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CHAPTER 1
INTRODUCTION
1.1 GENERAL
Global technical development depends ultimately on the effective
utilization of the existing and new materials. The new materials may be the
combination of two or more components to cater for particular needs. The
composite materials come under this category. Composite materials are the
macroscopic combination of two or more distinct materials with enhanced
properties. The aim of using the composite material is for high strength to
weight ratio and to meet the applications with specific properties. Fibers are a
class of hair-like materials that are continuous filaments or discrete elongated
pieces. Fiber-reinforced composite materials consist of fibers of high strength
and modulus which are bonded in a matrix. The fiber has better interface with
the matrix. In composites, both fibers and matrix retain their physical and
chemical identities. But they produce a combination of properties that cannot
be achieved either by fiber or matrix when they are used alone. In general,
fibers are the principal load-carrying members.
The matrix in a composite serves the following purpose,
Keep the fibers in the desired location and orientation.
Act as a load transfer medium.
Protect the fibers from the environmental damage like
temperature and humidity.
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Historical examples of composites are plentiful in the literature.
Plywood (invented by the Egyptians, approx. in 1500 BC) and reinforced
concrete (invented by the Romans, approx. 1000 BC), also natural fiber
reinforced clay (used by men before iron was invented) are in essence of
composite materials. The composite bows comprising of bark, sinew, bone,
wood, horn, metal and glues are believed to have appeared in the hands of
Assyrian archers as early as 1800 BC. Assyrians warred with the Egyptians,
Babylonians and other civilizations and used the power of the composite
bows to make a significant impression on their rivals. The modern era of
composites did not begin until scientists developed plastics. Until then,
natural resins derived from plants and animals were the only source of glues
and binders. In the early 1900s, plastics such as vinyl, polystyrene, phenolic
and polyester were developed. These new synthetic materials out performed
resins that were derived from nature. However, plastics alone could not
provide enough strength for structural applications. Reinforcement was
needed to provide the strength and rigidity. In 1935, Owens Corning
introduced the first glass fiber, fiberglass. Fiberglass, when combined with a
plastic polymer creates an incredibly light weight and strong structure. The
first commercial composite boat hull was introduced in 1946.
This is the beginning of the Fiber Reinforced Polymer (FRP)
industry. In the 1970s, the composites industry began to mature. Better plastic
resins and improved reinforcing fibers were developed. Kevlar fiber has
become the standard in armor due to its high tenacity. Carbon fiber was also
developed around this time and it is a promising replacement for metal as the
new material of choice. The composite materials find application in
aerospace, automobile industry, marine vessels, structures, building,
construction industry, chemical plants, corrosion resistant products, consumer
durable products, sports goods etc.,
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The composites industry is still evolving with much of the growth
and focused around renewable energy. Additionally, composites are on the
path towards being more environmentally friendly. Resins will incorporate
recycled plastics and bio-based polymers. The synthetic fibers pollute the
environment since they are not biodegradable. Development of natural fibers
reinforced composites is highly attractive. Composites are materials made
from a binder, usually a resin and a reinforcement fiber. Composites in which
the resin and/or fiber are made from renewable resources are often called
bio-composites.
Issues such as recyclability and environmental safety are becoming
increasingly important in the introduction of materials and products. Natural
fibers have a number of techno-economical and ecological advantages over
synthetic fibers like glass fiber. Combination of interesting mechanical and
physical properties together with their environmentally friendly character has
created interest in a number of industrial sectors, notably the automobile
industry.
Glass and carbon fibers have been used widely as reinforcement
materials, but their non-recyclability becomes a significant disadvantage at
the end of their lifetime. They are also found to be hazardous to health. The
natural composites can be very cost-effective material especially for
building & construction of industrial panels, false ceilings, partition boards
etc, packaging, automobile, railway coach interiors and storage devices. It
helps to make the best quality industrial yarn, fabric, net and sacks. Wind
turbine blades are constantly pushing the limits on size and are requiring
advanced materials, designs and manufacturing. In the future, composites will
utilize even better fibers and resins, many of which will incorporate nano-
materials. The research activities will continue to develop improved materials
and ways to manufacture them into products.
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In spite of these advantages the natural fibers have some limitations
and they need to be overcome to make it competitive to the synthetic fibers.
The transition towards a bio-based economy and sustainable development as a
consequence of global warming offers high prospects for natural fiber
reinforced bio-composite materials. Changing to a bio-based economy
requires substitution of common raw materials from renewable (plant and
animal based) resources. It will help to improve cultivation of fiber plants and
also economy of the country.
