1st International Conference on Engineering Materials and ... · Sawdust is a good representative of abundant residual forest biomass consists of 40–50% cellulose, 25– ... okra,

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Proceedings of the

1st International Conference on Engineering Materials and Metallurgical Engineering

22- 24 December, 2016 Bangladesh Council of Scientific and Industrial Research (BCSIR)

Dhaka, Bangladesh

EFFECT OF CHEMICAL TREATMENT OF SAWDUST ON THE INTERFACIAL AND MECHANICAL PROPERTIES OF POLYPROPYLENE COMPOSITES

M. MahmudurRahmana, M.A. Gafurb, G. M. ArifuzzamanKhana, M. Hasanuzzamana, M. ShamsulAlama*, S. M. AbdurRazzaquea

aDept. of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, Bangladesh

bPP and PDC, BCSIR, Dhaka, Bangladesh

ABSTRACT Biomass provides valuable raw materials not only for energy but also achieve the goal of sustainable development by converting into various lifesaving, decorative, structural and non-food consumer products such as pharmaceuticals, paints, adhesives, textile products, cosmetics, papers and various commodity specially polymer composites. Sawdust is a good representative of abundant residual forest biomass consists of 40–50% cellulose, 25–35% hemicellulose and 20–30 % lignin, approximately. In the present work, saw dust fiber reinforced polypropylene (PP) composites were prepared by simple hot press molding method. The chemically modified saw dust fiber by means of NaOH, KMnO4, NaClO2, acetic anhydride and n-substituted metharylamide were used with 0, 5, 10 and 20 wt% in respect of matrix used in composites. The composites are characterized by tensile properties, water absorption test and SEM analysis. In terms of mechanical properties the tensile modulus increased, whereas the tensile strength and elongation at break decreased for all types of composites. Morphological examination of the fracture surfaces were carried out by SEM in order to investigate the variation of the measured mechanical properties revealed presence of microvoids resulting from weak filler-matrix interfacial adhesion. Keywords: Sawdust, Chemical Treatment, Composites, Mechanical Properties

1.INTRODUCTION

There is a growing interest in the use of natural fibre as reinforcing component for both thermoplastic and

thermoset because of the benefits such as renewable and environment friendly. The abundance of natural fibre combined with the ease of its process ability is an attractive feature, which makes it a substitute for synthetic fibre that is potentially toxic. Many studieshave been made on the potentials of the natural fibres as reinforcing components for plastic materials[1-2]. Natural fibre reinforced thermoplastic composites form a new class of materials, which seem to have good potential in the feature as a substitute for wood based material in many applications. However, lack of good interfacial adhesion and poor resistance to moisture absorption makes the use of natural fibre reinforced composites less attractive. Various fibresurface treatments like mercerization, isocyanate treatment, acrylation, latex coating, permanganate treatment, acetylation, silane treatment and peroxide treatment have been carried out which results in improving composite properties [3-6]. Interfaces play an important role in the physical and mechanical properties of composites. Reinforcing fibres are normally modified by surface treatments to improve their compatibility with the polymer matrix.

Among the chemical modifications, alkali treatment is most popular. Alkali treatment leads to the increase in

the amount ofamorphous cellulose at the expense of crystalline cellulose.The important modification occurring here is the removalof hydrogen bonding in the network structure. Alkali treatment is even considereda standard step to increase the efficiency of any further treatment [7-8]. Bleaching is generally used in tensile application of natural fibre. However, it is very efficient methods to remove lignin from natural fiber. Khan et al. used sodium chlorite bleaching agent for the surface treatment of jute, banana, okra, pineapple leaf fibres on their different studies [9-10]. Fibre surface modification by KMnO4 increases the nucleating ability and thermal properties of natural fiber PP composites [11].Acetylation is a rather attractive method of modifyingthe surface of natural fibers and making it more hydrophobic.It has been shown to reduce swelling of wood in waterand has been studied more than any other chemical reactionof lignocellulosic materials. The main principle of themethod is to react the hydroxyl groups (OH) of the fiberwith acetyl groups (CH3CO), therefore rendering the fibersurface

Proceedings of the 1st ICEMME, 22-24, Dec, 2016, Dhaka, Bangladesh

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more hydrophobic [12-13]. Graft copolymerization through vinyl monomers often employed to improve surface properties of natural fibres. Methacrylamide (MA) grafting is not only used to modify fibre surface but alsothe thermoplastic matrix to achieve better interfacial bonding andmechanical properties in composites [14-17].

In the present investigation, our main objective is to determine the suitability of saw dust fibre as

reinforcement in the PP matrix. A systematic study of the mechanical properties of the composites as a function of fibre loading, NaOH, NaClO2, KMnO4, acetic anhydride and n-substituted methacrylamide treatments have been made to achieve better mechanical properties.

