhybridized composites (Jacob et al. 2009). Low IB strength in hybrid composites
could be attributed to feckless adhesion in the specimens.
Bardak et al. (2011) stated that the density of a hybrid composite will be increased
because the structures are arranged in a more compact and tighter manner. High density
boards have more fibres and wood cells than the low density boards and this improved the
MOR and MOE values. Jawaid et al. (2011) explained that the void content of a good
composite should be less than 3%. The most common cause of voids is the incapability of
matrix to displace the air trapped within the woven or chopped fibres as it passes through
the matrix impregnation. Higher void content will lead to lower fatigue resistance, greater
susceptibility to water diffusion and an increase difference in mechanical properties. An
increase in compaction will cause the panel to be packed in a more compact and tightly
manner with reduced air trapped or pockets. Composites with lower void content showed
good adhesion between the fibres and matrix. Jawaid et al.(2011), stated that the impact
properties of composite materials are highly influenced by the constituent materials, fibre-
matrix interface, construction and geometry of the composites and the testing conditions. In
hybrid composites, the impact strength is lower than the pure composite because the pores
are filled up by the different types of fibres.
Mirbagheri et al.(2007) mentioned that the tensile strength increased regularly if the
kenaf fibres ratio is increased. The hybridization is improved the tensile strength properties
and the stiffness of a composite. Besides, adding longer fibres to wood flour plastic
composites improved the composite’s system. Naturally, kenaf fibres have higher modulus
than wood flour. Hence, it is expected that hybrid composites containing higher portion of
kenaf has better elastic modulus.
Nemli et al. (2007) stated that thickness swelling could be improved by increasing
the amount of resin and pressing time because the bonds between the particles is increased
54
and the resin will be cured effectively in the hot press. Internal bonding could be improved
by increasing the amount of resin and pressing time.
Tajvidi et al. (2004), stated that kenaf composites have the highest modulus
compared to waste fibre composites. Kenaf naturally has higher mechanical strength
compared to waste fibres and it is expected to have a higher reinforcing efficiency than
waste fibres. They found a combining 50% of kenaf with 50% waste fibres in a hybrid
composite. The composite had better tensile properties. The use of kenaf is improved the
stress transfer from the polymer matrix to fibres and more stress is borne by the stronger
kenaf.
2.12.7 Resin types
Phenol formaldehyde (PF) is another type of matrix that is applied in the composite
industry. Ochi et al. (2008) stated that by increasing the percentages of phenol
formaldehyde up to 400g the tensile strength will increase and then decrease as the PF
volume increases. The PF 400g will give optimum value for tensile test. The moisture
amount in composite increases with time and later becomes constant. The composite PF
500 will contribute to the maximum bending load of about 223.6N. Muehi et al. (1999)
stated the mechanical properties like Modulus of Rupture (MOR) , Bending Modulus of
Elasticity (MOE), Tensile properties and Internal bonding (IB) will increase by increasing
the phenol resin from 3% to 7% regardless whether the wax is present at the same time or
not. Applying additional wax will result in negative effects on the mechanical properties
and water absorption. Water absorption level can be decreased by increasing the phenol
resin from 3% to 7%.
Revista et al. (2009) explained that urea formaldehyde resin has low resistance to
humidity while the phenol-formaldehyde is recommended for external use or in high
humidity environments. Phenol and Urea do not have a significant effect on water
absorption and thickness swelling after 2 and 24 hours of immersion and can be explained
by the effect of interaction between the adhesive and the fibres by the physical-chemical
properties of each adhesive.
55
The adhesive content of 6% is presented higher percentages of water absorption.
However 9 and 12% contents are statistically equal and 3% is the economy in the
production process to reduce the production cost. By increasing the adhesive caused
increasing in the dimensional stability. PF has lower MOR and MOE value if compare to
UF. According to Dobbin et al.(1973) efficiency in glue-bond formation for phenolic
resins is approximately 10% higher than those product bonded with urea resin.
Anwar et al. (2011) stated that impregnating bamboo strips with low molecular
weight phenol formaldehyde has enhanced the overall strength properties of ply bamboo.
The resin acted as a kind of fixation agent in the cell wall and thus improving the stiffness.
By using low molecular weight, resin could easily penetrate into the wood cells and the
porous structure can be improved. Yang et al. (2007) explained that PF resin impregnated
the particleboards with higher MOR and MOE values compared to the urea adhesives.
After the distribution of PF resin on the surface and back of the particleboard, the structure
is more even and denser and this attributed to higher MOR and MOE values. The PF has
impregnated the particleboard with higher IB strength compared to the Urea adhesive due
to the even distribution of the PF on the chip. TS reading could be reduced by increasing
the PF concentration and higher compaction ratio had improved the efficiency of adhesive
bonding. An increase in density will lead to an increase in the TS value.
Lee et al. (2009) explained water absorption value increases with an increase in the
fibre content due to the hydrophilic nature and high porosity of the EFB fibres that
enhances the water diffusion process. An experiment conducted by Lee at al. (2009)
showed that water absorption takes a longer time to achieve saturation in PF boards with
higher fibre content. The presence of EFB fibres in the PF matrix has strengthened the
composite board. The impact strength decreased as the fibre content increased to 30%.
This is because higher fibre loading had caused poor dispersion of fibres in the matrix and
led to a weak stress transfer from matrix to fibres when the load is applied. The flexural
strength increased linearly with an increase of up to a maximum 20% in the fibre content
then dropped due to poor dispersion of EFB fibres in the PF matrix. The hardness and
56
stiffness of the PF board increased due to the strong interfacial bonding strength between
the fibres and matrix.
Ozturk et al. (2010) mentioned that stress-strain behaviour of any composite
depends on the strengths of the fibres and matrix, fibre volume fraction and the
effectiveness of bonding between the fibres and matrix. When a fibre-reinforced composite
is subjected to load, the fibres acted as a carrier of load and stress is transferred from matrix
along the fibres, leading to effective and uniform stress distribution and resulted in good
mechanical properties. The uniform distribution of stress depends on the population of
fibres. At low levels of fibre loading, the matrix is not reinforced by enough fibres and this
caused the bond between matrix and fibres to break because the fibres are incapable of
transferring the load to one another and as a result, stress is accumulated at certain points of
the composite and this led to low tensile strength. The lower flexural strength value of
kenaf fibre loading could attribute to poor enhancement of the matrix because of the lower
fibre content. The enbrittlement of a PF-kenaf fibre composite decreased with the addition
of kenaf fibres from 19-43 vol% and the high flexural strength of 43 vol% kenaf fibres
indicated good fibre-matrix adhesion and wet ability. The flexural strength decreased with
further addition of kenaf fibre loading from 43 to 62 vol% due to insufficient wetting of
matrix resin to fibres.
The impacts properties of a composite material are influenced by the interfacial
bond strength, the matrix and fibre properties (Ozturk et al. 2010). Impact will fail due to
fibre/matrix de-bonding, fibre and or matrix fracture and fibre pullout. A test conducted in
an experiment indicated that the load transferred by shear to fibres may exceed the
fibre/matrix interfacial bond strength resulted in de-bonding. On the other hand, if fibre
content is high, the volume of matrix resin is too small to deform plastically. 62 vol% of the
fibre loading on the PF composite will be the best for impact strength because of strong
bonding between the fibres and matrix.
Guru et al.(2009) stated that phenol formaldehyde can be mixed with urea
formaldehyde to decrease water absorption capacity and increase the thickness swelling of
57
particleboards because the hydrophobic properties that resulted from cross link binding in
resin, helped to improve the resin adhesion. Water absorption value increases by reducing
the phenol formaldehyde and can be used as a water resistant.
58
CHAPTER 3
Experimental programme
3.1 Introduction
This research aims to investigate and find the best resources available to substitute
the ones currently used in the production of particleboards. This chapter basically discusses
the raw materials and equipment used in the laboratory to fabricate the particleboards, the
manufacturing procedures, the procedures used in preparing the specimens, and the types of
tests carried out to determine the mechanical and physical properties of the specimens. The
particleboards were manufactured in a laboratory with the target density of 600kg/m3 by
using various mixture proportions with different parameters like fibre weight fraction,
density, matrix, size, waste wood, hybrid, bast and core fibre.
3.2 Outline of the experimental programme
Six (6) important factors affecting the mechanical and physical properties were
identified, namely; fibre weight fraction of the composite, size of the fibres/particles,
density, type of raw materials (such as kenaf core and bast fibres), type of matrix and
hybrid composites. The experimental programme was divided into three stages to
accomplish the objectives of this study.
In the first stage, the physical and mechanical properties of waste wood, kenaf core
and bast fibres were determined through a series of procedures. The physical properties
including fibre length and diameter after sieving, moisture content of the fibre, and
moisture absorption of the fibre were identified.
The second stage of the experimental programme was carried out to determine the
mechanical and physical properties of the particleboards. The particleboards were
fabricated by using the hot press machine.
In the third stage, mechanical tests (like tensile, bending, screw, internal bond, and
impact) were carried out to determine the mechanical and physical properties of the
59
composites. The optimum fibre weight fraction was determined and the methods of
fabricating the desired mechanical properties were used in structural application.
3.3 Materials
This section discusses the materials used in this research. The materials are
discussed briefly under the respective headings.
• Kenaf core fibres
The kenaf core fibres were obtained from Kenaf Natural Fibre Industries (KFI)
Kelantan, Malaysia. The separation process of the raw particle fibres was done by round
vibratory sieves (Unit Test) at different sizes of sieves namely (1 mm, 0.6mm). The
Particles were dried in an oven at 1050C for 2 hours to achieve moisture content of 5% or
less.
The round vibratory sieves were used to separate wanted/desired/needed elements
from unwanted materials. It is also used to jumble particles of different sizes as it has
different types of holes which are used to classify the size of fibres. The separation
efficiency for sieving is about 10 minutes for each operation. Figure 3.1 shows kenaf core
fibres of different sieving sizes after the separation process.
2mm sieving size 1mm sieving size 0.6mm sieving size 0.4mm sieving size
Figure 3.1 : Kenaf core fibres
• Kenaf bast fibres
The kenaf bast fibres were obtained from the same company as the core fibres.
Physical treatment of the bast fibres was done with 2% of detergent for 2 hours at the
60
temperature of 100°C, and they were then rinsed under the tap water until the detergent was
fully removed. The ratio of water and fibres for soaking should be 4:1. Next, the fibres
were dried under the sun and followed by an oven drying at 100oC for 24 hours. After the
drying process, all bast fibres were crushed into smaller size and stored in a dry place
before proceeding to the fabrication process. Before the fabrication process, the bast kenaf
fibres were dried in oven at 1050C for 2 hours to achieve moisture content of 5% or less.
Figure 3.2 : Kenaf bast fibres
• Waste wood
Figure 3.3 and 3.4 show the different sieving sizes of waste wood. The waste wood
was obtained from the Seven Seas Trading Company. It was dried under the sun, and then,
followed by an oven drying at 100oC for 24 hours. After the drying process, the waste
wood was stored in a dry place before proceeding to the fabrication process. Before the
fabrication process, the waste wood was dried in oven at 1050C for 2 hours to achieve
moisture content of 5% or less.
Figure 3.3 : 0.4mm sieving size of waste wood
61
Figure 3.4 : 1mm sieving size of waste wood
• Urea Formaldehyde
Urea formaldehyde (UF) resin 51.6% solid content, with specifications shown in the
Table 3.1, served as a wood binder and was obtained from Hexzachem Sarawak Sdn. Bhd.
The Urea-formaldehyde resin was used as a composite binder together with 1% of NH4CI
solution that acted as a hardener. Urea formaldehyde possesses strong positive aspects. It
has rapid cure rate and is basically cost-effective, non-flammable, and light in colour.
Table 3.1: Analysis of UF
Table UF resin Solid content 51.5% UF Appearance White & opaque Viscosity@300C 168CPS Specific Gravity@ 300C 1.198 PH@ 250C 8.0 Solid Content (3 hrs.@1050C) 51.5% Gel Time@1000C 41 S Free Formaldehyde 1.23% Water Tolerance@300C 197%
• Phenol Formaldehyde
Phenol formaldehyde resin with 41% solid content, with specifications shown in the
Table 3.2, served as a wood binder and was obtained from Bintulu Adhesive Company. PF
was used as an adhesive to bind the wood particles and is widely used in the plywood and
firewood industries.
62
Table 3.2 : Analysis Data for PF
PF resin Solid content 41% UF Appearance Dark red Viscosity@300C 90 pulse Specific Gravity@ 300C 1.191 PH@ 250C 13.26
• NH4CI
Ammonium chloride (NH4CI) was obtained from Hexzachem Sarawak Sdn. Bhd.
Table 3.3 shows the properties of NH4CI. It was used as a hardener and was applied with
the UF to accelerate the curing process. The main purpose of applying NH4CI was to hasten
the polymerisation process and change the UF polymer chain.
Table 3.3 : Properties of NH4CI
Properties Of Ammonium Chloride
Molecular Formula NH4CI
Appearance White solid hygroscopic
Odour odourless
Density 1.5274 g/cm3
3.4 Manufacturing Apparatus
Equipment of different sizes and functions were used in the manufacturing process.
This section explain the equipment used in the manufacturing process.
• Mixer & Spray
Figure 3.5 shows a normal mixer that had a cover and it was used to mix raw
materials. The cover was designed to have few small holes, each with a diameter of
3.0mm. The holes released pressure during the mixing process. The capacity of the
mixture was 0.2356m3 and the rotating speed was 800 rpm. The main purpose of
63
using the mixing drum was to make sure that the mixing was done evenly and to
avoid the spot occur on the particleboard.
Figure 3.5 : Mixing drum
A small 250ml container, as shown in Figure 3.6, filled with resin was kept beside
the drum and was connected to a spray gun. The spray gun was connected to a
compressor and was used to spray the resin mixture into the residue that was placed
inside the rotating mixer. The pressure gun had a 1.5mm nozzle for controlling the
resin flow. The main purpose of using the spray gun was to ensure that the resin
would fully bind the particles during the rotation. This uniformed mixing ensures that
the strength is distributed uniformly during the mechanical test in the later stage.
Constant pressure should be applied during the mixing process and the unnecessary
pressure will escape through the holes on the drum cover mentioned earlier.
Figure 3.6 : Container with spray gun
64
• Mould / Silicon glass map/ Steel plate/ Steel bar
A mould with the dimensions of 300.0mm X 300.0mm X 120.0mm, as shown in
Figure 3.7, was made of wood and used for casting particleboards before the hot press
process. Silicon glass map was used to release the particleboards after the hot press process.
It was also used to prevent the sticky problem after the heating process. The steel plate was
for transferring the raw material to the hot press machine. A 10.0mm steel bar was used to
set the thickness of the particleboard.
Figure 3.7 : Mould, Silicon glass map, Steel plate
• Hot Press
The Kobayashi hot pressing machine, as shown in the Figure 3.8, was used
to manufacture particleboards. The machine can only perform hot pressing and cold
pressing and it takes approximately 1 hr to reach 1800 C and take about ½ hr to cool
to room temperature (250 C). The maximum press area for the hot press is
500.0mm x 500.0mm. A high pressure hydraulic press was incorporated to develop
the hot pressing equipment for the project. The maximum pressing capacity of the
hot press machine is 150 tons. The maximum pressure needed for this project was
40 bars.
65
Figure 3.8 : Kobayashi Hot Press
• Cutting Machine
Panel saw SZIII, as shown in the Figure 3.9, was used in the cutting process.
Samples were prepared and cut from each test board according to the Japanese Industrial
Standard, JIS A 5908-1994. The sizes for the test pieces were marked on the cutting side of
the particleboards after the edges of the test particleboards were trimmed. After that, the
particleboards were sent to the chamber (as shown in the Figure 3.10) for the curing
process. Once the particleboards were prepared, they were left in the chamber at a
temperature of 250C and 65% humidity until the constant mass was achieved. This process
usually takes about 2 days to complete
Figure 3.9: Panel Saw SZIII Figure 3.10 : Chamber
66
3.5 Manufacturing Procedure
3.5.1 Process flow chart
Figure 3.11 : Process Chart
67
3.5.2 Calculation for the particleboard
1. Setting the dimensions or volume of Fibre board which is:
V = 30.0cm × 30.0cm ×1.0 cm = 900.0cm3
Percentage of resin or UFR solid content = 52.8% = 0.528
Density of fibre board = ρ = 600kg/m3 = 0.6g/cm3
2. Mass (fibres + UFR which is including moisture content) ,
m= ρV = 900 cm3×0.6 g/cm3 = 540.0 g
3. By setting 90% of mass is fibre weight and 10% of mass of UFR(including moisture
content):
Amount of fibres =540g × 0.9 = 486.0g
Amount of UFR (including moisture content) = 540g × 0.1 = 54.0g
Amount of UFR (without moisture content)
= 54 / 0.528
= 102.273g
4. Amount of NH4Cl hardener, measured by taking 1% of UFR (including moisture
content)
= 54 g × 0.01 = 0.54 g
5. By adding up all of the component’s amount,
= Fibres + UFR (without moisture content) + NH4Cl
= 486g + 102.273g + 0.54g = 588.813g
After adding up, put into the mixing machine for components mixing process. After
finishing the process, the mixing taken out and reweight again, it is observed that
68
total weight reduced By calculating percentage of mixing component’s weight loss,
Percentage of mixing components’ weight loss = × 100%
The percentage also indicate the weight loss created by mixing machine during
mixing process, therefore for other experiment or mixing process, 5 % will be added
for fibres, UFR and NH4Cl.
3.5.3 Particleboard Fabrication Process
The discussion under this heading explains the procedures adopted in making the
particleboards by using the kenaf particles (bast and core) and the waste wood as the raw
materials. Figure 3.11 shows the flowchart that highlights the major steps adopted in the
laboratory in making the particleboards. As mentioned earlier, the kenaf core particles with
different size was focus in this research follow by the waste wood and the kenaf bast fibre.
The core fibres with the sieving sizes of 0.4mm, 0.6mm, 1mm and >2mm were carried on
the research. However, only two different sizes for waste wood will carried on research;
they are the 0.6mm and 1mm sieving size. On the other hand, the kenaf bast with 1mm
sieving size will be focus on this project. Different types of raw material like bast, waste
wood, PF resin and hybrid to be investigate in this project.
The residues had very high moisture content when they were initially collected for
investigation. The residues were oven dried at a temperature of 1050C for 2 hours (as
shown in the Figure 3.12) to ensure that they were dried and the moisture had evaporated
completely.