1.2 NATURAL FIBERS AND THEIR SIGNIFICANCE
Natural fibers can be defined as bio-based fibers of vegetable and
animal origin. This definition includes all natural cellulosic fibers (cotton,
jute, sisal, coir, flax, hemp, abaca, ramie, etc.) and protein based fibers such
as wool and silk. Practically in all countries natural fibers are produced and
used to manufacture a wide range of traditional and novel products from
textiles, ropes, nets, brushes, carpets, mats, mattresses to paper and board
materials. The growing environmental concern on global warming have
inspired the automobile, structural, construction, packing industries etc., to
search for sustainable materials that can replace conventional synthetic
polymeric fiber. Natural fibers seem to be a good alternative since they are
readily available in fibrous form and can be extracted from plant leaves at
very low costs. Natural fibers are subdivided based on their origins, coming
from plants, animals or minerals. Generally, plant or vegetable fibers are used
to reinforce plastics. Various research works are being carried out with the
natural fibers like bamboo, coir, jute, flax, sun hemp, ramie, kenaf, roselle,
straw, rice husk, sugar cane, grass, raphia, papyrus and pineapple leaf fibers.
A single fiber of all plant based natural fibers consists of several cells. These
cells are formed out of crystalline micro fibrils based on cellulose, which are
connected to a complete layer, by amorphous lignin and hemicellulose. Many
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of such cellulose-lignin/hemicellulose layers in one primary and three
secondary cell walls stick together to a multiple layer composites. These
fibers are called lingo-cellulosic fibers. The natural fibers are classified as
shown in Figure 1.1.
1.3 TYPES OF NATURAL FIBERS
Natural fibers are available from plant, animal and mineral sources.
Natural fibers can be classified according to their origin. Animal fibers
generally contain proteins such as collagen, keratin and fibroin. Examples for
the animal fiber are Alpaca, Angora, Byssus, Camel hair, Cashmere, Catgut,
Chiengora, Guanaco, Human hair, Llama, Mohair, Pashmina, Qiviut, Rabbit,
Silk, Sinew, Spider silk, Wool, Vicuna, Yak etc. Mineral fibers can be
particularly strong because they are formed with less number of surface
defects, asbestos is a common one. The plant based fibers are known as
vegetable fibers. They mainly contain cellulose in their structure. The
examples include cotton, jute, flax, ramie, sisal, and hemp etc., The natural
fibers can be further categorized into the following classification.
1.3.1 Fruit / Seed Fibers
The fruits and seeds of plants are often attached to hairs or fibers or
encased in a husk that may be fibrous. These fibers are cellulosic based and
having commercial importance. Cotton, the most important natural textile
fiber is one among such type. Coir or coconut fiber belongs to the group of
hard structural fibers. It is an important commercial product obtained from the
husk of the coconut. Seed fiber is applied in less demanding applications such
as stuffing of upholstery. Coir is used to make ropes, mats and brushes.
Borassus fruit fibers which are lingo cellulosic in nature are extracted from
the Borassus fruits. The fleshy substance of the fruit is reinforced by the
Borassus fruit fibers.
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1.3.2 Leaf Fibers
Leaf fibers are obtained from leaves of plants (flowering plants that
usually have parallel-veined leaves, such as grass, lilies, orchids and palms),
used mainly for cordage. The fiber generally traverses the length of the leaf
and is often the densest near the leaf undersurface. Such fibers are usually
long and stiff. The leaf elements are harvested by cutting at the base with a
sickle-like tool and bundled for processing by hand or by machine
decortications. In the latter case, the leaves are crushed, scraped, and washed.
The fibers are generally coarser than the bast fibers. Commercially useful leaf
fibers include abaca, cantala, henequen, sisal, banana, agave etc.
1.3.3 Bast Fibers
Bast fiber or skin fiber is plant fiber collected from the skin or bast
surrounding the stem of certain, mainly dicotyledonous plants. They support
the conductive cells of the phloem and provide strength to the stem. In the
phloem, bast fibers exist in bundles that are glued together by pectin. The
retting process separates the valuable fibers in the phloem. Often bast fibers
have higher tensile strength than other kinds and are used in high-quality
textiles. Most of the technically important bast fibers are obtained from herbs
cultivated in agriculture, as for instance flax, hemp, kenaf and ramie.
1.3.4 Stalk Fibers
Fibers are actually the stalks of the plant. e.g. straws of wheat, rice,
barley and other crops including bamboo and grass. Tree wood is also such a
fiber. The stalk of the plant contains two types of fiber, the outer bast fiber
which can be processed into long strands and the inner woody core or hurds,
which are typically processed into material resembling wood chips. They are
used as reinforcing members in composites.
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Natural fibers
Plant fibers Animal fibers Mineral fibers
Silk
Wool
Animal hairs
Asbestos
Ceramics
Fruit/Seedfibers
Leaf fibers Bast fibers Stalk fibers
Examples:Cotton fibers, Coir fibers
Borassus fruit fibers,Tamarind fruit fibers,
Arecanut husk fibers etc.