2. MATERIALS AND METHODS

2.1 MATERIALS

Commercial grade polypropylene (Merck, Germany) was used as a matrix without further purification. Saw dust fiber was used as reinforcing agents obtained from local saw mill of Kushtia district, Bangladesh. The fibre was scoured with a solution containing 3.5 g/L Na2CO3 and 6.5 g/L detergent at 70°C in a large beaker.

2.2 CHEMICAL TREATMENTS

The scoured fibre was bleached with 7 g/L NaClO2 solution buffered to pH 4 at 90-95ºC for 90min

maintaining fibre to liquor ratio 1:50. The fibre was then treated with 2% Na2S2O5 solution for 15min to reduce chlorite action and washed thoroughly with distilled water [4].

Fibre bundles were soaked in 10% NaOH (pH 12.8) solution for 10 h and then neutralized with 1%

CH3COOH. Fibres were then washed with deionized water. Subsequently, the fibres were dried at 50°C for 24 h [4].

A small amount of alkali-treated fibre was dipped in KMnO4 solution in acetone for 10 min. Potassium

permanganate solution of 0.5% concentration was used in the presence of 1 to 2 drops of concentrated H2SO4 and stirred for certain duration. Finally, the fibre was washed in distilled water and dried for further use [4].

10 g fibre was soaked in glacial acetic acid for 1 h at room temperature. The acid was then decanted and

soaking was continued in 10% (CH3CO)2O that contains two drops of concentrated H2SO4 for 10 min. The fibre was separated using a buchner funnel, washed with water and dried in an air circulation oven at 50◦C for 24 h [4].

n-substitutedmetharylamide (nMA) monomer was taken in cold distilled water. The grafting bath was

prepared by 1% nMA monomer, 0.01% K2S2O8 and 0.01% FeSO4. Grafting reaction was carried out at 90°C for 60 min. During grafting the bath was stirred occasionally by a glass rod and allowed to stand for further 30 min till it cools down. The fibre to liquor ratio was maintained at 1:50. Hot distilled water was then added in grafting bath to compensate the loss of water. After grafting the fibre was washed with hot distilled water and CH3OH to remove the adhering homopolymer and dried at room temperature [18].

2.3 COMPOSITES PREPARATION

The fibres were put in an oven at 70oC for 24 h. Composites were prepared by compounding PP matrix with

the untreated and treated fibres in a compress molding machine. Predetermine amount of PP pellets and dried fibres were taken in a stainless steel mold and placed in molding machine. A mold release spray was used for easily taking composite from mold. During composite fabrication 50 KN pressure was fixed and mold was heated at 170oC for 30 min. Mold was then suddenly cooled by tap water. Finally composite sample was taken out from mold and sized for tensile measurement. The specimens for tensile (dimensions: 110×15×3)mm3 tests were made using a cutting machine. The quantities of untreated and treated fibres were varied from 5 to 20% in weight in order to study the effect of fiber loading [19].

2.4 MEASUREMENTS


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The tensile tests were conducted according to ASTM D882 (2012) using a Universal Testing Machine (Hounsfield UTM 10KN, UK). The clamping length for each specimen on each jaw was 15 mm and no extensometer was used for the tensile tests. The tests were performed at a crosshead speed of 5 mm/min [8].

SEM micrographs of fiber surface and cross sections of untreated and treated fibers were taken using a

scanning electron microscope JEOL 6400 (USA). Prior to SEM evaluation, the samples were coated with gold by means of a plasma sputtering apparatus.

The extent of water absorption of both untreated and treated fibre composites was determined as per

ASTM-D-570. The specimens (dry weight W1) were subjected in water at 50°C for 24 h,and the final conditioned weight (W2) was determined. Percentage of water absorption was calculated as follow:

Water absorption=

ௐమషೈభௐభ

× 100

3. RESULTS AND DISCUSSION The tensile strength (TS) of molded composites using 0, 5, 10 and 20 wt% untreated fibre is illustrated in

Table 1. Among the various fibres loading maximum TS is found highest in 10% fibre loading. The fewer amounts of fibres are finely distributed and the interfacial bonding between the fibre and matrix is good. After 10% fibre addition, the tensile strength decreases. This is probably due to incompatibility of the fibre within the matrix, which promoted microcrack formation at the interface as well as non-uniform stress transfer due to fibre agglomeration in the matrix[20]. Tensile modulus (TM) was calculated from tangent of initial point of tensile stress-strain curves (Fig. 1). It has been also seen that TM increases and elongation percentage decreases with the increase of fiber loading. This proves the fiber gives stiffness of composite samples[19].