69
Figure 3.12 : Dried the particles in the oven
The amount of UF resin, NH4CI, and raw materials were calculated by considering
the target density of the particleboard. Figure 3.13-3.16 shows the preparation process a
final board was put into the mixing drum. After the target density was decided, the weight
of the final board was calculated by multiplying the density with the volume of the final
board. In this research, parameters such as UF/PF resin, different sizes of particles,
different densities, waste wood, Kenaf core and bast fibres, different fibre weight fractions
and hybrid were investigated and analysed. The fibres were weighed in different fibre
weight fractions. The resin was also prepared based on the amount calculated for each fibre
weight fraction. Then, 1% of NH4CI that acted as a hardener was added into the UF to
accelerate the curing process.
Figure 3.13:Weighting raw
material
Figure 3. 14 : UF
preparation
Figure 3. 15 : NH4CI
preparation
70
Figure 3.16 : Resin is
reloaded
Figure 3.17 : Raw materials in
the drum
Figure 3.18 : Drum rotated at a
constant speed
After the preparation was done, the raw materials were put into the mixing drum.
The raw materials were mixed at a constant speed and the resin was sprayed on the surface
of the particles at the same time. The spraying continued until the resin finished.
The dried mixture was collected as shown in the Figure 3.19 and put into a pail for
weighing as shown in the Figure 3.20 and the weight loss was calculated. Next, the mixture
was transferred into a wood mould for the next process.
Figure 3.19 : The dried mixture was collected
Figure 3.20 : The dried mixture was weighed
The mixture was manually compressed in a wood mould as shown in the Figure
3.23 and the thickness of the mixture was constantly checked to ensure even mixing as
shown in the Figure 3.21. Two pieces of silicon glass map were used as a release agent for
the particleboard. The mixture was again compressed manually by using body weight as
71
shown in the Figure 3.23 to ensure that the particleboard would have a square shape when
removed from the wood mould.
Figure 3.21 : Level up the particles Figure 3.22 : Even mixing Figure 3.23 : Manually compress
The residues were transferred to the hot press machine for consolidation process.
Steel bars with the desired thickness were placed on both the particleboard sides. The
thickness of each stopper was 10.0 mm. To facilitate chemical reaction, reasonable pressing
times, temperature and pressure were applied on the particleboards. The temperature was
set at 180 0 C and the pressure was initially set to 40 tons for 2 minutes and then gradually
decreased to 20 and 10 tons where each pressure lasted for 2 minutes. The main purpose of
reducing the pressure was to avoid a build up of steam pressure within the board that could
potentially lead to a blow up if the steam was not released effectively.
Figure 3.24:Transferring the particleboard Figure 3.25 : Particleboard for hot press process
After the hot pressing process, the particleboard was cooled down at room
temperature and then sent for side trimming. Next, the particleboard was sent to the
chamber for a 2-day-curing process. The temperature of the chamber was set as 25 0 C with
a humidity of 65%. This is to avoid the particleboard from swelling and also to stabilise the
72
particleboard. After 2 days, the particleboard was cut into specimen pieces for the purpose
of mechanical and physical tests.
Figure 3.26 : Particleboard begging compress Figure 3.27 : Released heat
Figure 3.28 : Cutting process Figure 3.29 : Curing process
3.6 Specimens Preparation
The particleboard was cut into the specimen pieces for the specimen test. Each of
the tests has different dimension of the test pieces.
3.6.1 Test standards
Specimens for flexural test, screw withdrawal, internal bonding, tensile test, water
absorption and thickness swelling were prepared and tested according to the JIS A 5908 and
ASTM D 638 standards. All the specimens were prepared by following the guidelines as
shown in the Figure 3.29
73
Figure 3.30 :Cutting diagram of particleboard specimens for testing (mm)
• Flexural/Bending test:
Flexural/Bending strength is a mechanical parameter used in testing the behaviour
of a material and can also be defined as an ability of a material to resist deformation under
load applied perpendicular to its longitudinal axis. The size of specimens used in the test
was prepared based on the JIS A 5908 standard. The specimens were prepared with specific
dimensions; width of 50.0mm x length of 300.0mm x thickness of 10.0mm. The test was
carried out by using a three-point loading system applied on a supported beam. The
maximum load was measured by applying a load approximately 10mm/min at a mean
deformation speed from the surface of the test piece. The distance of two supports span (L)
74
was fixed at 150.0 mm and the load was applied at the middle points of two supports (L/2).
The flexural strength could be obtained by using the formula below:
223btPL
f =σ
Where σf (MOR) = stress in the outer specimen at midpoint, MPa
P (F) = load at a given point on the load deflection curve, N
L = support span, 150.0mm
b = width of beam tested, 50.0mm
t (d) = depth of beam tested, 10.0mm
MOE =SWx
btL
∆∆
3
3
4
MOE = Modulus of elasticity (MPa)
L = Span between centres of supports (mm)
ΔW= Increment in load (N)
ΔS=deflection with the load
t =thickness of specimen (mm)
b=width of specimen (mm)
Figure 3. 31: Flexural test with three-point loading
75
• Tensile Test
The main purpose of a tensile test is to investigate the ability of a material to
resist breaking under tensile stress and also to measure the properties of a material.
Part of the test is to investigate the reaction of the forces that begging applied in
tension. Tensile tests produce a stress-strain diagram that is used to determine the
tensile modulus, tensile strength and stress-strain profile of a material.
Figure 3.32 : Test apparatus of tensile test
The test was conducted under the standard laboratory atmosphere of 200C and with
65% relative humidity. The rate at which a sample was pulled apart in the test was 4
mm/minute. The specimens were prepared based on the dimensions in Figure 3.32 and
tested under the ASTM D 638 standard. The software used in this test calculated the tensile
strength, break force, yield force, yield strength and young modulus of the specimens.
Tensile strength = Force (load) / Cross section area
76
Tensile strength at yield = Maximum load recorded / Cross section area
Tensile strength at break = Load recorded at break / Cross section area
Figure 3.33 : Detail of tensile a test specimen’s dimensions (mm)
• Internal Bonding
The specimens were prepared based on the JIS A 5908 with the width of
50.0mm x length of 50.0mm x thickness of 10.0mm. The specimens were first
glued to the aluminium blocks on both surfaces by using hot melt glue and was
used to cold press for 24 hours. This procedure ensured that the glue would fully
stick on the aluminium blocks. A tension load was applied perpendicular on the
surface of each specimen at a uniformed rate of 2mm/min until failure occurred.
The maximum load of every specimen was recorded and then divided by the
sample’s cross section area. The main purpose of this test was to determine
the shear properties that would be applied perpendicular on the surface of a test
board and to measure the performance of an adhesive in wood composites.
77
F max= breaking load (N)
A = width (mm)
B=length (mm)
IB= Internal bonding (N/mm2)
Figure 3.34 : Test apparatus for internal bonding
• Screw Test
The specimens were prepared based on the JIS A 5908 standard with the
dimensions; width of 50.0mm x length of 50.0mm x thickness of 10.0mm. The centre of
each specimen was identified by using intersection method and a guide hole, about 3mm in
depth and 2mm in diameter, was drilled. Next, a 2.7 diameter screw was driven into the
pilot hole until the head of the screw is parallel to the surface of the specimen. The
specimen was then fitted into the holder and tensile force was applied to the screw at a rate
of 2mm/min and the maximum force in N was recorded by the system.
78
Figure 3.35 : Screw test Figure 3.36 : Screw test specimen
• Impact Test
The Charpy impact test is used to test the ability of an object to resist high-rate loading.
The test helps to determine the energy absorbed in fracturing a test piece at high velocity.
This absorbed energy is a measure of a given material's toughness. Specimens were
prepared based on the ASTM A370 standard with the width of 10.0mm x length of 55.0mm
x thickness of 10.0mm. There are two types of failure modes: brittle and ductile. Brittle
materials take little energy to start a crack, little more to propagate it to a shattering climax.
Ductile materials fail by being punctured in drop weight testing and require a high energy
load to initiate and propagate the crack. Many materials are capable of either ductile or
brittle failure; depending on the type of test, rate and temperature conditions.
Impact test Calculation:
Impact Test: Energy absorption (J) / Cross section ( m 2 )
3.6.2 Physical Test
• Water Absorption and Thickness Swelling
Water absorption test is used to determine the amount of water absorbed under
specified conditions. The main purpose the test is to check the behaviour of a composite
and the effects of the absorbed water on the dimensions of the affected composite. The test
specimens were prepared with the width of 50.0mm x length of 50.0mm x thickness of
10.0mm; with smooth and squarely trimmed edges. The specimens were conditioned to a
79
constant weight by drying them in an oven at 1000C for 24 hours. After the drying process,
the edges of each specimen were glued tightly to prevent water from being absorbed
through the sides of the surface when they were immersed in water. The specimens were
horizontally submerged about 3cm below the water surface for 2 and 24 hours. They were
then weighed after the excess water was drained off. The thickness was measured at the
same four points and the average was obtained. The following calculation can then be
made:
• Water absorption (%)
Wi = initial weight
Ww= wet weight
Water absorption (%) = Wi
WiWw − × 100%
• Thickness swelling (%)
Ti = initial thickness
Tw = wet thickness
Thickness swelling (%) = Ti
TiTw − × 100%
Figure 3.37 : Water absorption and Thickness Swelling test
80
3.7 Moisture for the Raw Materials
Natural fibres are hygroscopic material and this characteristic affects the overall
performance of the composites. If the fibres with the higher moisture content during the
fabrication, the bonding between the particles will be weaker due to the poor wetting
surface. Therefore, the moisture content should be kept to the lowest during the
fabrication process. Fibres with higher moisture content were removed by drying them in
an oven. The apparatus and material in this test included an oven and a balance weighing
machine refers to the Figure 3.38-40. About 10 grams of fibres were picked randomly.
Each specimen was weighed and the reading was recorded. The specimens were dried in
the oven at a temperature of 1050 C for 24 hours. After the heating process, the specimens
were weighed after they become stable and the reading of each specimen was recorded.
Figure 3.38 : Oven Figure 3.39 : Heating process Figure 3.40 : Weighing
3.8 Density Profile
The density of a particleboard is not uniformed along its direction of thickness. This
variation of density along the thickness direction of a particleboard is referred to as vertical
density profile (VDP) vertical density gradient. The VDP in a particleboard has a
significant influence on most of the mechanical properties like MOE, MOR, Screw test, IB
and tensile-strain. VDP formation is influenced by the rate of press closing, moisture
distribution in the mat and hot- press temperature, particle configuration, wood and resin
type. The VDP of a particleboard can provide information on the average raw density,
maximum raw density of top and bottom layer and actual position of sanding surface. The
81
measuring principle of raw density is based on a combination of x-ray transmission and
forward scatter. The imaging geometry will be show on the screen.
Figure 3.41: x-ray (VDP)
82
CHAPTER 4
Results & Discussion
4.1 Introduction
The overall results of experimental work presented in this chapter. These include
physical test of the natural fibres, physical and mechanical test of natural fibre reinforced
composite. In addition, this chapter described the parameters influencing the properties of
particleboards using the kenaf core fibres as residues. First, a single layer of a particleboard
was manufactured in the laboratory to find an optimal characteristic of the particleboard
before applying it as a hybrid particleboard. Second, six parameters were changed to
identify the best particleboard: weight fraction, particle size, raw materials (such as bast,
core and waste wood), matrix, density and hybrid composite. Finally, these processing
parameters and their upper and lower value were identified and incorporated into design of
the mix proportionate for hybrid particleboards. The results, analysis and outcomes for the
particleboards are discussed under the respective headings.
4.2 Fibre Properties
Natural fibre are discontinuous fibre, and fairly long as compared with the diameter.
The length and diameter of the natural fibre have great influence on the final product.
Before a composite to be created, the physical properties of the fibre should be study for the
better understanding and analysis.
4.2.1 Fibre Size
• Fibre Length
Figure 4.1-4.3 indicates the frequency of sieving fibres in different length range
.The data was taken from a random selection with 200 units of core fibres. The results show
that most of the core fibres are between the range of 851-1150µm for both 0.6mm and 1mm
sieving size. The higher frequency for bast fibres are between the range of 3-5 µm and
83
waste wood are between the range of 210-260µm for both the 1mm sieving size. The length
of the fibres has great influence on the stress distribution in the mechanical test.
The results of the analysis show that for the 1mm sieving size, 80% of the particles
were shorter than 1.9mm (length) and only 20% were >1.9mm. On the other hand, 80% of
the 0.6mm sieving size had 1.45mm (length) particles and 20% were longer than 1.45mm.
However, the bast fibres come with longer sizes and had to go through the crushing,
treatment and sieving process before the fabrication process with 47% less than 4mm in
length but 53% bigger than 4mm. The waste wood specimens were obtained from the
Seven Seas Trading Company in Kuching, Malaysia. The particles went through the drying
and sieving process; about 63% of waste wood were 2.6mm in length and 37% were bigger
than 2.6mm.
0255075
100125150175200225250275300325
550-850 851-1150 1151-1450 1451-1750 1751-2050 2051-2350 >2351
Freq
uenc
y
Length Range (Um)
0.6mm
1mm
Figure 4.1: Length of kenaf core fibre with 1mm and 0.6mm sieving size
84
0
10
20
30
40
50
60
70
1.00-2.0 2.01-3.0 3.01-4.0 4.01-5.0 5.01-6.0 >6.0
Freq
uenc
y
Length Range (mm)
Bast
Figure 4.2 : Length of kenaf bast fibre
0
10
20
30
40
50
60
70
80
108-158 159-209 210-260 261-311 312-362 363-504
Freq
uenc
y
Length Range (um)
Waste wood
Figure 4.3: Length of waste wood with 1mm sieving size
• Fibre Diameter
Figure 4.4 - 4.6 show the frequency of the diameter of kenaf core fibres in different
sieving size. A sample of 200 units of kenaf core fibres was taken at random and measured
using a digital microscope. The average diameter of the core fibres is approximately 551-
700µm for 1mm sieving size and 301-400µm for 0.6mm sieving size. On the other hand,
the diameter of the bast samples ranges between 71-98µm and waste wood between 39-
59µm.
85
0255075
100125150175200225250275
100-200 201-300 301-400 401-500 501-600 >601
Freq
uen
cy
Diameter Range (Um)
0.6mm
1mm
Figure 4.4: Diameter of kenaf core fibre 0.6mm and 1mm sieving size
0
10
20
30
40
50
60
70
80
90
42-70 71-98 99-127 128-155 156-183
Freq
uenc
y
Diameter Range (um)
Bast
Figure 4.5: Diameter of Bast
86
0
10
20
30
40
50
60
70
80
18-38 39-59 60-80 81-101 102-122 123-144
Freq
uenc
y
Diameter Range (um)
Waste wood
Figure 4.6 : Diameter of waste wood
(a) (b)
Figure 4.7: The Round Vibratory Sieves (Unit Test) and (b) The Sieves with Different Size of kenaf
Fibre (Osman et al. 2010)
4.2.2 Moisture Content
Moisture content is a critical parameter for developing vertical density profile and a
very significant parameter in particleboard production. High moisture content of natural
87
fibres reduces the bonding of fibres and matrix due to poor surface wetting. The moisture
content should be maintained at the lowest during the fabrication process. Poor surface
wetting for hydrophobic resin may cause interfacial shear bond and thus, lower the strength
of a composite. When excessive moisture is migrated to the particleboard core, it requires
additional pressing time to exit through the edges of the board to prevent de-lamination and
spring-back condition when the press is opening. Excessive moisture may cause rapid
densification of the surface and loosen the core. Hence, resulting in poor mechanical test
and may interfere with the polymerization of resin. Based on the results that shown in Table
4.1 of a moisture content test, it was found that waste wood fibres possess higher moisture
content than other natural fibres.
Table 4.1: Moisture content of the natural fibres
Natural Fibres Moisture content %
Kenaf core fibres with 0.6mm sieving size 5.3%
Kenaf core fibres with 1mm sieving size 9.1%
Kenaf bast fibres with 1mm sieving size 9.8%
Waste wood with 1mm sieving size 14.3 %
4.3 Density Profile of Particleboards
The density of a mat-formed hot-pressed particleboard is not uniform in the
thickness (vertical) direction, but varies through the thickness. The density profile of a
board was highly dependent on the particle configuration, moisture distribution, rate of
closing press, temperature of the hot press, reactivity of the resin and the compressive
strength of the component of the wood particles. Figure 4.8 shows that most of the
particleboards have higher density on the top and bottom regions compared to the core.
This is because the top and bottom regions were exposed to the hot-press and had better
heat for curing compared to core. When the press temperature controlled the rate of heat
88
conduction from the top and bottom platens to board surface, moisture plasticised the wood
particles and to the surface and less compression in the core layer, which improved the
compaction; producing higher layer densities at the top and bottom. A rapid press closing
speed generated higher initial pressure in the mat, consequently, allowing a shorter time of
heat and moisture transfer into the mat. The rapid pressing only allowed maximum
compression of wood closer to the surface and less compression in the core layer and this
resulted in higher surface density and lower core density. However, similar trend did not
occur in the bast fibre particleboards because the core absorbed the heat.
0
100
200
300
400
500
600
700
800
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9
Den
sity
Pro
file
(kg/
m3 )
Thickness (mm)
75% core & 1mm sieving size75% Bast & 1mm sieving size75% Waste wood & 1mm sieving size
Figure 4. 8: Density Profile Vs Thickness
The Figure 4.9 shows that 60% bast has a uniform density profile and was found to
possess homo-profile properties. 75% waste wood with 1mm sieving size was found to
have a U shape density profile. Wong et al. (1999) explained that homo-profile boards have
a significant influence on the mechanical test and correlated with the board mean density.
This can be due to a higher density closer to the surface that increases the flexural strength
and the reverse was true for the internal bonding strength due to lower density found in the
core. In addition, a particleboard made with higher moisture content on the surface and
lower moisture content could increase the density peak of the board with a slightly reduced
89
density at the core. Higher initial pressure with a short closing time during the hot pressing
process will result in higher face density with low core density (Nirdosha, 2007).
On the other hand, slow press closing produces an M shaped density profile.70%
waste wood possesses the M shape profile and is, therefore, categorised as a conventional
particleboard. A longer press closing speed helps to increase stress relaxation in a board
before final thickness is achieved. This affects the heat and moisture transfer as well as the
resin cure (Miyamoto, 2002). The longer press closing time causes the adhesive to
polymerize on the surface before sufficient inter-particle contact occurs inside the board.
Figure 4. 9: Density Profile Vs Thickness (U, M and Consistent Shape)
4.4 Mechanical Properties of Particleboards
Some parameters have a significant influence on the mechanical properties of a
particleboard. Below are the relationship between the parameter and the mechanical
properties. Measured data of bending strength, modulus of elasticity MOE, tensile strength,
young’s modulus, screw test, impact strength and internal bonding for all the experimental.