Examples:Abaca fibers, Cantala
fibers, Henequenfibers, Sisal fibers,
Banana fibers, Agavefibers etc.
Examples:Flax fibers, hemp fibers,
kenaf fibers, Abacafibers, Jute fibers, Ramie
fibers etc.
Examples:Straws of wheat, rice,barley and other crops
including bamboo,grass, wood. etc.
Figure 1.1 Classification of natural fibers
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Table 1.1 Mechanical properties of synthetic fibers Mueller (2003)
FiberDensity
(g/cm3)
Diameter
(µm)
Tensilestrength(MPa)
Young’smodulus
(GPa)
Elongation
at break(%)
E-glass 2.5 5-25 2000-3500 70.0 2.5
S-glass 2.5 3-25 4570 86.0 2.8
Aramide(normal)
1.4 10-12 3000-3150 63.0-67.0 3.3-3.7
Carbon 1.4 5-10 4000 230-240 1.4-1.8
Table 1.2 Mechanical properties of natural fibers Malkapuram (2008)
FiberDensity
(g/cm3)
Diameter
(µm)
Tensilestrength(MPa)
Young’smodulus
(GPa)
Elongation
at break(%)
Jute 1.3-1.45 25-200 393-773 13-26.5 1.16-1.5
Hemp - - 690 - 1.6
Kenaf - - - - 2.7
Flax 1.5 - 345-1100 27.6 2.7-3.2
Ramie 1 - 400-938 61.4-128 1.2-3.8
Sunn - - 690-1000 - 5.5
Sisal 1.45 50-200 468-640 9.4-22.0 3-7
Cotton 1.5-1.6 - 287-800 5.5-12.6 7-8
Kapok - - - - 1.2
Coir 1.15 100-450 131-175 4-6 15-40
Banana - - 540 - 1.5-9.0
PALF - 20-80 413-1627 34.5-82.5 1.6
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Table 1.3 Chemical composition of natural fibers Malkapuram (2008)
Fiber Cellulose(wt%)
Lignin
(wt%)
Hemi
Cellulose
(wt%)
Pectin
(wt%)
Wax
(wt%)
Moisture
Content
(wt%)
Jute 61-71.5 12-13 13.6-20.4 0.4 0.5 12.6Hemp 70.2-74.4 3.7-5.7 17.9-22.4 0.9 0.8 10Kenaf 31-39 15-19 21.5 - - -Flax 71 2.2 18.6-20.6 2.3 1.7 10
Ramie 68.6-76.2 0.6-0.7 13.1-16.7 1.9 0.3 8Sunn 67.8 3.5 16.6 0.3 0.4 10Sisal 67-78 8-11 10.0-14.2 10 2.0 11
Henquen 77.6 13.1 4-8 - - -Cotton 82.7 - 5.7 - 0.6 -Kapok 64 13 23 23 - -Coir 36-43 41-45 10-20 3-4 - 8
Banana 63-67.6 5 19 - - 8.7PALF 70-82 5-12 - - - 11.8
1.4 BENEFITS OF NATURAL FIBERS
High specific strength to weight ratio.
It is a renewable resource and less energy is used in the
extraction of fibers.
Minimum production cost.
No wear of tooling and skin irritation during extraction.
Good thermal and acoustic insulating properties.
They are durable, eco-friendly and bio-degradable.
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1.5 LIMITATIONS OF NATURAL FIBERS
Supply and demand cycles are based on product availability
and harvest yields.
Moisture absorption, which causes swelling of the fiber.
Quality variations based on growing sites and seasonal factors.
Restricted maximum processing temperature.
Low durability and poor fire resistance.
1.6 POLYMER MATRIX MATERIALS
The role of the matrix in a fiber-reinforced composite are: (1) to keep
the fibers in the desired location, (2) to keep the fibers in the desired
orientation (3) to transfer stresses between the fibers, (4) to provide a barrier
against an adverse environment, such as chemicals, moisture and to protect
the surface of the fibers from mechanical degradation (e.g. by abrasion). The
matrix plays a minor role in the tensile load carrying capacity of a composite
structure. But the selection of a matrix has a major influence on the
compressive, interlaminar shear as well as in-plane shear properties of the
composite material. The matrix provides lateral support against the possibility
of fiber buckling under compressive loading, thus influencing the
compressive strength of the composite material. The interaction between
fibers and matrix is also important in designing damage-tolerant structures.
The processing and defects in a composite material depend strongly on the
processing characteristics of the matrix. Polymer matrix is a long chain
molecule containing one or more repeating units of atoms joined together by
strong covalent bonds for which classification is shown in Figure 1.2.
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Figure 1.2 Classification of polymers
1.6.1 Thermoset Polymers
The molecules of the thermoset polymers are chemically joined
together by cross-links, forming a rigid, three-dimensional network structure.