Table 1: Effect of fiber content on tensile properties of composites

PP : saw dust fiber

Tensile Strength (MPa) Tensile Modulus (GPa) Elongation (%)

100:0 76.2 4.11 11.0 95:5 83.0 5.42 6.6

90:10 88.7 6.67 4.7 80:20 62.5 7.61 3.4

The effects of chemical treatment of saw dust fiber on the tensile properties are listed in Table 2. The

bleached saw dust fiber reinforced PP composite shows a slight reduction in TS in comparison to untreated fibre composites. This is attributed to lowering of the fibre tensile strength due to loss of the cementing material lignin, which results in a decrease in TS of saw dust fiber reinforced PP composites. Alkali treatment improves the tensile properties of a composite, whichis attributed to the increased mechanical interlocking between alkali treated fibres and PP matrix.This may be due to the increase in surface roughness of the fibre as a result of leaching out of alkali soluble components such as lignin, wax and fatty acids etc. It is also obvious that the tensile properties of PP composites with acetylated fiber are higher than those of the untreated composites. The improvement in tensile properties of treated fibre composites is attributed to the presence of —CH3 groups in acetylated fibre, which paves the way for its better interaction with PP. Table also represents the effect of nMA grafting onto saw dust fibres on TS of the resulting composites. While studying grafting effect of untreated composite is taken as standard material for comparison. In case of nMA grafted fiber composites, TS increase by 11.2%. The improved TS of nMA grafted fibre composites may be due to better wet ability and adhesion between the grafted fibres and the matrix polymer. TM of fiber reinforced composite shows similar trend like TS while treatment has no effect on elongation properties of composites.


105

0 1 2 3 4 5 60

100

200

300

400

500

600

Stre

ss (N

)

Strain (%)

ab

c

d

e

f

FIG. 1: TENSILE STRESS-STRAIN CURVES OF 10WT% FIBER LOADED COMPOSITES (a)

UNTREATED, (b) ALKALI TREATED, (c) BLEACHED, (d) KMNO4 TREATED (e) ACETYLATED AND (f) nMA TREATED FIBER

FIG. 2: TENSILE PROPERTIES OF 10WT% FIBER LOADED COMPOSITES

80

85

90

95

100

Tens

ile s

tren

gth

(MPa

)

0123456789

Tens

ile M

odul

us (G

Pa)

4

4.5

5

5.5

Elon

gatio

n (%

)


106

Table 2: Effect of fiber treatments on the properties of composites

FIG. 3: SEM IMAGES OF FRACTURE SURFACES OF SAW DUST FIBERS PP COMPOSITES: (a) UNTREATED, (b) ALKALI TREATED, (c) BLEACHED, (d) KMNO4 TREATED (e) ACETYLATED AND (f) nMA TREATED FIBER The water absorption behavior of untreated and treated fiber-PP composites is listed in Table 2 and Fig. 2.The extent of water absorption decreases considerably on acetylation and nMA grafting of fibres. nMA grafted fibre

Saw dust/PP Composites Tensile Strength (MPa)

Tensile Modulus (GPa) Elongation (%) Water absorption

(%)

Untreated 88.7 6.67 4.7 4.2 Alkali-treated 94.5 7.91 4.5 4.0 Bleached 86.3 6.63 4.8 4.1 KMnO4 treated 89.1 6.72 4.7 3.9 Acetylated 91.8 7.76 5.1 2.3 nMA treated 98.6 8.08 5.2 2.1


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shows considerable reduction in water absorption (2.1%) confirms a better adhesion between nMA grafted fibre with PP. In case of surface modified saw dust fibre composites, the fibres are masked with the PP in the laminate with a stronger adhesion resulting in greater hydrophobicity and lesser water absorption. The water absorption of alkali treated, KMnO4 treated and bleached fiber-PP composites are slightly less than the untreated fiber-PP composites. From SEM images of raw and treated fibers PP composites, it is clearly observed that fracture surfaces of raw Surface morphology analysis of untreated and treated fibers PP composites. Fig. 3(A) shows that the interaction between the fiber and PP matrix in composites is very week, due to poor fiber-matrix compatibility which causes these voids to become a number of micro crackles. The main reason might be huge difference of surface energy between untreated fiber and PP matrix Fig. 3 (B,C, D E, and F) show the interfacial adhesion between fibers and PP matrix is strong compared to fig. (A), which results in less number and small size of voids around fiber surfaces, good fiber wetting and interlocking than that exhibited by untreated fiber composite. The interfacial adhesion between fibers and PP matrix is quite strong which results good fiber wetting and interlocking, no bigger size pores, no fibers pull out from composite.

4. CONCLUSION

The adhesion between untreated saw dust and PP matrix is poor.The properties of composites were varied with fiber loading. 10 wt% fiber loaded composite exhibited highest tensile strength. The modification of the fibre surface increases the mechanical properties of composites. Among the treated saw dust fibre reinforced PP composites, nMA grafted fiber composite shows better tensile strength, tensile modulus and elongation at break. nMA grafted fiber composites showed 11.2% increase in tensile strength compare to untreated fibre composite.Bleached, alkali treated, KMnO4 treated and acetylated saw dust fiber composites also show better tensile strength and modulus than untreated fibre composites.

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1st International Conference on Engineering Materials and ... · Sawdust is a good representative of abundant residual forest biomass consists of 40–50% cellulose, 25– ... okra,