These data cannot use for direct comparison because each composite sample has a different
density. To eliminate the influence of the material density on mechanical properties, the
following equations are proposed to make the test parameters dimensionless.
90
dTE
(1)
dAJ
(2)
dVF
(3)
Where, E, d, T, J, A, F and V are modulus (MPa), composite density (N/m3), composite
thickness (m), impact strength (kJ/m2), force (N), area ( m2 ) and volume ( m3 ),
respectively.
4.4.1 Tensile Properties
• Tensile Stress vs Strain
Figure 4.10 indicates the stress-stain behaviour for various weight fractions of kenaf
core fiber reinforced urea formaldehyde composite at two different sizes; 0.6 mm and 1
mm. It can be seen that the load increased to the maximum value and then dropped sharply
as a brittle fracture. Some specimens experienced partial broken point or may be due to the
fiber pull-out. It was found that the core fiber was broken at the end. As illustrated in
Figure 4.10, the 0.6mm specimens with 75wt% showed the highest tensile strength which
was 12.44 MPa.The obtained results show that the decrease of fibers content increases the
strength of the composites due to the fact that there was insufficient resin to wet all the
fibers in the composite specimens. However, the same trend was not reflected in the 0.6mm
speciments with 85wt% because the fibers did not disperse uniformly in the composite,
thus preventing the matrix from flowing smoothly through the fibers.Besides, the fiber
strands are too coarse for the matrix resin to dissolve. Basically, the findings of the test
indicated that the performance of the composite materials depends not only on the fiber
and matrix properties but also on the quality of the interfacial bonding where constituents
interact chemically and mechanically. The presence of void could be another factor that
affects the tensile strength of the composite.
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Figure 4.10: Tensile stress vs strain at different weight fraction of kenaf core fibre using different size
• Effect of Density
Figure 4.11 shows that density has a significant influence on tensile strength.The
tensile strength of core fiber increased with increasing in the density.The optimal
dimensionless tensile strength for 600kg/m3 particleboard was 75wt% and 80wt% for
500kg/m 3 particleboard. A comparison between the 500kg/m3 and 600kg/m3, showed that
the latter has better tensile strength. This is because when density was increased, the
compatibility between the fiber and matrix was increased and led to an increase in the
strength of composite. When the density increased, it was found that the average pore size
decreased. The number of pores per unit area increased slightly and the pores became less
interconnected. However, lower density particleboards have high level of porosity. The
pores were exerted by stress-concentrating influence and consequently reduced the load
bearing.
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Besides, the higher compatibility caused the fiber to transfer the stress between the
matrix more effectively. Therefore, the particleboards had better stress concentraction and
managed to withstand the higher stress while being stretched or pulled before the failure.
The higher strength of kenaf core have served in imparting strength to kenaf
composite panel and part of it will be affected by fiber weight fraction. From the
experiment, tensile properties showed a significant decrease at the higher resin level for
both densities. The excessive matrix will decrease the tensile strength properties. Tensile
properties are affected by the compatibility of fiber with the urea formaldehyde, the
surface area of contact, particle size, shape and content as well as the intrinsic strength of
the UF phase ( Siew kim et al. 2009).
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Density 500kg/m^3
Density 600kg/m^3
Figure 4.11: Dimensionless tensile strength at different weight fraction of kenaf core fibre using
different densities
Figure 4.12 shows that dimensionless Young’s Modulus increased with increasing
fiber loading at the beginning and experienced drastic increase at 75wt% for 600kg/m3
(from 26.79 to 50.68) and 80wt% for 500kg/m3 (from 17.68 to 30.80). 600kg/ m3
particleboard with 75wt% fiber weight fraction showed the optimum dimensionless
Young’s modulus compared to all the particleboards. Young’s modulus of the 600kg/m3
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composite material had better mechanical properties than 500kg/m3composites
materials.Therefore, the specimens made of composite material with higher density were
slightly stiffer than the ones with lower density and could withstand higher stress at the
portion.
The fiber served as reinforcement because the major share of load was taken up by
crystalline fibrils that resulted in the extension of the helically wound fibrils along with the
matrix. An increase in the fiber weight fraction for both the particleboards showed a
decrease at the dimensionless Young’s modulus. This is because at higher fiber weight
fraction, the fiber acted as flaws and crazing occurred, thus, creating stress concentration
area that lowered the stiffness of the composites. Besides, the excessive fibers with small
amount of matrix created voids, and fibers are exposed more easily to enviromental
degradation. However, the addition of matrix for both the particleboards did not
significantly increase the modulus but slowly decreased for both the particleboards.
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Fiber Weight Fraction (wt%)
Density 500kg/m^3Density 600kg/m^3
Figure 4.12: Dimensionless young’s modulus at different weight fraction of kenaf core fibre using
different densities
• Effect of the Size
The results in the figure 4.13 show that 0.6mm sieving size had the highest
dimensionless tensile strength while the coarse fibres with <1.5-3mm sieving size had the
lowest dimensionless tensile strength. 0.6mm sieving size specimens had the highest
compatibility and enabled the stress to be transferred effectively between the fibres and
matrix. Therefore, the particleboards had better stress concentration and managed to
withstand higher stress when the specimens were stretched or pilled before the failure.
0.4mm sieving size specimens did not produce better result on tensile strength because the
smaller size particles reduced the stress concentration and prevented effective stress. The
coarse particles had a lot of voids between the particles, therefore, when the specimens
began to pull, they tend to fail easily.
95
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Dim
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Different Size Of Kenaf Core With 75% Weight Fraction
Figure 4. 13: Dimensionless tensile strength of kenaf core fibre at different sizes
The results in the Figure 4.14 show that the 0.6mm size specimens had the highest
dimensionless Young’s modulus. 0.6mm sieving size particles were fully bonded compared
to other the kenaf core fibre specimens; hence, the reason why the 0.6mm specimens had
higher dimensionless Young’s modulus. It was found that it was hard for the excess matrix
to flow through the particles of the smaller size specimens. This explains why the Young’s
modulus values of these specimens were not as high as specimens of bigger size. Besides,
the specimens of bigger particles required higher volume of matrix to substitute the spaces
between the particles.
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010203040506070
0.4mm 0.6mm 1mm < 1.5-3 m
Dim
en
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ss Y
ou
ng'
s
Mo
du
les
Figure 4. 14 : Dimensionless young’s modulus of kenaf core fibre at different sizes
• Effect of Weight Fraction at Different Types of Fiber and sizes
Figure 4.15 shows the maximum dimensionless tensile strength at different weight
fraction for different types of fibre. The results show that kenaf core fibres have better
tensile strength compared to bast fibres. The optimum dimensionless tensile strength
occurred at 0.6mm sieving size at 75wt% with the value of 0.275. It was also found that the
highest dimensionless tensile strength value for the core was at 1mm sieving size at 75%
weight fraction with the value of 0.208 while for the bast at 70% weight fraction with the
value of 0.149. It can be seen increased in dimensionless tensile strength for both sieving
size 1mm and 0.6mm up to 25% of matrix then decrease for the excessive matrix due to the
excess matrix will reduce the chains’ mobility, and consequently, produced a more rigid
and tough composite. The observation indicates that the incorporation of kenaf core filler
into the matrix improved the stiffness of the composites. The efficiency of a composite
depends on the fibre-matrix interface and the ability of the matrix to transfer stress to the
fibre. The dimensioless tensile strength decreased because of the inability of the fillers to
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support the stress tranferred from the polymer matrix. The reduction of the tensile strength
is partly attributed to the poor interfacial adhesion and low compatibility of kenaf core to
matrix when there was an increase in filler loading. The declining trend in tensile strength
could be explained by taking the de-wetting effect and the interface region of the filler and
matrix that act as a stress concentrator that weaken the interaction between filler and
matrix, thus, leading to debonding at the interface (Ismail et al. 2010). In bigger fibre size,
tensile strength is low due to the fact that the length may be not sufficient enough for
proper load distribution. Hence, failure can easily occur. It was observed that for the 1mm
fibre size, the percentage of fibre had a significant impact on the tensile strength.
Based on the results, waste wood at different fibre weight fractions had showed that
tensile strength increased dramatically when the fibre weight fraction decreased from
90wt% to 75wt% and proved that the fragility of the composites increased along with the
matrix. On the contrary, there were no changes in tensile strength for waste wood from
80% to 70% fibre weight fractions.
Waste wood consists of different sizes of particles even though the particles were
sieved by using a machine. When a waste wood particleboard is formed, the number of
flaws existing in the composite due to the different sizes of particles, bonded to each other
and the weak boundaries between the particles and the bubbles were increased and causing
the strength to decrease. Besides, inhomogeneous dispersion of matrix had caused the stress
field in the vicinity of aggregate to become high, which resulted in easier crack initiation
and propagation, and consequently led to a failure at low fracture level (Soundararajah,
2010).
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Figure 4. 15: Dimensionless tensile strength at different types of fibres
Figure 4.16 illustrates the dimensionless young’s modules of different fibre weight
fractions. The experiment shows that the dimensionless young modulus of particleboards
increased when the fibre weight is decreased. The results of the experiment showed that
core particleboard with 0.6mm sieving size, had the highest dimensionless young’s
modulus with the value of 61.33. At higher weight fraction of fiber, the fiber acted as flaws
which created stress concentration area; thus, lowering the stiffness of composite. Besides,
the matrix could hardly flow through every fiber because the additional fibers were a bit
excessive. Consequently, fibers could not be exposed more easily during the hot pressing
process. Based on the results, it was found that core particleboards with 0.6mm and 1mm of
90wt% of fibre weight fraction had similar properties because both have similar
dimensionless young’s modules value. The mechanical properties of Young’s modules are
influenced by the proportion of coarse fibers. Based on the results, the 1mm sieving size of
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fiber particleboard hads poorer mechanical properties than those with 0.6mm sieving size.
Smaller size of particles will create boards with better mechanical properties due to the
compaction of fibers into the spaces that created denser structures.
The Young’s modulus in 0.6mm sieving samples was relatively higher than that in
1mm sieving size because the fiber size in 0.6mm sieving was smaller. The smaller size of
fiber managed to achieve higher Young’s Modulus value and creadted more denser
structure for the particleboard.(Shibata et al. 2006). The toughness of the composites
increased when UF was added to the core fiber of different weight fractions ( 90% wt to
75% wt).
It can be observed that the stiffness and the Young’s modulus of waste wood
particleboards increased when the fiber weight fraction was decreased from 90wt% to
80wt% and decreased as the fiber weight fraction decreased to 75wt%. The presence of
polar group in the UF may contribute to electrostatic adsorption between the UF and waste
wood particles. This phenomenon is driven by the different charges acting on UF or waste
wood particles surface; this mechanism will strengthen the UF/waste wood particles
interface. It will hold them together and increase their resistance to deformity (Idris,2011).
Composite with higher level of fiber content was not be able to achieve higher Young’s
modules due to insufficient use of matrix as an adhesive in bonding the particles together.
Hence, the samples were easily to broken when pulled.
Particles geometry like shape and size have great influence on the strength properties.
Based on the observation, waste wood particleboards had lower Young’s modules if
compared to the kenaf core fiber and this could be attributed to the lower aspect ration of
waste wood particle. Besides, waste wood consists of a mixture of different species with
different percentages of chemical structure. Basically, because of the different percentages
of chemical structure, the waste wood specimens had lower young modulus even though
they were of higher densities compared to the kenaf fiber core specimens.
Bast particleboard achieved the optimum dimensionless Young’s modulus at 60% of
fibre weight fraction with the value of 57.254. The fact that bast particleboards have better
100
particle geometries may explain the reason why they possess much superior properties to
those of core particleboards. The longer and thinner particles will give better young’s
modules values than shorter and thicker strands. Kenaf core particles are short and thick,
resulting in limited contact surface between particles and thus lower the strength. Limited
contact surface will reduce the adhesive spread per area and affect the overall strength of
the particleboards. The different structure between bast and core fibres could be the
deciding factor that determines the overall strength of the particleboards.
The bast panels had higher density but lower value of Young’s modulus compared to
kenaf core panels due to the lack of pressure being applied during the compression of the
mat that created space between the particles. Besides, bast particles consists of elastic
properties that caused resistance during the fabrication process and resulted in the existence
of pores between the particles that were not well bonded by the resin. When the specimens
went through the test, the samples were easily to broken when they were pulled.
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Figure 4.16: Dimensionless young’s modulus at different types of fibres
• Effect of Matrix
Figure 4.17 shows the effect of UF and PF matrices on the tensile strength
properties of different types of raw materials. PF matrix shows better tensile strength on
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bast and waste wood specimens compared to the UF. On other hand, the even distribution
of UF matrix on the 1mm and 0.6mm particleboards explains why it had created better
results on tensile strength. The main reason for UF to have higher mechanical properties on
tensile strength is that the matrix bonded the particles well and there was better chemical
reaction between the matrix and kenaf core fibre. The kenaf core fibre managed to absorb
the UF matrix well on the wall cell and filled up the voids. On the other hand, the PF matrix
showed better cooperation between the bast fibre and the waste wood, this is because the
PF with the higher flow ability caused it easy to sick the particles in between and to fill up
the weak bonding area.
Figure 4. 17 : Dimensionless tensile strength at different resin
Figure 4.18 illustrates the effect of particle type and content on dimensionless young
modules. It can be observed that the stiffness and the Young’s modulus of waste wood
particleboards increased when the matrix was increased from 10wt% to 20wt% and
decreased as the matrix increased to 25wt%. The presence of polar group in the UF may
contribute to electrostatic adsorption between the UF and waste wood particles. This
phenomenon is driven by the different charges acting on UF or waste wood particles
surface; this mechanism will strengthen the UF/waste wood particles interface. It will hold
them together and increase their resistance to deformity (Idris,2011). Composite with
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higher level of fiber content was not be able to achieve higher Young’s modules due to
insufficient use of matrix as an adhesive in bonding the particles together. Hence, the
samples were easily to broken when pulled.
Figure 4. 18 : Dimensionless young’s modulus at different resin
• Effect of Hybrid
The results of the test outlined in Figure 4.19 are used to; determine the maximum
tensile strength of the composites, to identify the dynamic and static mechanical properties
of randomly oriented intimately mixed core and waste wood hybrid fiber reinforced
polyester composites. To begin with, it was found that the tensile strength of the
composites show a positive hybrid effect when the relative fiber weight fraction of the two
fibers was varied. The maximum tensile strength and the maximum stress transfer in the
1mm hybrid composite was 1:1 (core : waste wood) and for the 0.6mm was 3:1 (core :
waste wood). The mixture of core and waste wood (ratio of 1:1) for the 1mm sieving size
resulted in a significant improvement in the tensile strength of the composite because core
fibers have higher reinforcing efficiency than wood. The presence of core fibers had
improved the stress transfer from the polymer matrix to the fibres so that more stress was
borne by the stronger core fibers (Tajvidi, 2004). In addition, tensile strength also depends
103
on the fiber length and orientation to tranfer the stress. This test utilsed the unique
combination of core and waste wood to design hybrid bio-composites and from the results,
it was found that the incorporation of fibers resulted in increased tensile strength. Both of
the fibers were vital in increasing the interfacial adhesion and producing composites with
enhanced properties. The hybrid effect for the 0.6mm sieving size (75% core 25% waste
wood) is less stiff than the pure core particleboard but more stiff than the pure waste wood
particleboard.
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w.w 100%Dim
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1mm
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Figure 4.19 : Dimensionless tensile strength of hybrid fibres
Figure 4.20 shows the relationship between hybrid composites with the
dimensionless Young’s modulus. The results show that the hybrid composite with 1mm
sieving size (50% core, 50% waste wood) had similar properties as the 0.6mm sieving size
(75% core, 25% waste wood), and both of them also had the highest Young’s modulus
value. The hybrid composites did not show the positive effect on hybrid as compare to the
pure kenaf core and waste wood particleboard. The inconclusive of these results is possibly
due to the fact that core fiber or waste wood were bundles/ stick together and have varying
properties themselves which could account for inconsistencies even though in this study,
the amount of fibers used in the manufacturing of the composite was controlled in order for
each composite to have almost the same density (Ribot, 2011).
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100% w.w
Dim
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oung
's
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ulus
Types Of Hybrid
1mm
0.6mm
Figure 4.20: Dimensionless Young’s modulus of hybrid fibres
Figure 4.21 shows the specimens fitted on the tensile machine before undergoing
the tensile test. The experimental results show that the tensile specimen was broken at the
middle.
105
Figure 4. 21: Tensile test
4.4.2 Bending Properties
• Effect of Density
The effects of board density on the modulus of rupture (MOR) of kenaf core
particleboard were shown in the Figure 4.22. The MOR value increased significantly when
the board density increased from 500kg/m3 to 600kg/m3. The results shows that composite
with a density of 600kg/m3 needed the optimal fiber content of 75wt% fiber weight
fraction in order to obtain the highest dimensioless bending strength. However, composite
with a density of 500kg/m3 and with 80% fiber weight fraction showed the highest
dimensionless bending strength value . When density increases, the modulus of elasticity
increases proportionately. This is because as the material becomes denser, the molecules
have less room to displace with the same force, thus, leading to a higher stiffness (Paul et
al. 2006). The MOR results from samples with high density were proven to be able to
withstand the applied forces. The dimensionless bending strength value decreased with the
decrease of specific gravities in the composites because the porous structure decreased the
optimized fiber weight fraction (Shabata et al. 2006).
Dimensionless bending strength increases with the increase of density as shown in
Figure 4.23. This is because higher density composite is usually associated with higher
strength properties. The increase in strength properties could probably be associated with
higher compaction ration at higher density and was found to be stronger and stiffer with the
increase of density. The stiffen of the composite materials with 600kg/m3 density was
greater than the stiffness of the ones with 500kg/m3. The increase in dimensionless bending
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strength along with density is due to the fact that kenaf core is similar to other natural
organic fillers and can be categorized as high-modulus material. Higher density requires
higher stress in order for the equal deformation to take place, which resulted in the increase
of bending strength.
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Density 500kg/m^3Density 600 kg/m^3
Figure 4.22: Bar chart of dimensionless bending strength at different weight fraction of kenaf core
fiber using different densities
An experiment conducted on the effects of density on the MOE indicated that the
specimen containing 75% fiber weight fraction at density of 600kg/m3 has the highest value
of dimensioless MOR (39.66) while 500kg/m3 particleboards at 80% fiber weight fraction
will show the highest value of dimensioless MOR (30.11). The density of a board plays an
important role in increasing the MOE where all boards with higher density were observed
to be having greater MOE. This is expected because the inherent stiffiness of kenaf
particles might contribute positively to the overall stiffness of boards (Jani et al. 2010).
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Figure 4.23: Dimensionless MOE at different weight fraction of kenaf core fibres using different
densities
• Effect of the Size with 75% wt of Kenaf Core Ffibre
Figure 4.24 shows that the 0.6mm sieving size of kenaf fibres with 75% wt had the
highest dimensionless bending strength compared to the other specimens. This could be due
to the high compaction achieved by the 0.6mm particle size during the manufacturing
process. There was sufficient matrix to bond the particles and this reduced the voids;
resulting in better bending strength. 0.4mm sieving size had the lowest dimensionless
bending strength because the particles were too small and not able to transfer the stress
during the test. Coarse fibres with <1.5-3mm size also had low MOR values because of too
much voids between the particles that had reduced the strength.
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<1.5-3mm 1mm 0.6mm 0.4mmDim
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Different Size Of Kenaf Core Fiber With 75% Weight Fraction
Figure 4.24: Different size of kenaf core fibres with 75% weight fraction
The results in the Figure 4.25 show that the 0.4mm sieving size achieved the highest
dimensionless MOE compared to the other specimens. The smallest size of particles had the
highest compaction and resistance to bend when the material was stressed. Coarse fibres
tend to fail because low compaction created voids between the particles. In summary, the
results show that the compaction ratios as well as the length/thickness ratios of the same
wood species have a significant influence on the MOE.
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Figure 4. 25: Dimensionless MOE at different size of kenaf core fibres with 75 (wt%)
• Effect of Different Fibre at Different Weight Fraction and Sizes
Figure 4.26 shows the relationship between dimensionless bending strength and
fiber weight fraction for two fibers with the size of 0.6mm and 1 mm respectively. It is
clear that the board containing 75% kenaf fibres for both sizes has the highest value of
Modulus of rupture (MOR). The MOR of 75% weight fraction of kenaf fibres size of
0.6mm is 0.57 while the MOR for the 1mm is 0.42. It can be seen that the fibres with the
size of 0.6 mm has better results compared to the fibres with the size of 1 mm. This may be
due to larger surface and more fiber/matrix interaction in the particle reinforced composite.
Basically, the larger surface area of reinforced material will provide better interaction
between the polymer matrix and the core fiber. The chemical bonding accounts for
adhesion between urea formaldehyde and the natural fibrous material. The higher bond
strength obtained for UF matrix is due to the possible reaction between the methylol groups
of resin with hydroxyl group of cellulose (Singha et al. 2009).
The higher percentage of weight fraction did not show higher dimensionless
bending strength value because there was insufficient resin to wet all the fibers in the
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composite specimen. The MOR of samples with UF resins were increased significantly
from 90wt% to 75wt% but were insignificant when the loading of UF was greater than
70wt% for both the core kenaf. This shows that the presence of resins resulted in improved
bending strengths. With more resins available at higher resin content, more bonding sites
are made available, thus, improving the strength properties and increasing the dimensional
stability significantly; which can be attributed to the increase of the bond between the
particles and hardening of the resin efficiency during hot pressing (Ghalehno et al.2011).
At different weight fractions, the maximum MOR of a fiber, may be attributed to
the different diameters of the fiber and the compressive struture in the fiber cross section.
MOR was depend on the bonding strength among fibers, also depends on the individual
fiber strength and the fiber geometry (Jianying et al. 2006).
The results shows that at the beginning of 80% to 90% of fiber weight fractions, the
stiffness of the composite material filled with bigger size of particle 1mm is greater than
the stiffness of the ones filled with 0.6mm.However, the mechanical properties changed
from 75% to 70%; indicating that the smaller size of particle has greater bending strength
properties.
The MOR values of the bast and core particleboards show a similar trend. Bast
fibres have low bending strength value because of its spongy, elastic and soft properties.
During the fabrication process, when the board is manually compressed into the mould, the
bast fibres will spring back to their original form. Besides, the smoother surface and sticky
properties of the bast as compared to the core may interfere with the interaction between
the bast and the matrix and as a result the fibres become into contact each other.
Particleboards with 80%-90% fibres weight fraction were in homogeneous mixing on the
top and bottom surface and were improperly bounded with the matrix. As a result, it led to
poor interfacial bonding between the fibres and the matrix and hence resulted in a decrease
in the mechanical properties. With more resins available at higher resin content, more
bonding sites are made available, thus, improving the strength properties and increasing the
dimensional stability significantly; which can be attributed to the increase of the bond
111
between the particles and hardening of the resin efficiency during hot pressing (Ghalehno et
al. 2011). In addition, the mechanical properties of lignocelluloses fibres reinforced
polymer composites also depend on the extent of fibres-matrix bonding and the load
transfer from matrix to reinforcement. Higher magnitude of bonding will lead to better
mechanical properties.
During the waste wood particleboards fabrication, 80% of the fibres weight fraction
showed optimum MOR value. The overall result shows that the bending strength of MOR
for waste wood was lower than kenaf core fibres. Waste wood particleboard with 80%
fibres weight fraction was covered better by resin which helped to tighten the bonds
between the particles. In waste wood with 90 wt%, it was found due to insufficiency of
resin (to cover the particles); weak bonds were formed between the particles.
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Figure 4.26: Dimensionless of bending strength at different types of fibres with different fibres weight
fraction
Figure 4.27 shows the relationship between fibres weight fraction and MOE with
three different types of fibres (bast, waste wood and core). Fiber with the size of 0.6 mm
and at 70wt% weight fraction has the highest overall value of 56.163. An increase in the
fibres weight leads to improper interfacial adhesion between the fibres and matrix. Hence,
the strength of 90wt% fibres weight fraction is lower than those with higher resin content.
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Resin level has a significant influence on MOE. The experiment shows that insufficient
matrix will lessen the interfacial compatibility between the surface of the core kenaf fibers
and urea formaldehyde matrix. It is also found that the strength of core fibers contributed to
an enhanced strength of the natural fiber reinforced composites
Bast fibres with 70wt% of fibres weight fraction had the highest dimensionless
MOE value of 58.01. An increase in resin content resulted in higher MOE; irrespective of
density, and this proof that higher loading of resin will affect the MOE (Jani et al. 2010).
However, the value will drop after achieving the optimum fibres weight fraction due to the
excessive matrix applied during the bonding process. The bast specimens had lower MOE
values because the combination of different species of different chemical structures had
reduced the overall stiffness of the boards. The bast specimens may consist of particles with
elastic properties. During the fabrication process, the waste wood particles resisted the
compression process which created pores, thus making the specimens to fracture easily
when they were pulled. Particles configuration and orientation have great influence on
MOE.
The results show waste wood particleboards achieved the highest value of
dimensionless MOE at 80% wt and had showed similar trend where an increase in the resin
dosage had increased the MOE but the value decreased after reaching the optimum value.
The length of the flake has an significant influence on the MOE. Longer particle flakes will
result in higher MOE. Waste wood consists of a mixture of particles of different sizes and
species that may lead to poor bonding and caused the uneven of mixing occur.
113
0.00
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20.00
30.00
40.00
50.00
60.00
70.00
70% 75% 80% 85%
Dim
ensi
onle
ss M
OE
1mm Core0.6mm coreBastWaste woo
Figure 4.27 : Different types of fibres on MOE
• Effect of Matrix
Figure 4.28 illustrates the relationship between the dimensionless bending strength
of the different types of materials with two types of matrices; namely PF and UF. The
results show that the UF matrix had better bending strength value compared to the PF
matrix and this could be due to the fact that the former had good fibres- matrix adhesion
and wet ability. Adhesives have different chemistries and are bonded under different
condition of time, temperatures and pressure to variety of fibres/particles. It is, therefore,
not surprising to know that UF matrix had better bending strength value because UF matrix
has higher specific gravity than PF and could create higher value of bending strength.
UF matrix had developed a close contact with the substrates which led to stronger
and more durable bonds. UF showed the highest dimensionless bending strength on 0.6mm
kenaf core. This is because the matrix has bonded completely with the 0.6mm particles and
provided good reinforcement which provided better stress transfer from UF matrix to the
incorporated kenaf core fibres (Sultan, 2010). Besides, it had improved the compatibility by
changing one or both of the components which led to stronger and more durables bonds.
114
Specimens with PF matrix showed lower dimensionless bending strength which
could be attributed to the lower viscosity of PF that led to higher flow ability that caused
the matrix to flow through rather stick with the particles. UF matrix, on the other hand, had
lower flow rate that enabled it to hold the particles together and thus created better bonding
strength properties.
PF only showed better dimensionless bending strength on the waste wood and kenaf
core 500kg/m3 specimens. This is because the waste wood 500kg/m3 specimen had better
surface for the adhesive to interact with the substrate which created better mechanical
interlock between the matrix and the waste wood particles. Waste wood is a combination of
different types of species that created rough surface on each particle and when PF was
applied on the waste wood, the matrix penetrated easily into it and fills up the pores. UF
with low flow rate had caused the matrix hard to flow and remain some of the pores
without filling up the matrix. PF also showed better dimensionless bending strength on
500kg/m3 particleboard because the matrix bonded sufficiently with the particles and
created better compatibility. In a mechanical interlock, the adhesive provides strength by
reaching into the pores of the substrate. The mechanical interlocks provided more
resistance to shear forces.
115
0
0.1
0.2
0.3
0.4
0.5
0.6
Waste wood Bast Core 1mm density
600kg/m^3
Core 0.6mm density
600kg/m^3
Core 1mm density
500kg/m^3
Dim
ensi
onle
ss B
endi
ng
Stre
ngth
Difference Types Of Fiber Weight Fraction (75wt%)
UF
PF
Figure 4.28: Comparison between UF and PF
Figure 4.29 shows the effect of the two matrices on the MOE of panels. Boards with
the 0.6mm size/ UF exhibited the highest dimensionless MOE. It seems that UF resin acts
as a kind of fixation agent that penetrates into the cell wall of kenaf core fibres thus
improving its stiffness (Anwar, 2010). PF matrix with low molecular weight could easily
penetrate into the wood cell and fibres. The porous structure of the waste wood and bast
fibres can be penetrated easily by the resin and the resin either partially or fully bulk in the
parenchyma cell, hence, creating higher value of MOE (Anwar, 2010).
PF resin showed better results on MOE for the waste wood and bast specimens
because the matrix possess the better plasticity and flow ability. After the hot pressing
process, the distribution of PF resin on the surface and back of a particleboard could be
more even and denser and the values of MOE could be even higher (Yang, 2007).
UF and PF have different types of bonding energy. The results of a study show that
PF has higher energy than the UF and has the ability of activated flow, when the matrix
were droplets on the bast and waste wood, they will spread out spontaneously without any
external forces. The test showed that PF matrix had higher mobility on the wood surface
and bast. This high mobility caused the penetration to go through considerable depth into
116
compressed particles, which can result in their total impregnation. The penetration will
repair the weak zones that were usually damaged by cracks and fissures, by sticking them
together (Antonios, 2006). Technically, the reaction is characterized as an addition reaction,
which yields a cross-linked between the matrix and the particles.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
1mm core 0.6mm core Waste wood Bast
Dim
ensio
nles
s MO
E
Different Types of Fibers
UF
PF
Figure 4.29: Dimensionless MOE affected by the UF and PF
• Effect of Hybrid
The results in Figure 4.30 shows the effects of using hybrid composites (different
mixtures of kenaf core and waste wood) with 1mm and 0.6mm sieving sizes on the
mechanical properties in term of MOR. Based on the results, it was found that 1mm sieving
size (50%) kenaf core fibre with mixed well with 1mm sieving size (50%) waste wood and
showed the highest dimensionless bending strength. It was also found that by using lighter
particles (waste wood), the mechanical properties of the kenaf core composites improved
due to the higher compaction ratio where the voids were filled by smaller particles
(Tabarsa, 2011). Hybrid composite consisting of 25% kenaf core and 75% waste wood, for
both the 1mm and 0.6mm sieving sizes, showed similar mechanical properties on
117
dimensionless bending strength and had the lowest values compared to the other specimens.
The lack of strength in both specimens was caused by the low aspect ratio of waste wood
particles (Haijun, 2003). The slenderness ratio of kenaf core fibre and waste wood particle
has a significant influence on the mechanical properties because of the effect of particle
distribution. The transfer mechanism at which the applied stress is carried over from the
polymer matrix to the fibre reinforcement is completely dependent on the length and
orientation of the fibre (Terence, 2010).
By increasing the kenaf core fibres (1mm and 0.6mm) had increased the
dimensionless bending strength because of the tight structure had be formed and reduce the
adhesive linkage therefore the greater structural reliability had created. However, this did
not happen on 1mm sieving size for 75% core 25% waste wood particleboard because the
waste wood did not enough to fill up the pores which had created by the kenaf core fibre
with 1mm sieving size. It must be noted that if the fibre fraction for core fibre is too high,
the mechanical strength tend to decrease due to an increase in the occurrences of void
spaces within the vicinity of fibre-matrix interface (Terence, 2010).
The presence of kenaf core fibre had improved the waste wood properties. This
indicated that the kenaf core fibre had improved the stress transfer from the polymer matrix
to the fibres and more stress was borne by the stronger kenaf core fibres.
118
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0.10
0.20
0.30
0.40
0.50
0.60
0.70
25%Core 75%W.W 50%Core50%WW 75%Core 25%WW W.W 100%
g
g
Types Of Hybrid
1mm
0.6mm
Figure 4.30: Dimensionless bending strength on the hybrid particleboard with 1mm /0.6mm sieving size
for core with 1mm waste wood
Figure 4.31 shows the dimensionless MOE of different types of hybrid composites
for both the 1mm and 0.6mm sieving size. The test shows that the highest MOE for both
hybrid composites was with the ratio of 3:1 (core : waste wood). The results of the test
show that the MOE increased when there was an increase in the kenaf core fiber weight
fraction. It was found that when the core fiber (1mm sieving size) was increased, both the
density of the hybrid particleboard and the MOE value also increased (Garcia, 2011). An
increase in the density means that the particlebard is more compact and has tighter structure
(Bardak, 2011). Similar trend did not happen on the 0.6mm hybrid composite because the
improper bonding between the particles and matrix had created pores and reduced the
density. However, the 0.6mm hybrid composite still managed to achieve higher MOE value
compared to the 1mm hybrid composite. The main reason why the density of the 0.6mm
hybrid composite decreased but the MOE was still high was because the smaller particles
managed to flow into and fill in the pores, created by particles and matrix, and led to higher
MOE value during the test.
119
Based on the result, it can be said that pure core and pure waste wood itself have
lower MOE value compared to the hybrid composite. The hybrid effect were actualy
combine the mechanical properties of core and waste wood to creat better mechanical
properties. Combination of kenaf core fiber and waste wood creates composites with better
mechanical properties.
0
10
20
30
40
50
60
70
25% core 75% w.w 50% core 50% w.w 75% core 25% w.w w.w 100%
Dim
ensio
nles
s MO
E
Types Of Hybrid
1mm
0.6mm
Figure 4.31: Dimensionless MOE effected by hybrid 1mm/0.6mm sieving size with 1mm waste wood
Figure 4.32 shows the specimens fitted on the tensile machine before undergoing
the bending test. The result shows that the bending specimen was broken at the middle.
Figure 4.32: Bending specimen , bending process and the fail specimen after the test.
120
4.4.3 Internal Bonding
• Effect of Density
Figure 4.33 shows the relationship between the density and dimensionless internal
bonding. The results show that an increase in density will lead to an increase in the IB value
of kenaf core particleboard. 600kg/m3 particleboard with 75wt% showed the highest
dimensionless internal bonding with the value of 0.038.
This due to better adhesive binding between the binder and fibers, thus resulted in
greater ability to withstand the perpendicular forces (Jani et al. 2010). The results show that
high density resulted in higher compaction of the particleboard. The compaction of smaller
fibers into the spaces between the bigger fibers created denser structures. The denser
structures between the fibers provide a larger contact area between the fibers during hot-
pressing, which will create both a larger bonding area and lower porosity that resulted in
higher panel properties.
The particleboard with lower density did not result in higher IB and this could be
attributed to the high bulk density of the fiber from severe refining conditions, which
contributed to poor contact of fibers and consequently inferior interfiber bonding (Xu et al.
2006).
121
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
70% 75% 80% 85% 90%
Dim
ensio
nles
s Int
erna
l Bon
ding
Fiber Weight Fraction (wt%)
Density 500kg/m^3
Density 600 kg/m^3
Figure 4.33: Dimensionless internal bonding at different weight fraction of kenaf core fibres using
different densities
• Effect of the Size with 75wt%
The results in Figure 4.34 show that 1mm sieving size had the highest
dimensionless internal bonding while coarse fibres with <1.5-3 mm size had the lowest
dimensionless IB value. 1mm sieving size particles were increased the contact between
particles and matrix. As a result, the resin filled the gaps inside the core and increased the
tension resistance. The IB specimens will fail at the core particleboard because the core had
the lowest density at the middle and tend to fail easily.
122
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.4mm 0.6mm 1mm <1.5-3mm
Dim
ensio
nles
s Int
erna
l Bon
ding
Different Size Of Kenaf Core Fiber With 75% Weight Fraction
Figure 4.34: Dimensionless internal bonding at different sizes of kenaf core fibres
• Effect of Different Fibre at Different Weight Fraction and Sizes
The internal bond test results are displayed in Figure 4.35. It can be seen that the
composite board with 1mm fibres size has a higher internal bonding strength compared to
the 0.6mm fibres size. The bigger size of particle (1mm) was stronger than the smaller
particle 0.6mm. In general, composite board with 1mm fibres and 75wt% kenaf weight
fraction had the highest internal bonding strength with the value of 0.038. The resin
percentage was increased when the IB strength was increased due to better adhesive
binding between the binder and fibres; resulting in a greater ability to withstand the
perpendicular forces. The results of the test showed a trend that IB strength improved with
higher resin loading (Jani et al. 2010).
The reductions of the IB values for kenaf core particleboards may be attributed to
insufficient or over sufficient curing of the resin. It was found that different weight
fractions of core fibres with resin affected the glue line which either slowed down or
intensified the polymerization reaction rate. Thus, modification on the hot pressing time
123
and temperature were required to fully cure the resin so that compact particleboards could
be produced (Kamal et al. 2009).
From the experiment, it was observed that some of the cured resins were retained on the
fibres surface; indicating insufficient penetration of resin. There were some areas on the
core fibres surface without any trace of resin adhesive. The interaction effect between the
resin and core fibres was clearly seen in the experiment. The bonding strength between
polymer matrix and lignocelluloses depends on the surface topology of the particles
(Singha et al. 2009).
Particleboards with 80wt% bats fibres weight fraction have the highest internal bonding
strength with the value of 0.0077 and but does not show the highest mechanical properties
if compared to core fibres particleboards. The results show that there was an increase on
internal bonding up to a certain limit as the fibres weight fraction decreased but then, these
values decreased due to insufficient resin applied on both the bast and core. The results of
the test show a trend that IB strength is improved with higher resin loading (Jani et al.
2010; A. Grigoriou et al. 2000).
During the internal bonding test, most of the failure occurred at the low density core
region/midpoint of the thickness. This is because at the lowest density region, in a hot-
pressed panel and consolidation of the mat to obtain intimate particle, the particle contact is
at the minimum level. This can be seen on the density profile during the density profile test.
Unlike the bast, the results of the internal testing of the core indicate a dropping curve at the
middle point. Testing on the bast show a uniform pattern or increased in density at the
middle point of particleboard.
Bast particleboard showed low compaction condition compared to core particleboard.
Bast fibres possess the elastic properties and will maintain its original form during the
fabrication process. During the internal bonding test, the bast specimen failed by peeling
off condition at the middle of particleboard. Bast particleboard failed with peel off
condition due to inherent properties.
124
The particle size and shape of fibers affect the internal bonding process. The smooth
and fine surface of bast fibers led to rupture during the internal bonding test. Core fibers,
having finer particles compared to bast, showed higher internal bonding strength in the test.
Finer particles would lead to better bonding than stout particles due to wider contact surface
area. The adhesive content per unit particle surface area is higher for short particles than
for long ones at a given adhesive content. The internal bonding strength improves as the
core particle configuration changes from smaller size to bigger size. Coarse particle will
contribute better strength to particleboards.
Waste wood particleboards achieved the highest internal bonding at 80 wt%. Waste
wood specimens had showed weaker internal bond strength compared to core. This could
be attributed to the less porous surface of waste wood, which hindered the penetration of
adhesive resin inside the particles. Consequently, binding of the core layer, which is to a
considerable degree responsible for board strength, became weak. Different surface
structure of the waste wood used in the experiment had caused the waste wood specimens
to have low IB Strength. This explained the low value of IB strength, since at the resination
process, both waste wood and kenaf core fibres are mixed with the same amount of resin
but a smaller area of glue line is obtained in the former, which consequently reduced the
boards’ strength.
125
0.0000
0.0050
0.0100
0.0150
0.0200
0.0250
0.0300
0.0350
0.0400
70% 75% 80% 85% 90%
Dim
ensi
onle
ss In
tern
al B
ondi
ng
Fiber Weight Fraction (wt%)
Bast1mm Core0.6mm CoreWaste wood
Figure 4.35: Different types of fibres affected on internal bonding
• Effect of Matrix
Figure 4.36 illustrates the dimensionless of internal bonding of different types of
materials with 75wt% with two types of matrices. The results show that kenaf bast and core
specimens with UF matrix had better dimensionless internal bonding properties compared
to specimens with PF matrix that only showed better results on waste wood and 1mm core
with the density of 500kg/m3. PF, with higher flow rate and low solid content, required
higher temperature to cure the particleboard. PF required higher amount of heat in the
mattress to cure the core mattress because it is always at the lowest temperature compared
to the surface that was exposed to the hot plate.
PF has lower viscosity compared to UF, and thus, required longer and higher
hardening temperature (because it contains more liquid), and longer time to evaporate the
water into matrix. Wetting is an important issue; the kenaf fibres specimens did not show
better internal bonding strength results on the PF matrix because PF is water-borne. The
water mixed into the matrix created a weak chemical bond and caused a difficulty in
wetting the particles. PF showed better internal bonding properties on waste wood
specimens because waste wood has rough surface that caused the matrix to penetrate easily
126
into the surface and created better mechanical interlock. At the same time, the matrix will
fill up the voids and create better bonding between each particle.
0.0000.0050.0100.0150.0200.0250.0300.0350.040
Waste wood Bast Core 1mm density
600kg/m^3
Core 0.6mm density
600kg/m^3
Core 1mm density
500kg/m^3
Dim
ensi
onle
ss o
f int
erna
l bon
ding
Types of materials with 75%wt
UF
PF
Figure 4. 36: Dimensionless Internal bonding affected by resin
• Effect of Hybrid
Figure 4.37 shows the relationship between hybrid composite and internal bonding
strength. Hybrid composites with 25% core 75% waste wood (0.6mm sieving size) and
75% core 25% waste wood (1mm sieving size) showed the best internal bonding values
compared to the other specimens. The hybrid effect was not as good as a pure kenaf core
particleboard. This is because there was insufficient resin content to bond the particles and
to fill up the pores in the core and the waste wood mixture. Insufficient adhesion between
the hydrophobic polymers and hydrophilic fibers resulted in poor mechanical properties of
the composite. The weak internal bonding caused debonding of fibers ( core and waste
wood ) within the matrix that resulted in shear movement between the fiber and matrix
(Ribot, 2011).
The particle distribution size was different within the particleboard, both were
cented on the sieving size on 1mm and 0.6mm but the output particles still have different
127
in size. An increse in slenderness ratio produces a stiffer and stronger board in bending with
a decrease in internal bonding (Suffian, 2009). For the 1mm hybrid particleboard, an
increase in the weight fraction of core had improved the internal bonding strength because
the core fiber itself had better strength than waste wood. The 0.6mm hybrid particleboard,
however, did not show an improvement in the internal bonding strength. Due to its smaller
size compared to the 1mm hybrid particleboard, the 0.6mm hybrid particlebaord failed to
bear the shear force. Besides, the inhomogeneous mixing of the core fiber (0.6mm) with
waste wood had reduced the compaction of the particleboard.
Other than that, the rough surface area had reduced the contact between the matrix
and the particles (waste wood and core); resulting in a weak glue line and low bonding
strength properties of the core panel. The roughness of individual anatomical elements is
also created by variety void in trcheids and fiber. The surface characteristic of particles are
affected by the cutting tool geometry, crushing conditions during the cutting and
anatomical structure of wood (Nemli, 2006).
0.000
0.005
0.010
0.015
0.020
0.025
25% core 75% w.w 50% core 50% w.w 75% core 25% w.w w.w 100%
Dim
ensi
onle
ss I
nter
nal
Bon
din
g
Types Of Hybrid
1mm
0.6mm
Figure 4. 37: Dimensionless internal bonding affected by hybrid
128
Figure 4.38 shows the specimens fitted on the tensile machine before undergoing the
Internal bonding test. The result shows that the Internal bonding specimen was broken at
the middle
Figure 4.38: Internal Bonding Test and the specimen fail at the middle
4.4.4 Screw Test
• Effect of Density
Figure 4.39 shows dimensionless screw test of 500kg/m3and 600kg/m3
particleboards at different weight fractions. The result observed that in overall, 600kg/m3
particleboards with 70 wt% has the highest dimensionless screw test with the value of
3634.49. The results show that density has a significant impact on the performance of SW
in all boards ( Jani et al. 2010). Particleboards with 600kg/m3 density had better screw test
value compared to the particleboards with 500kg/m3 density because the former had good
stucture order. The higher compactibility caused the kenaf core fiber will to bind with the
matrix in a more effective way and increased the binding strength between the fiber and
matrix. Binding strength increased as compactibility increased; an event that enabled a
screw to be fixed securely on the particleboards and gave better screw withdraw reading.
In addition, screw withdrawal are affected by other factors such as screw geomatry, depth
of penetration into particleboards, particle grain direction, moisture content, raw material
and rate of loading during the test.
129
5001000150020002500300035004000
Dime
nsion
less S
crew
Test
Density Density
Figure 4.39: Dimensionless screw test at different weight fraction of kenaf core fibres using different
densities
• Effect of the Size with 75wt%
Figure 4.40 show that the 0.6mm sieving size had the highest dimensionless screw
test. The 0.6mm sieving size possessed good structure because the particles were
sufficiently bonded by the matrix. The effective binding had increased the compatibility
and enabled a screw to be fixed securely on the particleboards and resulted better screw
withdrawal reading. Coarse fibres were not bonded effectively during the fabrication and
this created voids that caused failure in the specimens during the test.
130
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1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
0.4mm 0.6mm 1mm <1.5-3mm
Dim
ensio
nles
s Scr
ew Te
st
Different Size Of Kenaf Core Fiber With 75% Weight Fraction
Figure 4.40: Dimensionless Screw Test at different size of kenaf core fibres
• Effect of Different Fibre at Different Weight Fraction and Ssizes
A Screw test was conducted to test the ability or strength of a board to hold the screw
on the surface or at the edge of the board and not to being pulled out by force. The Figure
4.41 shows the maximum withdrawal load of screw test of a composite board of 0.6mm and
1mm fibres sizes in five different weight fractions. The results show that 1mm fibres size
with 70wt% weight fraction could withstand the highest load of 3634.49 and had the
highest face surface screw withdrawal strength. It could be seen that the value of
withdrawal load for the 1mm kenaf fibres core increased as the weight fraction decreased.
Hence, the higher the resin content is, the higher the screw withdrawal load that it can
endure. This is due to the ability of the board to bear the pulling force after being resonated
with high resin dosage. The boards with high resin had caused the screw to be embedded
tightly and thus it resulted in better screw withdrawal strength.
In contrast, for 0.6mm kenaf fibres, the withdrawal load decreased when the weight
fraction increased. 0.6mm fibres size filled in composite with 75wt% weight fraction
showed the highest value compared to other weight fractions with the value of
3486.539.This explains the decrease in the withdrawal load value because it was difficult
for the matrix to flow through the fibres as the smaller fibres were compacted together. The
boards with more resins caused the screw to be embedded tightly and thus resulted in better
131
SW strength. When the weight fraction was decreased up to 75wt% for 0.6mm and 70wt%
for 1mm samples, the result was an increase in SW strength (Jani et al. 2010).
Bast fibres board with 70wt% weight fraction had the highest screw withdrawal value.
The results showed that the ability of the boards to bear the pulling force improved after
they were resonated with higher resin dosage. The results show that bast fibres and 1mm
core fibres with 70wt% and 75wt% fibres weight fractions shared similar mechanical
properties. The adhesive spread per unit area of particles could be effect the strength
(Jamaludin et al. 2001) of boards as shown in the test. With more resin available at higher
resin content, more bonding area is available, thus, improving the strength properties of the
boards. Higher resin content caused the screw to be embedded tightly and consequently,
resulted in better SW strength.
In comparison, the bast and core fibres are different in term of size; where former is
smaller in diameter. This may be the factor as to why the former has better results in SW
test. Ishak et al (2009) explained that the size of fibres affect the interfacial shear, normal
stresses and fracture characteristics. In addition, bast fibres have different chemical
composition like cellulose, hemicelluloses and lignin which are found to have strong
influence on the fibres’ mechanical properties. Kenaf bast fibres have higher cellulose
content as compared to kenaf core fibres (Du et al. 2008) and it has great influence on the
mechanical properties of the fibres themselves where it may provide strength and stability
to the plant cell walls and fibres (Ishak et al. 2009).
Bast fibres are more elastic if compared to core fibres and the fibres tend to bond with
each other, enabling the screw to be embedded tightly and thus making it difficult to be
extracted during the screw test. Higher compaction ratio may cause the board to have
higher strength.
Waste wood 80% with weight fraction achieved the highest dimensioless screw
strength. It was found that the withdrawal load for the waste wood specimens decrease
when the weight fraction increased. As the weight fraction decreased, the particles between
each other will be fully bonded caused the fastener holding capacity increased and the
132
screw was embedded tightly caused the ability of the thermoplastic to conform around the
thread of the screw allows continuous load transfer along the thread (Majid, 2008).
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
4500.00
70% 75% 80% 85% 90%
Dim
ensi
onle
ss S
crew
Tes
t
Fiber Weight Fraction (wt%)
Bast1mm core0.6mm coreWaste wood
Figure 4.41: Different types of fibres affected on screw test
• Effect of Matrix
Figure 4.42 illustrates the dimensionless screw test of different types of UF and PF
particleboards with 75%wt. The results show that PF matrix has the highest dimensionless
screw test for the waste wood. The matrix bonded fully with the waste wood par Screw
Testacies. The low viscosity of the PF allowed it to flow easily through the waste wood and
reduced the existence of voids. At the same time, the particleboards were filled with higher
dosage of resins as compare to other just which were flow over or evaporate during the
fabrication process. The higher resin dosage had caused the matrix to flow across surface,
transfer to other substrate and penetrate into the cell wall. When the screw was embedded
tightly into the particleboard, it was difficult to be extracted during the screw test.
The different chemical composition of the UF and PF basically explains why each
matrix interacts differently with the materials. The UF matrix interacted with the kenaf core
fibres specimens better than the PF matrix. Kenaf core fibres have hydroxyl groups in its
133
three main components like cellulose, hemicelluloses and lignin and the UF matrix can
react with hydroxyl groups better than the PF matrix. UF did not show better screw test
results because the waste wood is an absorber and will absorb water and lose some of its
strength when it is wet. Hence, the UF matrix had weaken hydrogen bonds to serve with the
waste wood and created the failure zone (Charles, 2005).
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
Waste wood 75%
Bast 75% 1mm Core 75% 0.6mm core 75%
Dim
ensio
nles
s Scr
ew T
est
Different Types of FIber with Weight Fraction 75wt%
UFPF
Figure 4.42: Dimensionless screw test affected by resin
• Effect of Hybrid
Figure 4.43 shows the relationship between the hybrid composites (core and waste
wood) and the screw test. The rsults of the test show that the hybrid effect did not provide
better results compared to the pure kenaf core and waste wood particleboards. It was found
that there was an increase in the screw strength of the hybrid composite with 1mm sieving
size with a 25% increased of kenaf core fibre. However, similar trend did not occur in the
composite with 0.6mm sieving size.
The main reason why hybrid composite with 1mm sieving size had better results
when the fiber weight fraction was increased was because the bigger size core fibre
cooperated with the waste wood and filled up the voids. The particle was in tight structure
134
order when the screw began to pull, causing it to be embedded tightly, and resulted in better
screw withdrawal strength.
Similar trend did not occur in the hybrid with 0.6mm sieving size because the small
particles were not able to substance the pulling force. The presence of bigger spaces
between the particles in the waste wood and 0.6mm kenaf core fiber mixture reduced the
screw withdrawal strength.
0
500
1000
1500
2000
2500
3000
3500
25% core 75% w.w 50% core 50%w.w 75% core 25%w.w w.w 100%
Dim
en
sio
nle
ss S
cre
w T
est
Types Of Hybrid
1mm0.6 mm
Figure 4.43 Dimensionless screw test affected at hybrid
Figure 4.44 shows the specimens fitted on the tensile machine before undergoing
the Screw test and the fail specimen.
Figure 4.44 : Screw Test and the fail specimen
135
4.4.5 Impact Strength
• Effect of Density
Figure 4.45, the optimal value to obtain the highest impact strength for fiber
composite with a density of 500kg/m3 was 80wt% and 600kg/m3 was 70wt% respectively.
From the observation, it was found that impact strength improved at different levels as the
weight fraction of fiber decreased. The improvement in impact strength could be due to
increment in matrix amount that allowed the applied stress to be transferred more
effectively due to increment in total fiber surface in contact with matrix. However, similar
trend did not occur in 500kg/m3 particleboard with 75wt% and 70wt%. This is due to
insufficiency of fiber to absorb the energy impact. Weak interfacial bonding of natural
fibers was mainly due to incompatibility between hydrophobic matrix and hydrophilic
fiber.
From the observation, some of the particleboards had a low impact toughness and
this could be due to ineffective energy dissipation mechanism at the interface. Irregular
hole size could be attributed to voids and air entrapment, which led to poor interface and
lowered the impact strength of the composite and created internal defect in the composite.
In addition, part of the low impact strength could also be attributed to poorer fiber
dispersion, which resulted in weaker interfacial bonding between the fiber and matrix that
consequently, created potential sites for crack growth.
136
0
20
40
60
80
100
120
140
70% 75% 80% 85% 90%Dim
ensi
onle
ss I
mpac
t T
est
( 10^3
)
Fiber Weight Fraction (wt%)
500kg/m^3
600kg/m^3
Figure 4.44:Dimensionless impact test at different weight fraction of kenaf core fibres at different
densities
• Effect of the Size with 75wt%
Figure 4.45, it was found that 0.4mm sieving size particleboard had the highest
dimensionless impact strength. The smallest size of particles has high compaction of
particleboard and managed to absorb the energy. The smaller particle size in the composite
was able to withstand fast impact load better than bigger particle size because the fibres
tend to slip from the matrix and left weak points or stress concentrated area. Particleboards
made from the coarse fibres tend to fail easily during the test because the loose structure
prevented them from absorbing the energy effectively. The bigger particle may not give
better impact strength as its size may cause poorer fibres dispersion as well as the presence
of sand particles in the fibres. Hence, the interaction between the fibres and matrix became
poorer as well. The introduction of bigger kenaf core fibres into the UF acted as flaw where
stresses were easily concentrated thus enabling a relatively low level of energy to initiate
cracks and causing the composites to fail. Different sizes of fibres could affect the
interfacial shear, normal stresses and fracture characteristic (Isaac et al. 2009).
137
0
20
40
60
80
100
120
<1.5-3mm 1mm 0.6mm 0.4mm
Dim
ensi
onle
ss Im
pact
Str
engt
h ( 1
0^3
)
Different Types Of Kenaf Core Fiber With 75(wt%) Weight Fraction
Figure 4.45: Dimensionless impact strength at different size of knead core fiber
• Effect of Different Fibre at Different Weight Fraction and sizes
Figure 4.46 shows the dimensionless impact strength behaviour of composite board
with 0.6mm and 1mm kenaf core fibers and at different weight fractions. The
dimensionless impact strength for 0.6mm fiber increased almost linearly until 80% weight
fraction with the decrease of the weight fraction of fiber. However, the exessive matrix of
had showed a decrese in the dimensioless impact test. This is because the low fiber content
and relatively smaller fiber size did not manage to dissipate the energy effectively. The
0.6mm fibres size is more compactly filled in composite and has created a large region for
stress concentration. The test on the 1mm kenaf core fiber showed that the specimen with
70wt% fiber weight fraction had the highest absorption ability compared to other weight
fractions.
.
138
The impact strength for both composites showed a decline beyond their optimal value.
This was due to higher fibres content. As a result, it led to poor interfacial bonding between
the fibres and matrix that caused a decrease in the mechanical properties. The maximum
fibres content that allowed the fibres to be fully moistened by the matrix for both
composites was subjected to the optimum fibres content and this explains why the
mechanical properties for both composites experienced a steep decline when both exceeded
their optimal weight fraction. Weak interfacial bonding of natural fibres may be due to the
incompatibility of hydrophobic matrices and hydrophilic of the fibres.
The results show that particleboards made from bast managed to withstand shock
loading better than core particleboards because of better bonding between the fibers and
matrix which created the least microvoids in the particleboards. Moreover, bast are more
compactly filled in composite and this provides large region for stress concentration. The
spacing between the fibers is more compact and this reduces microvoids. Waste wood
specimen had showed the highest impact strength at 70wt% when the fiber weight fraction
was reduced the specimen was improved.
The size and structure of the fiber will affect the interfacial shear, normal stresses and
fracture characteristics. Due to size factor, stout particles, like 1mm fiber, have poor fiber
contact between the fibers that prevent stress from being dissipated effectively. In addition,
there are more fiber ends in stout particles that created more stress concentration regions
which resulted in wider damaged zone area and less active fibers. Consequently, the impact
resistance ability deteriorates and this leads to a lower impact strength.
139
0
20
40
60
80
100
120
140
70% 75% 80% 85% 90%
Dim
ensio
nles
s Im
pact
Str
engt
h (1
0^3)
Fiber Weight Fraction (wt%)
1mm Core
0.6mm Core
Bast
Waste wood
Figure 4.46: Dimensionless impact strength at different type of fibres
• Effect of Matrix
Figure 4.47 show that PF produced better results on impact test compared to UF
when the former is mixed with different types of fibres. It can be seen that PF penetrated
well into the waste wood cell and the material had better resistance ability to withstand
fracture when undergoing stress at high speed. The impact properties of particleboards are
directly related to its overall toughness. The impact properties of fibres composites are
highly influenced by factors like, interracial bond strength, the matrix and fibres properties.
The results of the test show that PF matrix had better bonding properties as compared to UF
because its flow ability helps to substitute the voids and repair weak boundary and increase
the ability to absorb energy.
The impact failure is influenced by factors such as, fibres/matrix deboning, fibres
and matrix fracture and fibres pullout. During an impact test, deboning occurs if the load
(transferred by shear to fibres) exceeds the fibres/matrix interfacial bond strength. When
the stress level exceeds the fibres strength, fibres fracture will occur because the fibres tend
to pull out from the matrix and this involves energy dissipation (Ozturk, 2010). The
140
presence of fibres in UF matrix reduces the strength of the particleboards. This may be due
to the higher fibres loading where it caused difficulties in dispersion of fibres in the matrix,
consequently, leading to weak stress transfer from the matrix to the fibres when load is
applied (Chain, 2009).
020406080
100120140160180200
0.6mm 1mm Bast Waste wood
Dim
ensio
nles
s Im
pact
Tes
t (10
^3 )
Different types of fibers
UF
PF
Figure 4.47: Dimensionless impact strength at different resin Effect of Hybrid
• Effect of Hybrid Figure 4.48, hybrid effect had showed the positif effect on impact test. The
results of the test show that composites with 0.6mm ( 75% core 25% waste wood) had
the highest impact strength compared to the other composite specimens. The results of
the test also show that the impact strength of the hybrid composites was higher
compared to the pure kenaf core and waste wood. The impact properties of a hybrid
composite are directly related to its overall toughness that is highly influenced by the
nature of the constituent materials, fiber-matrix interface, construction and geometry of
the composites (Jawaid, 2011). Natural fibers like kenaf core and waste wood play an
important role in improving the impact resistance of fiber-reinforced composites as they
interact with the crack formation in the matrix and act as a stress transferring medium. (
Jawaid, 2011).
141
0
50000
100000
150000
200000
250000
25% core 75% w.w50% core 50% w.w75% core 25% w.w w.w 100%
Dim
ensio
nles
s Im
pact
Test
(10^
3)
Types Of Hybrid
1mm
0.6mm
Figure 4.48: Dimensionless impact strength at hybrid
Figure 4.49 shows the specimens fitted on the impact machine before
undergoing the impact test. The result shows that the impact specimen was broken at
the middle.
Figure 4.49: Impact test and the fail specimen
142
4.5 Physical Test on Particleboards
Some parameters have a significant influence on the physical properties of a
particleboard. Below are the relationship between the parameter and the physical
properties.
4.5.1 Thickness Swelling TS
• Effect of Density
Figure 4.50 shows the relationship between the thickness swelling and the fiber
weight fraction at different density. A decrease in the board density caused an increase in
TS because higher compressive set that exited in lower density boards, resulted in higher
swelling as stresses were relieved.The results indicated that water repellent chemicals could
be used to improve thickness swelling during the board production process.Lower thickness
swelling value indicates a more stable board.(Kamal et al. 2009)
Figure 4.50: Thickness swelling affected by density
143
• Effect of the Size with 75wt%
The result show that particles with the bigger size (<1.5-3 mm sieving size) have the
highest TS value at the first 2 hours and drop at 24 hours then return back as shown in
Figure 4.51. During the 24 hours soaking process, the TS value increased again because the
particles had expanded and some were released from the particleboards. It was also found
that 0.4mm size particleboard had the lowest TS value. This could be due to the low
diffusion rate in a particleboard with higher compaction that reduced the porosity. Higher
compaction had reduced water penetration into the particleboard; water needed longer time
to diffuse into the particles and as a result, the thickness swelling in the particleboard was
reduced.
0
2
4
6
8
10
12
0 hour 2 hours 24 hours 48 hours
Thic
knes
s Sw
ellin
g (%
)
Different Size Of Kenaf Core Fiber With 75% Weight Fraction
<1.5-3mm sieving size1mm sieving size0.6mm sieving size0.4mm sieving size
Figure 4.51: Thickness swelling affected by the different size of kenaf core fibres with 75wt%
• Effect of Different Fibre with different weight fraction and Sizes
Figures 4.52,4.53 shows the relationship between thickness swelling and fiber
weight fraction. The results indicated that the weight fraction of fiber was affected by
thickness swelling. A decrease in fiber weight fraction caused a decrease in the thickness
swelling. The wood was more repellent to water as more resins were incorporated into the
board (Jani et al. 2010). The high values obtained from the thickness swell tests were due to
the high percentage of highly absorpbent core fiber in the panels. The core fibers were very
144
short and constituted of a high percentage of total fiber content, thus, creating a very large
and highly absorbent surface area. Particleboards made from the 0.6mm core with 70wt%
fiber had the best performance among all the boards. Smaller size boards have lower
capacity in absorbing water due to limited surface area.
The thickness swelling of all the bast particleboards showed similar trend where an
increase in resin content will lead to a decrease in the thickness swelling. Specimens for
bast had show the higher thickness swelling value if compare to core because of bast
having the higher absorption ability if compare to core. Bast fibers had the lowest
performance due to low bonding strength caused by lack of fiber wetting (Juliana et al.
2011). Besides, bast particles are longer in size higher percentage of hemicelluloes than the
core and this attributed for more surface area to be exposed to the water,and therefore,
increased the moisture content.
The higher compaction ratio always absorb a lower amount of water than lower
compaction ratio because water entry into the higher density boards occurr at a slower rate
due to the decrease in porosity and increase wood material where they may repel water
from being absorbed into the boards. 0.6mm core 90wt% were not fullfill the theory this
may due to the lower moisture absorbed by boards .
Waste wood had similar trend where decreased the fibres weight fraction had
decrease in the thickness swelling as shown in Figure 4.53. This is because the matrix had
bonded the particles firmly and restricted the water to get into the particles. The decrease
thickness swelling in the particleboards occurred as the resin content increased could be
attributed to the chemical reactions, from cross-linking in hydroxyl groups found in the
kenaf core fibres, waste wood and resins, which led to lower water penetration (Jani, 2010).
It was found that particleboards made from the waste wood with fibres weight fraction
70wt% gave the best performance compared to the other boards. The thickness swelling of
particleboards increased as the resin decreased. This may be due to the high solubility
values of the particles.
145
When waste wood samples with 80wt% were immersed in water for 2-48 hours, the
samples had lower thickness swelling. This is because the samples had higher density and
the particles were arranged compactly with low porosity between the particles (Idris, 2011).
Figure 4.52: Thickness swelling affected by kenaf core fibres with different weight fraction and sizes
0
20
40
60
80
100
120
0 Hour 2 Hours 24 Hours 48 Hours
Thic
knes
s Sw
ellin
g (%
)
Soaking Times
Bast 70%Bast 75%Bast 80%Bast 85%Bast 90%w.w 70%w.w 75%w.w 80%w.w 85%w.w 90%
Figure 4.53: Thickness swelling affected by bast and waste wood with different weight fraction
146
• Effect of Matrix
Figure 4.54 shows the effects of UF and PF resin on thickness swelling. The results
clearly show that using PF will yield better thickness swelling results because it bonded the
particles surface fully.
Yang et al. (2007) explain that densification and resin efficiency are the two main
factors that will reduce thickness swelling capacity. PF resin has high flow ability that will
make it easy for the particles to bond together and fill up the spaces between the matrixes
which will result in higher compaction ration that improves the efficiency of adhesive
bonds which in turn would reduce the TS (Yang, 2007). Charles at al. (2005) explains that
UF adhesives have poor water resistance if compared to PF. Besides, the chemical structure
of PF has great influence on the thickness swelling.
Figure 4.54: Thickness swelling affected at different resin
• Effect of Hybrid
Figure 4.55 shows the thickness swelling (TS) of the 1mm and 0.6mm hybrid
composite specimens after they were immersed in water for 2, 24 and 48 hours. The results
show that both the 1mm and 0.6mm hybrid composite specimens with 25wt% core 75wt%
waste wood had the highest thickness swelling within the 2 hours. This is because the waste
147
wood itself has high water absorption ability when the hybrid composite was applied with
higher portion in the composite will cause an increase on the TS value (Behzad, 2011). The
poor absorption resistance of cellulosic materials, like waste wood and kenaf core fibres, is
mainly due to the presence of polar groups that attract water molecules through hydrogen
bonding. This leads to moisture build-up in the fibre cell walls and in the fibre-adhesive
interface (Tabarsa, 2010). In addition, an increase in the TS of the hybrid particleboards
could be caused by insufficient resins that are crucial in the bonding process. The fact that
kenaf core and waste wood are of different sizes also explain why there was space between
the particles. When the TS tests were conducted, it was found that water penetrated easily
into the wood cell and resulted in higher values.
0
5
10
15
20
25
0 hour 2 hours 24 hours 48 hours
Thic
knes
s S
wel
ling
(%)
Soaking Times
1mm core 100 %
0.6mm core 100%
1mm 25% core 75% w.w
0.6mm 25% core 75% w.w1mm 50% core 50% w.w
0.6mm 50% core 50% w.w1mm 75% core 25% w.w
0.6mm 75% core 25% w.w1mm w.w 100%
Figure 4.55: Thickness swelling of hybrid composites
Figure 4.56 shows the specimens on Thickness Swelling Test. It can be seen that the
thickness of the particleboard increased after soaking under the water for 2 to 48 hours.
148
Figure 4.56: Thickness swelling process and the output
4.5.2 Water Absorption
• Effect of Density
Figure 4.57 shows the water uptake of the composites for different fibres loading
after 2 hours of immersion time. The results show that water uptake increased with
immersion time and increasing of fibres loading. All the composites showed a similar
pattern of water uptake where sharp uptake occurred at the initial stage and then followed
by gradual increase until equilibrium was achieved. The water absorption value of the
composites was influence by the filler content. This may be due to the fact that an increase
of filler content in the composite resulted in the increase of free OH groups of
lignocelluloses fibres. Free OH groups came into contact with water through hydrogen
bonding, which resulted in water uptake and weight gain in the composites (Ismail et al.
2010).Water absorption can be reduced by limiting the fibres content, improving fibres-
matrix bonding, chemically modifying the fibres or simply protecting the composite from
moisture exposure. Denser particleboards, having lower void spaces in the structure, were
expected to absorb less water (Y. Copur et al. 2006). The temperature used by the hot press
machine during the fabrication had great influence on the particleboard. Low temperature
decreases the volatilization of moisture from particleboard and resin which creates different
water absorption rate for both medium.
149
The results of water absorption (WA) in Figure 4.57 show that there was a relatively
high absorption after 24 hours of soaking in water, with values ranging from 18.10%-
99.39%. Water absorption by composite materials depends on their porosity, amount of
cellulose fibres and their availability for incoming water. Water absorption increased
because kenaf core fibres was not bound with the UF matrix in the uniform way and
exposed into pores.
Figure 4.57: Water absorption affected by density
• Effect of the Size with 75wt%
Coarse fibres with <1.5-3 mm sieving size have greater water absorption value
compared to 0.4mm sieving size particleboard as shown in Figure 4.58. Smaller size
particles possess higher compaction ratio and this prevents water from flowing smoothly
into a particleboard. The water will flow into the particleboard at a slower rate due to the
decreased porosity. Bigger particles have high porosity and this enables water to flow
smoothly. In addition, larger area of the particles increases the water absorption ability.
150
0
20
40
60
80
100
120
0 hours 2 hours 24 hours 48 hours
Wat
er A
bsor
ptio
n %
Different Types Of Fiber Size With 75% Weight Fraction
0.4mm sieving size0.6mm sieving size1mm sieving size<1.5-3mm sieving size
Figure 4.58: Water absorption affected at different size of kenaf core fibres
• Effect of Different Fibre with different weight fraction and Ssizes
In general, all the particleboard had showed the similar trend when a decrease in the
weight fraction had decrease in the water absorption as shown in Figure 4.59
Particleboards produced by using 1mm sieving size will gave better results on water
absorption compared to 0.6mm sieving size. The higher water absorption was due to the
higher surface area of the core particles produced by using 0.6mm sieving size thus
increasing its capacity to absorb more water. The high values obtained from the water
absorption tests was due to the high percentage of highly absorbent core fiber in the panels.
The core fibers were very short and constituted of a high percentage of total fiber content,
thus, creating a very large and highly absorbent surface area. Water absorption values of
UF core particleboard increased with the fiber weight fraction due to the increase in the
hydrophilic property of natural fibers. During the test, some of the particles fell out from
the particleboard as a result of improper bonding between the fiber and matrix. Water
absorption decreased when resin content was increased. This may be due to chemical
reactions from cross-linking in hydroxyl groups found in kenaf and resin, thus, resulted in
lower in water penetration. Water absorption in all boards decreased as the kenaf particle
151
loading increased and this may be due to presence of excess resin in the board when its
density was increased (Jani et al. 2010). Higher level of UF dosing will slow down the rate
of water absorption because of UF repellent to the water.
0.6mm core with 90wt% and 1mm core with 80wt% showed decrease in water
absorption percentage because of lower moisture absorption within the boards. The
presence of good inter-particle bonding between the particle and matrix during the hot-
press process, which reduced the porosity of the boards, made the boards to become water
repellent. Bast have higher water absorption ability than core fibres and this may be due to
the fact that bast has wider surface that provides better exposure to the environment as
shown in Figure 4.60.
Waste wood particleboards had similar trend where an increase in the matrix led to
a decrease in the water absorption because the matrix had bonded the particles firmly and
restricted the water to get into the particles. It was found that particleboards made from the
waste wood and core with fibres weight fraction 70%wt gave the best performance
compared to the other boards. The water absorption of particleboards increased as the resin
decreased. This may be due to the high solubility values of the particles.
Waste wood particles have smaller size compare to the kenaf core fibres and this
explains why the waste wood specimens had lower water absorption. As the fibres size
reduces, the surface area also reduces and this affects the water absorption ability. As
higher surface area will increases the water absorption capacity. Waste wood samples with
80%wt were immersed in water for 2-48 hours, the samples had lower water absorption
value because the samples had higher density and the particles were arranged compactly
with low porosity between the particles.
152
Figure 4.59: Water absorption affected at kenaf core fibres
153
0
50
100
150
200
250
0 Hour 2 Hours 24 Hours 48 Hours
Wat
er a
bsor
ptio
n (%
)
Soaking Times
Bast 70%
Bast 75%
Bast 80%
Bast 85%
w.w70%
w.w75%
w.w80%
w.w85%
w.w90%
Bast 90%
Figure 4.60:Water absorption affected at waste wood and bast
• Effect of Matrix
Figure 4.61 shows the effects of UF and PF resin on water absorption. The results
clearly show that using PF will yield better water absorption results because it bonded the
particles surface fully. The effect of matrix on water absorption was depending on chemical
structure of the matrix. PF resin has high flow ability that will make it easy for the particles
to bond together and fill up the spaces between the matrixes which will result in higher
compaction ration that improves the efficiency of adhesive bonds which in turn would
reduce the WA (Yang, 2007). From the results, it was clear that the water absorption for
500kg/m3 particleboards and bast with UF increased from 2 hours to 24 hours then dropped
after 48 hours. UF has poor bonding ability because the particles can be released from the
particleboards due to the water absorption results had been dropped. Bast particleboard
with UF had highest water absorption results because it possesses higher water absorption
capacity and part of the reason was the matrix were improper bond the bast fibres. Part of
the reason why UF has higher results on water absorption is because it has higher viscosity
154
and higher solid content compared to PF which made it difficult for the matrix to flow
through and caused limitation on bonding.
Figure 4.61: Water absorption affected by kenaf core fibres and bast
• Effect of Hybrid
Figure 4.62 shows the water absorption (WA) of the 1mm and 0.6mm hybrid
composite specimens after they were immersed in water for 2, 24 and 48 hours. The results
show that both the 1mm and 0.6mm hybrid composite specimens with 25% core 75% waste
wood had the highest water absorption within the 2 hours. This is because the waste wood
itself has high water absorption ability when the hybrid composite was applied with higher
portion in the composite will cause an increase on the WA value (Behzad, 2011). The poor
absorption resistance of hem cellulosic materials, like waste wood and kenaf core fibres, is
mainly due to the presence of polar groups that attract water molecules through hydrogen
bonding. This leads to moisture build-up in the fibre cell walls and in the fibre-adhesive
interface (Tabarsa, 2010). In addition, an increase in the WA values of the hybrid
particleboards could be caused by insufficient resins that are crucial in the bonding process.
The fact that kenaf core and waste wood are of different sizes also explain why there was
155
space between the particles. When the WA tests were conducted, it was found that water
penetrated easily into the wood cell and resulted in higher values.
Figure 4.62: Water absorption affected by hybrid
Figure 4.63 shows the specimens on Water Absorption Test. The percentage of
water absorption was increased by the time from 2 to 48 hours.
Figure 4.63: Water absorption test
156
CHAPTER 5
Conclusions and recommendations
5.1 General
Currently, there are no extensive studies on the applications of natural fibre
reinforced polymer composites in the furniture industries. This study investigated the
physical properties of the pre-selected natural fibres; with the main objective of identifying
the most suitable natural fibres as a substitute to wood-based particleboards. Various
mechanical and physical engineering tests were conducted on the composite particleboards
and the results were compared with that of ordinary particleboards (based on the American
and Japanese standards).
5.2 Physical properties of natural fibres
Results of the tests show that waste wood particles has the highest moisture content
due to its hydrophilic nature as well as the combination of different types of species with
higher water absorption ability. Particles with high moisture content create high thickness
swelling and water absorption in the composite. The moisture content needs to be reduced
before the fabrication process is carried out to avoid moisture absorption and provide good
wetting for fibre surface.
5.3 Physical properties of the particleboard
• Density profile
The formation of vertical density profile (VDP) and its effect on the properties of
particleboards were reviewed in this study. The VDP of a particleboard is formed due to the
interaction between heat and mass transfer with resin during the production process.
Normally, a density profile shows higher density on the top and bottom compared to the
core. In addition, a VDP gives an indication of the effect of processing parameters on the
properties of a board. Therefore, measuring/observing a VDP helps to understand the
appropriate levels of hot-pressing and in optimizing the pressing process.
157
• Water absorption & thickness swelling
Board stability is dependent on properties such as thickness swelling or spring-back.
A particleboard will shrink and swell when subjected to environmental conditions; causing
desorption or adsorption of water. In this study, it was found that water absorption and
thickness swelling were affected by the density, size and type of particles, fibre weight
fraction, resin type and hybrid condition.
5.4 Mechanical properties of the particleboard
MOR, MOE and IB are the main strength properties of a general particleboard that
need to be achieved to meet the industrial standards. The MOE, MOR, IB, Screw Strength
and Impact of a particleboard are mainly dependent on the factors mentioned below.
Particle size has a significant influence on the mechanical properties of a
particleboard. 0.6mm is the optimum sieving size for a kenaf core particleboard on the
overall mechanical properties while 0.4mm sieving size only improves the impact strength.
Generally, increasing the density from 500kg/m3 to 600kg/m3 will improve the overall
mechanical properties of a particleboard. The results of tests were done in this research
show that reducing the weight fraction to a certain limit improves the mechanical strength
but then the strength decreases. Kenaf core fibres resulted in the best mechanical properties
in a particleboard compared to kenaf bast fibres.
The results of the tests also show that bast fibres had the lowest tensile strength,
young modulus, MOR and IB strength values but resulted in the highest impact strength
value on the particleboards. Waste wood particles showed the best mechanical properties
on the screw test but the lowest on MOE.
Waste wood particles can be improved by adding some portion of kenaf core fibres
as the hybrid composite for increasing the mechanical strength. By using the UF matrix on
a kenaf core particleboard, the matrix improves mechanical properties such as tensile
strength, young modulus, MOR, MOE, screw test, IB and impact strength. On the other
158
hand, PF matrix improves the overall mechanical properties of waste wood and kenaf bast
fibres.
5.5 Recommendations for future studies
• The advantages of using natural fibres should be understood by the
particleboard manufactures industries for reducing the timber demand.
Further manufacturing process of the particleboard should be conducted to
determine the ideal manufacturing process of the particleboard.
• Further researches should be conducted so that the fibres can be mixed even
with the matrix resin to obtain new highly efficient, economic and
manufacturer friendly composites.
• People should understand the advantages of the natural fibres and start to
cultivate in large scale in many regions throughout the world in order to
meet future demand for the sustainable development in industries sector.
• A study on performance of the natural fibres reinforced polymer composite
under various weather conditions is required. Degradation of the
performance of the material should be study.
• Other mechanical property test like bending strength under wet condition,
thermal insulation, scratch resistance and in-plane tensile strength test are
suggested to carry out in kenaf-UF reinforced composites.
• Different type of natural fibres in reinforcing polymeric composite is
required to find out the best performance of natural fibres reinforced
polymer for structural applications.
159
References
A.F.Halligan, A.P.Schniewind, 1974 ‘Prediction of particleboard mechanical properties at various moisture contents’ Wood science and technology, Vol. 8 ,pp.68-78
A.H.Juliana, M.T.Paridah, S.Rahim, I.Nor azowa, U.M.K.Anwar, 2012,’Properties of particleboard made from kenaf (Hibiscus Cannabinus L.) as function of particle geometry’, Materials and design Vol: 34, pp.406-411
A.N.Papadopoulos,E.A.Traboulay, C.A.S.Hill,2002 ‘One layer experimental particleboard from coconut chips-(Cocos nucifera L.)’ Holz als roh- und werkstoff, Vol: 60, pp:394-396, DOI 10.1007/s00107-002-0332-y
Amir Nourbakhsh,2008 ‘Mechanical and thickness swelling of particleboard composites made from three-year-old poplar clones’ Journal of reinforced plastics and composites 2010 29:481, DOI : 10.1177/0731684408097771
Angus Campbell.2007 ‘A literature review on the composting of composite wood products’ Recycled organic unit and Western Sydney Waste board, second edition
Antonious N. Papadopoulos,2006 ‘Property comparisons and Bonding efficiency of UF and PMDI bonded particleboards as affected by key process variables’ Bio Resources, Vol:1, No:2, pp:201-208 Anuar Hazleen, Sahrim Haji Ahmad and Rozaidi Rasid .2005 ‘ Impact and tensile properties of kenaf fiber reinforced thermoplastic natural rubber composites’, J. Solid St.Sci and Technol. Letters, vol 12, NO.1&2: 1-5
Anwar , U.M.K. Salim Hiziroglu, H. Hamdan, M. Abd.Latif, 2011 ‘ Effect of outdoor exposure on some properties of resin-treated plybamboo’ Industrial crops and products 33, pp:140-145
Arne Gulzow, Klaus Richter, Rene Steiger, 2011, “ Influence of wood moisture content on bending and shear stiffness of cross laminated timber panels” Eur. J. Wood Prod.Vol: 69,pp. 193-197, DOI 10.1007/s00107-010-416-z
Ayrilmis Nadir, Umit Buyuksari, Erkan Avci, Ali Nejdet Kuru, 2009 ‘ Utilization of waste tire rubber in manufacture of particleboard’
Bardak Selahattin, Bunyamin san, Gokay nemli, Huseyin kirci, Mehmet Baharoglu, 2011, ‘The effect of décor paper properties and adhesive type on some properties of particleboard’ International journal of adhesion & adhesives Vol:31, pp. 412-415
160
Behzad Bazyar, Ali Hassanpoor Tichi, Hossein Rangavar, 2011 ‘Particleboard made from fast growing aspen wood and old rail road ties’ Australian journal of basic and applied science, Vol:5, No:8, pp.548-553
Bharath .K.N. , R.P. Swamy 2009, ‘ Adhesive Tensile And Moisture Absorption Characteristics Of Natural Fibres Reinforced Urea Formaldehyde Composites’ International Journal of Recent Trends in Engineering, Vol. 1, No. 5. Bledzki AK & Gassan J.1999 ‘Composites reinforced with cellulose based fibres’. J Prog Bledzki,A.K, Sperber, V.E and Faruk, O.,2002 ‘Natural and wood fibre, Reinforcement in polymers’.Rapra Review Reports. Vol:13,No:152
Cai Zhiyoung, Michael birkeland, James m. wescott,Jane o’Dell, Jerrold e.winandy,2009,’Effect of press sizes on internal steam pressure during particleboard hot-pressing process’ Forest product journal
Camelia Cerbu, Ioan Curtu. 2009, ‘Flexural tests in case of some composites reinforced with carpinus/beech wood flour’ Annals of the University of Petroşani, Mechanical Engineering, 11 (2009), pp.29-36 Chai Lee-Lee, Sarani Zakaria, Chin-hua chia, Sharifah Nabihah, Rozaidi rosid, 2009 ‘ Physico-mechanical properties of PF composite board from EFB fibres using liquefaction technique’ Iranian Polymer Journal Vol:18,No:11, pp.917-923
Chai SP, Sumathi S, and Mohamed AR. 2008 ‘Utilization of oil
Charles J, Wegner, Theodore, Skog, Kenneth E, Ince, Peter J, Michler, 2005 ‘Critical literature review of relationships between processing parameters and physical properties of particleboard’
Chen.Y, O.chiparus, L.Sun, I.Negulescu, D.V. Parikh and T. A. Calamari. 2005 ‘Natural fiber for automotive nonwoven composites’ Journal of industrial textiles 2005 35:47. DOI: 10.1177/1528083705053392
Cheng xing, Bernard riedl, Alain cloutier, Stephen m,shaler, 2005 ‘Characterization of urea-formaldehyde resin petration into medium density fiberboard fibers’ Wood Sci Technol Vol:39, pp:374-384 DOI 10.1007/s00226-005-0294-4
Cheng Xing, Bernard Riedl, Alain Cloutier, Stephen M.Shaler, 2005 ‘Characterization of urea-formaldehyde resin penetration into medium density fiberboard fibers’ Wood Sci Technol Vol:39, pp: 374-384, DOI 10.1007/s00226-00-0294-4
161
Cheng Xing, S.Y.Zhang, James Deng, Bernard Riedl, Alain Cloutier, 2006 ‘Medium-density fiberboard performance as affected by wood fiber acidity, bulk density and size distribution’ Wood Sci Technol Vol:40, pp: 637-646, DOI: 10.1007/s00226-006-0076-7
Chew L.T., C.L.Ong,Suhaimi Muhammad. 1998 ‘ Urea-formaldehyde particleboard from yemane’, Journal of tropical forest science Vol:1,No:1,pp:26-34
Chung-yun Hse, Feng Fu, Hui Pan, 2008 ‘ Melamine-modified urea formaldehyde resin for bonding particleboards’ Forest product journal Vol.58, No.4 Chung-Yun Hse, Feng Fu, Hui Pan,2008 ‘Melamine-modified urea formaldehyde resin for bonding particleboards’ Forest Products Journal, Vol.58, No.4
Chunping Dai, Wayne wasylciw, Juwan jin, 2004 ‘Comparison of the pressing behavior of wood particleboard and strawboard’ Wood Sci Technol Vol:38, pp: 529-537 DOI 10.1007/s00226-004-0256-2 Clausen Carol A. Clause, S. Nami Kartal, and James Muehl. 2000 ‘Properties of particleboard made from recycled CCA-treated wood’,The international research group on wood preservation.IRG/WP-00-50146
Conner, A.H. 1996 ‘Urea formaldehyde adhesive resin’, Polymeric materials encyclopaedia, vol.II, CRC press, pp.8497-8581
Craig M. Clemons and Daniel F. Caulfield. 2005 ‘Natural fiber’. Functional Fillers for plastics. Wiley-VCH GbH & Co. KGaA, Weinheim. ISBN 3-527-31054-1
Dorota Dukarska, Janina Lecka, Rafal Czarnecki,2010 ‘Properties of boards manufactured from evening primrose straw particles depending on the amount and type of binding agent’
DU Y, Zhang J, Xue Y A , 2008, ‘Temperature-duration effects on tensile properties of kenaf bast iber bundles’ (Statistical table) Forest Product Journal
Garcia Miriam, Izaskun Garmendia, Javier Garcia, 2007 ‘Influence of natural fiber type in eco-composites’ Journal of applied polymer science, vol.107, pp:2994-3004
A. Grigoriuo, C. Passialis, E.Voulgaridis, 2000,”Experimental particleboards from kenaf plantations grown in Greece” Holz als roh-und werkstoff Vol: 58, pp:309-314
H Ismail, A hamid Abdullah and A Abu Bakar (2010) “ Kenaf core Reinforced High-density Polyethylene/Soya powder Composites: The Effects of Filler Loading and Compatibilizer ” Journal of reinforced plastics and composites. DOI: 10.1177/0731684409354392
162
Haijun Li, Mohini M.Sain,2003 ‘High stiffness natural fiber-reinforced hybrid polypropylene composites’, Polymer-plastics technology and engineering,Vol.42, No.5, pp.853-862
Hse Chung-Yun, Feng Fu, Hui Pan.2008 ‘Melamine-modified urea formaldehyde resin for bonding particleboards’ Forest products journal.Vol.58,No.4
Idris U.D., V.S.Aigbodion, C.U.Atuanya, Abdullahi.J, 2011, ‘Eco-friendly ( water melon peels): alternatives to wood-based particleboard composites’ Tribology in industry, Vol 33, No.4 Ishak M.R, Z.Leman,S.M.Sapuan, A.M.M Edeerozey, I.S.Othman, 2009 ‘Mechanical properties of kenaf bast and core fibre reinforced unsaturated polyester composites’ Materials science and engineering II(2010) 012006. DOI: 10.1088/1757-899X/11/1/012006
Ishak M.R., Z.Leman, S.M.Sapuan, A.M.M.Edeerozey and I.S.Othman ,2010 ‘Mechanical properties of kenaf bast and core fiber reinforced unsaturated polyester composites’, Material science and engineering 11: 012006
Ismaeil Ghasemi, Hamed Azizi and Navid Naeimian.2008 ‘Rheological behavior of polypropylene/kenaf fibre/ wood flour hybrid composite’, Iranian polymer journal Vol:17 No:3, pp:191-198
Ismawati P, 2006, Carboxymethylation of cellulose from kenaf (Hibiscus cannabinus l.) Core for hydrogel production master thesis university putra Malaysia.
Ivana Gavrilovic-Grmusa, Dr.Jovan Miljkovic, Dr.Milanka Diporovic-Momcilovic 2008 ‘Penetration of urea-formaldehyde adhesives in wood tissue ( part 1: radial penetration of UF adhesives into beech)Bulletin of the faculty of forestry 98, pp: 39-48.
Izrab Kamal, Abdul Rashid Abdul Malek,Mohd. Nor Mohd Yusof, Khairul Masseat, 2009 ‘Physical and Mechanical Properties of Flame Retardant-Treated Hibiscus Cannabinus Particleboard’ CCSE modern applied science, VOL. 3, NO.8
J.B.Zhong, J.Lv, C.wei, 2007, ‘Mechanical properties of sisal fibre reinforced urea-formaldehyde resin composites’, express polymer letter,Vol.1,No.10 ,pp: 681-687, DOI: 10.3144/expresspolymerlett.2007.93
Jacob Maya John, Rajesh D. Anandjiwala, Sabu Thomas, 2009 ‘Hybrid composite Chapter 12’, CSIR Materials Science and Manufacturing, Fibres and Textiles Competence Area
Jamal mirbagheri, Majid chaharmahali, Mehdi tajvidi, Saeed kazemi najafi, Yaser mirbagheri, 2010 ‘Mechanical and physical properties of wood-plastic composite panels’
163
Journal of reinforced plastics and composites, Vol.29.No.2/2010, DOI: 10.1177/0731684408093877
Jamal mirbagheri, Mehdi tajvidi, Ismaeil ghasemi, John c.hermanson,2007 ‘Prediction of the elastic modulus of wood flour/kenaf fibre/polypropylene hybrid composites’ Iranian polymer journal 16(4), pp.271-278
Jamal mirbagheri, Mehdi tajvidi, Ismaeil ghasemi, John c.hermanson,2007 ‘Tensile properties of wood flour/kenaf fibre/polypropylene hybrid composites’, Journal of applied polymer science, vol.105,pp.3054-3059
Jamaludn sim,Abd.Jalil hj.amad Jalaludin harun, Zaidon ashari abd.latif mohmod & Mohd nor mohd yusof.2001 ‘Properties of particleboard manufactured from commonly utilized malaysian bamboo’ Pertanika j. Trop .Agric.Sci.Vol:24, No:2, pp:151-157 ISSN: 1511-3701
James H. Muehi, Andrzej M. Krzysik, John A. Youngquist poo chow, Zhaozhen bao,1999 ‘Performance of hardboards made from kenaf’ Chapter 31, pp.367-379
James H. Muehl, Andrzej M. Krzysik, John A. Youngquist Jani S.Mohamad, M.P.Koh,M.Suffian,R.Rafeadah, U.Salmiah, K.Roszaini, J.Zaihan & M. Parid,(2010) Development of low density particleboard using kenaf care: mechanical and physical testing results, Forest research institute malaysia (FRIM)
Jawaid M, H.P.S. Abdul Khalil, A.Abu Bakar,2011, ‘ Hybrid composites of oil palm empty fruit bunches/woven jute fibre: chemical resistance, physical and impact properties’ Journal of composite materials , DOI: 10.1177/0021998311401102
Jianying Xu, Ragil Widyorini, Hidefumi Yamauchi.2006 ‘ Development of binderless fiberboard from kenaf core’. Journal wood science; DOU 10.1007/s10086-005-0770-3
Jianying xu,Ragil widyorini, Shuichi kawai .2005 ‘Properties of kenaf core binderless particleboard reinforced with kenaf bast fiber-woven sheets’, J wood sci 51,pp:415-420
Kaith, B.S, Chauhan, A 2008, ‘Synthesis, characterization and mechanical evaluation of the
phenol-formaldehyde composites’, E-journal of Chemistry, no. 0973-4945, 20 April 2008,
pp 1016-1019.
Kumar, M.G.C 2008, ‘A study of short areca fiber reinforced PF composites’, Proceedings
of the World Congress on Engineering 2008, World Congress on Engineering, vol. II,
London, United Kingdom.
164
Lee Sangyeob, Sheldon Q.shi, Leslie H.Groom, Yibin xue .2009 ‘Properties of Unidirectional Kenaf Fiber-Polyolefin laminates’,Wiley Inter Science
Lee, Y.K, Kim, S, Yang, H.S, Kim H.J 2003, “Mechanical properties of rice husk flour-
wood particleboard by urea formaldehyde resin’, Vol: 31,No.3, pp. 42-49
Li, Xianjun, Cai, Zhiyong, Winandy, Jerrold E, Basta, Altaf H.2010 ‘Selected properties of particleboard panels manufactured from rice straws of different geometries’ Bioresource Technology 101 (2010),pp: 4662-4666
M. Guru, Y.Aruntas, F.N.Tuzun, I.Bilici,2009, ‘Processing of urea-formaldehyde-based particleboard from hazelnut shell and improvement of its fire and water resistance’ Fire and materials; Vol:33. pp.413-419
M.Zampaloni, F.Pouroghrat,S.A. Yankovich, B.N.Rodgers, J.Moore,L.T.Drzal, A.K.Mohanty, M.Misra ,2006 ‘Kenaf natural fiber reinforced polypropylene composites: A discussion on manufacturing problems and solutions’, Part A: applied science and manufacturing Vol:38,pp.1569-1580
Majid Chaharmahali, Mehdi Tajvidi, Saeed Kazemi Najafi, 2008 ‘Mechanical properties of wood plastic composite panels made from waste fiberboard and particleboard’ Polymer Composites, DOI 10.1002/pc.20434
Majid Chaharmahali, Mehdi Tajvidi, Saeed Kazemi Najafi,2008 ‘Mechanical properties of wood plastic composite panels made from waste fiberboard and particleboard’ Polymer composites , DOI 10.1002/pc.20434
Maya Jacob, Sabu Thomas, K.T.varughese, ‘Mechanical properties of sisal/ oil palm hybrid fiber reinforced natural rubber composites’, composites science and technology , Vol:64, pp: 955-965 accepted on 2003
McNatt, J. Dobbin,1973, ‘Basic engineering properties of particleboard’ US Forest Service, Forest Products Laboratory Research Paper, FPL-RP-206
Miyamoto, K., Suzuki, S., Inagaki, T. and Iwata, R. 2002 ‘Effects of press closing time on the mat consolidation behaviour during hot pressing and linear expansion of particleboard’, Journal of Wood Science, vol. 48, pp.309 - 314 Mohammad dahmardeh ghalehno, Morteza nazerian,2011 ‘Producing roselle (Hibiscus sabdariffa) particleboard composites’ Ozean journal of applied sciences Vol:4, No:1, ISSN 1943-2429
165
Muehi, J.H, Krzysik, A.M, Youngquist, J.A, Chow, P,Bao, Z 2003, ‘Performance of hardboards made from kenaf’, Library of congress cataloging-in-publication data, pp 344-377
Munirah moktar, Abdul razak rahmat and Azman Hassan .2007 ‘Characterization and treatments of pineapple leaf fiber thermoplastic composite for construction application’ Research thesis. Universiti Teknologi Malaysia.
Nemli Gokay, 2003 ‘ Effects of some manufacturing factors on the properties of particleboard manufactured from alder (Alnus glutinosa subsp. Barbata)’ Turk J Agric For Vol: 27, pp: 99-104
Nemli Gokay, Ismail Aydin, Emir Zekovic,2007 ‘Evaluation of some of the properties of particleboard as function of manufacturing parameters’ Materials and design Vol:28, pp: 1169-1176
Nirdosha, G. and Setunge, S. 2007 ‘Formulation and process modelling of particleboard Ozturk Sultan, 2010 ‘ Effect of fiber loading on the mechanical properties of kenaf and fiberfrax fiber-reinforced phenol-formaldehyde composites’ Journal of composite materials. Vol.0. No.00/2010 DOI: 10.1177/0021998310364265
Padil, M., Tom, P, Yaakob, M.Y, 2008 ‘Kenaf fiber plate’, Faculty of manufacturing engineering, University industry centre.
Paridah M.T ,P.S.H’ng, B.N.Khor, N.Tadashi, A.S.N.Aini ,2009 ‘Anatomical structures and fiber morphology of new kenaf varieties’, Asian Journal of Scientific Research Vol: 2,No.3, pp : 161-166
Paridah MT, AW Nor Hafizah, A Zaidon, I Azmi, MY Mohd Nor Yuziah.(2009) Bonding properties and performance of multi-layered kenaf board. Journal of Tropical Forest Science Vol:21, No:2,pp:113-122
Paul W, Ohlmeyer M, Leithoff H, Boonstra MJ, Pizzi A. 2006 ‘Optimising the properties of OSB by a one-step heat pre-treatment process’ Holz- RohWerkst, Vol:64, No.3,pp:227-234 Polym Sci,vol. 24,pp. 221–74
Poo Chow, and Zhaozhen Bao ‘Performance of hardboards made from kenaf’ production using hardwood saw mill wastes using experimental design’. Composite Q.Y.Soundararajah, B.S.B.Karunaratne,R.M.G.Rajapakse,2010 ‘Mechanical properties of poly(vinyl alcohol)Montmorillonite Nanocomposites’ Journal of composite materials 2010 44:303, DOI: 10.1177/0021998309347040
166
Rafael Farinassi Mendes, Lourival Marin Mendes, Jose Benedito Guimaraes Junior, Rosimeire Caval Cavalcante Dos Santos, Lina Bufalino.2009 ‘The adhesive effect on the properties of particleboards made from sugar cane bagasse generated in the distiller’
Ribot, N.M.H, Ahmad, Z.,Mustaffa, N.K,2011 ‘Mechanical properties of kenaf fiber composite using co-cured in-line fiber joint’ International Journal of Engineering Science and Technology Vol.3, No.4, ISSN: 0975-5462
Roy D.Seale, Terry sellers, Jr. Marty J. Fuller.1996 ‘Kenaf core board material’ United States Patent
Saira taj, Munawar ali munawar and Shafiullah khan 2007 ‘ Natural fiber-reinforced polymer composites. Proc.Pakistan Acad Sci. Vol:44, No:2, pp:129-144
Saira taj, Munawar ali munawar and Shafiullah khan.2007 ‘Natural fiber-reinforced polymer composites’, Proc.Pakistan Acad Sci.Vol:44,No:2,pp:129-144
Sanadi, Anand Ramesh , Caulfield, Daniel.2008 ‘Thermoplastic polyolefins as formaldehyde free binders in highly filled lignocellulosic panel boards: using glycerine as a processing aid in kenaf fiber polypropylene boards’ vol.11, no.4, pp. 487-492. ISSN 1516-1439. Shinichi shibata, Takuya Kamiyama and Isao Fukumoto.2006. ‘Effects of bamboo and kenaf fiber on the mechanical properties of lightweight porous composites’ GPEC2006 paper abstract # 13B
Shinji Ochi ,2008, ‘Mechanical properties of kenaf fibers and kenaf/ PLA composites’ Mechanics of material Vol:40, pp: 446-452
Shinji Ochi, 2008, ‘Mechanical properties of kenaf fibers and kenaf/ PLA composites’ Mechanics of materials Vol:40, pp.446-452
Siew kim Tan, Sahrim Hj.Ahmad, Chia, chin Hua & Syed Yusainee Yahya. 2009 ‘ Rubber toughened epoxy filled with kenaf fiber composites’ Malaysia polymer International conference.
Siew kim Tan, Sahrim Hj.Ahmad, Chia, chin hua, Syed yusainee yahya,2009 ‘Rubber toughened epoxy filled with kenaf fiber composites’ Malaysia polymer international conference (MPIC 2009)
Singha a.s,Vijay kumar thakur, 2009 ‘Synthesis and characterization of short saccaharum cilliare fiber reinforced polymer composites’ E-journal of chemistry, Vol:6, No.1,pp:34-38
167
Singha Amar S. and Vijay Kumar Thakur, 2009, ‘Study of mechanical properties of urea-formaldehyde thermosets reinforced by pine needle power’
Structures, vol. 75, no. 1-4, pp. 520 – 523
Suffian M, GA Ormondroyd, MD Hale, 2009, ‘Comparisons of particleboard produced from acacia hybrid and a UK commercial particleboard furnish from recycled wood’ Journal of tropical forest science Vol:22, No:3,pp: 227-236
Taghi Tabarsa, Alireza Ashori, Maria Gholamzadeh, 2011 ‘ Evaluation of surface roughness and mechanical properties of particleboard panels made from bagasse’ Composites: part B Vol:42,pp:1330-1335 Tajvidi Mehdi, 2004 ‘ static and dynamic mechanical properties of a kenaf fiber-wood flour/polypropylene hybrid composite’ Journal of applied polymer science, vol.98,pp: 665-672, DOI: 10.1002/app.22093
Takashi Nishino, Koichi Hirao, Masaru Kotera, Katsuhiko Nakamae, Hiroshi Inagaki,2003, ‘Kenaf reinforced biodegradable composite’, Composites science and technology Vol:63,pp:1281-1286
Terence Tumolva, Masatoshi Kubouchi, Saiko Aoki, Tetsuya Sakai, 2010 ‘Effect of fiber loading on the mechanical strength of NFR hybrid composites’ AJChE2010, Vol :10,No.1, pp.22-27
Teresa Garcia-ortuno, Javier andreu-rodriguez, Maria T. Ferrandez-garcia, Manuel ferrandez-villena and clara. E.Ferrandez-Garcia,2011 ‘Evaluation of physical and mechanical properties of particleboard made from giant reed (Arundo Donax L.) 2011, particleboards from giant reed’, Bioresources Vol:6, No:1, pp:477-486
Teresa Garcia-Ortuno, Javier Andreu-Rodriguez, Maria T.Ferrandez-Garcia, Manuel Ferrandez-villena , Clara. E. Ferrandez-garcia, 2011 ‘ Evaluation of the physical and mechanical properties of partivcleboard made from giant reed’ BioResources Vol:6, No:1, pp.477-486
Turner, H.D,1954 ‘Effect of particle size and shape on strength and dimensional stability of resin bonded wood-particle panels’,For. Prod.J. Vol:4,No:5,pp:210-222
Wang W, Yan N.2005 ‘Characterizing liquid resin penetration in wood using a mercury intrusion porosimeter’, wood and fiber science Vol:37,No.3, pp:505-513
Wong KJ, Umar Nirmal, BK Lim, 2010 ‘Impact behavior of short and continuous fiber-reinforced polyester composites’ Journal of reinforced plastics and composites 2010 29:3463, DOI: 10.1177/0731684410375639
168
Wong, E. D., Zhang, M., Wang, Q. and Kawai, S. 1999 ‘Formation of the density profile and its effects on the properties of particleboard’, Wood Science and Technology, vol. 33, pp.327-340 Xue Y, Du Y, Elder S, Shame D, Horstemeyer M, Zhang J. 2007 ‘Statistical tensile properties of kenaf fibers and composites’ In: Proceedings of the ninth international conference on wood and biofiber plastic composites, May 21-23 Madison WI
Y.Copur, C.Guler, M.Akgul, C.Tascioglu,2006, ‘Some chemical properties of hazelnut husk and its suitablebility for particleboard production’ Building and environment 42 (2007) pp.2568-2572
Yang Te-Hsin, Cheng-Jung Lin, Song-Yung Wang, Ming-Jer Tsai,2007 ‘ Characteristics of particleboard made from recycled wood-waste chips impregnated with phenol formaldehyde resin’ Building and environment 42, pp:189-195
Yaser Mirbagheri, 2010,’ Mechanical and physical properties of wood-plastic composite panels’, Journal of reinforced plastics and composites 2010 29:310.
Yasin Muhammad, Abdul Waheed Bhutto, Ahmed Bazmi, Sadia KArim,2010 ‘Efficient
utilization of rice-wheat straw to produce value-added composite products’ ,International
Journal of Chemical and environmental engineering, Vol.1 No.2
Yasin Muhammad, Abdul Waheed Bhutto, Aqeel Ahmed Bazmi, Sadia Karim, 2010 ‘Efficient utilization of rice-wheat straw to produce value-added composite products’ International journal of chemical and environmental engineering,Vol:1, No.2
Yibin Xue, Yicheng Du, Steve Elder, Kunpeng Wang, Jilei Zhang.2009 ‘Temperature and loading rate effects on tensile properties of kenaf bast fiber bundles and composites’ Composites : Part B:40:189-196
Young-Kyu Lee, Sumin Kim, Han-Seung Yang, Hyun-Joong Kim, 2003 ‘Mechanical properties of rice husk flour-wood particleboard by Urea-formaldehyde resin’ Mokchae Konghak Vol:31, No:3, pp : 42-49
Zheng Yi, Zhongli Pan, Ruihong Zhang, Bryan M. Jenkins, Sherry Blunk,2005 ‘Medium-density Particleboard from Saline Jose Tall Wheatgrass’ An ASAE Meeting Presentation
Zhongli Pan, Ruidong Zhang,Yi Zheng, Bryan M.Jenkins, Sherry Blunk,2005 ‘Properties of medium-density particleboard from saline athel wood’ An ASAE meeting presentation, paper number: 056128
169
Appendix
A.1 Real life Application :
Below are the particleboard which had fulfill the American National
Standard ANSI A208.1-2009.
Table A.1 Particleboard application
Raw Material Application Raw Material Application
Core 1mm PF
70 wt% M-1 Waste wood M-2
75 wt% M-S Bast LD-2
80 wt% M-S Core 1mm M-1
85 wt% M-1 Core 0.6mm LD-2
90 wt% M-2 500Kg/m^3 LD-2
Waste wood Density 500kg/m^3
70 wt% M1 70 wt% LD-1
75 wt% M5 75 wt% LD-2
80 wt% M2 80 wt% LD-2
85 wt% LD-2 85 wt% LD-1
90 wt% LD-1 90 wt% LD-1
Hybrid (1mm) Hybrid (0.6mm)
25% Core 75% waste
wood LD-2 25% Core 75% waste wood LD-2
50% Core 50% waste
wood H-3 50% Core 50% waste wood H-1,H-2
75% Core 25% waste
wood H-3 75% Core 25% waste wood M-3
Types of kenaf core fiber 75wt% Core 0.6mm
0.4mm H-3 70 wt% M-3
170
1mm M-5 75 wt% M-3
1.5-3 mm LD-1 80 wt% M-5
Bast
70 wt% LD-1,2
75 wt% LD-1,2
80 wt% LD-1,2
Table A. 2: General use and grades
Grade Use
M-1, M-S Commercial
M-2, M-3 Industrial
H-1, H-2, H-3 High density industrial
LD-1, LD-2 Door core
M-3 Interior stair tread
Figure A. 1: Prototype of the particleboard
171
A.2 Calculation:
TE
*81.9*= Dimensionless ( MOR, MOE, Tensile strength , Internal bonding & Young’s
modulus )
AJ
*81.9*= Dimensionless screw test
VF
*81.9*= Dimensionless impact strength
1. E = modulus (MPa)
2. T = thickness (m)
3. ρ = composite density kg/m3
4. J = Impact strength (KJ/m2)
5. A= Area (m2)
6. F= force (N)
7. V = volume (m3)
A.3 Result without Dimensionless:
Table A.3 : Actual value for the tests
Raw Material
MOR MOE IB
Screw.
T
Y.
Modulus
Tensile.
S Impact.S
N/mm^2 N/mm^2 N/mm^2 N N/mm^2 N/mm^2 J/m^2
Core 1mm
70% 20.62 1712.74 1.76 528.31 2686.68 5.52 53257.58
75% 22.58 2014.37 1.92 434.54 2727.30 11.00 12480.58
80% 21.49 1979.82 1.29 439.83 2643.53 8.62 8539.06
172
85% 17.62 1670.38 1.02 377.98 1861.50 6.06 5901.23
90% 14.84 1481.72 0.78 283.52 1364.12 5.42 5788.88
Core 0.6mm
70% 30.48 3095.31 0.96 473.85 3150.43 11.28 16481.08
75% 28.78 2720.99 1.61 458.68 3094.66 13.81 49087.51
80% 18.70 1910.30 0.43 356.37 2847.09 12.51 56205.00
85% 15.40 1453.85 0.33 254.07 1871.85 8.70 48684.30
90% 13.43 1358.07 0.28 233.17 1608.80 6.90 43005.03
Bast
50% 12.14 1908.09 0.28 388.19 1226.43 2.55 11609.64
60% 16.18 2295.07 0.28 500.47 2934.90 5.51 19245.13
70% 20.96 2927.07 0.31 497.06 2884.82 8.28 26880.62
75% 16.11 1899.43 0.32 409.20 2870.53 2.78 31835.33
80% 12.77 1276.96 0.34 353.84 2836.24 4.00 47650.96
85% 6.14 1130.98 0.04 342.01 2198.11 3.11 21899.26
90% 6.21 560.90 0.04 331.89 1559.98 7.16 8773.80
Waste wood
70% 20.62 1793.31 0.84 371.33 2200.73 8.35 24972.90
75% 22.58 1979.76 0.95 413.57 2507.57 7.32 20058.50
80% 21.49 2367.93 1.67 560.78 2595.18 8.37 18613.87
85% 17.62 1271.73 0.79 279.44 1992.38 2.81 17169.25
90% 14.85 932.20 0.29 256.61 1061.91 3.77 44262.91
PF
Waste wood 20.78 2103.80 0.76 501.79 1123.90 13.24
140903.0
3
Bast 15.43 1809.36 0.29 526.48 1369.58 8.50
148067.3
1
Core 1mm 13.38 1602.54 0.75 323.14 1251.90 5.65 57354.26
Core 0.6mm 15.49 1324.98 1.13 374.62 1425.65 7.04
162710.7
5
173
500Kg/m^3 13.57 1270.05 0.75 258.34 1041.63 4.42 37531.19
Density
500kg/m^3
70% 8.20 1006.61 0.46 244.05 1169.44 3.55 13266.27
75% 10.03 1097.76 0.49 314.77 1187.06 5.07 10843.31
80% 13.17 1408.46 0.93 358.93 1439.00 6.59 51103.64
85% 11.19 909.35 0.65 281.48 1124.36 5.21 40845.28
90% 9.57 866.74 0.53 265.59 872.58 3.83 31857.13
Hybrid (1mm)
25% Core 75%
waste wood 8.41 1059.29 0.40 139.17 886.75 1.59 98326.36
50% Core 50%
waste wood 39.11 3087.20 1.00 354.63 2518.99 7.25
121936.7
4
75% Core 25%
waste wood 25.93 4005.54 1.47 451.95 2373.01 8.46 77868.26
Hybrid (0.6mm)
25% Core 75%
waste wood 12.05 1579.58 1.22 418.60 1830.50 2.91
103627.6
6
50% Core 50%
waste wood 30.99 2683.03 1.17 371.60 2754.63 4.92
128715.0
9
75% Core 25%
waste wood 26.83 3604.16 0.58 346.53 2535.63 8.31
148234.1
7
Types of kenaf
core fiber
0.4mm 12.11 3207.60 1.33 369.10 2366.95 7.54 85405.33
0.6mm 28.78 2720.99 1.61 458.68 3094.66 13.81 49087.51
1mm 22.58 2014.37 1.92 434.54 2727.30 11.00 12480.58
>1.5-3 mm 13.54 917.12 0.96 238.75 1609.58 2.92 15454.30
174
Published Paper
Tay Chen Chiang, Saad A, Mutasher, Nazim Mir-Nasiri, 2012 ‘THE EFFECT OF BOARD DENSITY ON THE PROPERTIES OF KENAF CORE FIBER UREA FORMALDEHYDE PARTICLE BOARD’Engineering Towards Change - Empowering Green Solutions 2012Kuching ,Sarawak, Malaysia, 10 -12 July 2012
Tay Chen Chiang, Saad A, Mutasher, Nazim Mir-Nasiri, Alyssa, Wong Cing. 2011‘KENAF FIBRE UREA FORMALDEHYDE RESIN COMPOSITES’Regional Symposium On Engineering & Technology 2011