Once these cross-links are formed during the polymerization reaction (also
called the curing reaction), the thermoset polymer cannot be melted by the
Polymers(Long chain molecules)
Plastics(Rigid Materials)
Rubbers(Flexible Materials)
Vulcanized Rubbers
Thermo PlasticElastomers
Thermoplastics(Uncross linked-Heat revesible)
Thermoset plastics(Cross linked – Rigid)
Examples:Polyamides, Acrylics,Polycarbonates,Polyethylene, ABS,Poly Vinyl Chloride,Poly Ether EtherKetone etc.,
Examples:Epoxy, Polyester resin,Melamineformaldehyde, Phenolformaldehyde, Vinylester, Cynate ester,Furans etc.,
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application of heat. But they may degrade if the temperature is high enough to
break the molecular chains. Polyester, Vinyl ester, epoxies, cross linked
acrylics, Phenolics, Polyurethanes, Furans, Polyimides etc., are the most
commonly used thermoset materials used in making the composites.
Thermosets are generally brittle and addition of fiber can improve
their toughness. They have good creep resistance. Toughness can also be
improved by blending elastomers into the thrmosets. Good wet out between
the fiber and the matrix can be attained without the aid of either high
temperature or pressure. Thermoset polymers are having better thermal
stability and chemical resistance. Thermoset PMC are being made and used
for the last forty years and they find applications in a wide range of products
ranging from aircraft, satellites, rockets, automobiles, machine elements and
consumer goods.
1.6.2 Epoxy Resin
The epoxy matrix consists of three member ring having one oxygen
atom and two carbon atoms in its chemical structure. The epoxy resins
contribute to the strength, durability and chemical resistance of the composite.
Epoxy is a copolymer and is formed from two different chemicals. These are
referred to as the resin and the hardener. The resin consists of monomers or
short chain polymers with an epoxide group at either end. Most common
epoxy resins are produced from a reaction between epichlorohydrin and
bisphenol-A, though the latter may be replaced by similar chemicals. Each
NH group can react with an epoxide group from distinct prepolymer
molecules, so that the resulting polymer is heavily cross linked and is thus
rigid and strong. The process of polymerization is called curing and can be
controlled through temperature, choice of resin and hardener compounds. The
structure of epoxy resin is shown in Figure 1.3
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Figure 1.3 Structure of epoxy
1.6.2.1 Hardeners
The hardener consists of polyamine monomers, for example
triethylenetetramine. When these compounds are mixed together, the amine
groups react with the epoxide groups to form a covalent bond. Amine
hardeners react with the epoxy resins, contributing to the ultimate properties
of the cured epoxy resin system. Amine hardeners provide: gel time, mixed
viscosity, demould time of the epoxy resin system. Physical properties such as
tensile, compression, flexural properties, etc., of the epoxy resin system are
also influenced by epoxy hardeners. The performance of epoxy hardeners in
the epoxy resins system depend on the chemical and physical characteristics
of the epoxy. The chemical characteristics of the epoxy resins that influence
epoxy hardeners are: viscosity and kind of diluents and fillers in epoxy resins.
The physical characteristics of the epoxy resins system influencing the
behaviour of epoxy hardeners in the epoxy resins system are: temperature of
the work area, temperature of the resin system (i.e. the heated resins) and
moisture. The structure of epoxy hardener is shown in Figure 1.4.
Figure 1.4 Structure of hardener
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1.6.2.2 Chemistry
The curing process is a chemical reaction in which the epoxide
groups in epoxy resin react with hardener to form a highly cross linked, three-
dimensional network. In order to convert epoxy resins into a hard, infusible
and rigid material, it is necessary to cure the resin with hardener. Epoxy resins
cure quickly and easily at any temperature from 5-150oC depending on the
choice of hardener. In the structure of unmodified epoxy prepolymer, ‘n’
represents the number of polymerized subunits and is in the range of 0 to 25.
When epoxy is mixed with the appropriate hardener, the resulting reaction is
exothermic and the oxygen on the epoxy monomers is flipped. This occurs
throughout the epoxy and a matrix with a high stress tolerance is formed that
glues the materials together (Figure s 1.4 and 1.5).
Figure 1.5 Chemical reaction between Bisphenol-A and Epichlorohydrin
1.7 BORASSUS FRUITS
The palm tree containing Borassus fruits are available all over the
world, especially abundantly in India. The palm tree is a native of tropical
Africa but cultivated and naturalized throughout India. The palm is a large
tree which may grow up to 30 m height and the trunk may have a
circumference of 1.7 m at the base. There may be 25-40 fresh leaves. Leaves
are leathery, grey green, fan-shaped, 1-3 m wide, folded along the midrib and
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are divided at the center. Their strong stalks, 1-1.2 m long, are edged with
hard spines.
The palm trees are usually grown well in the dry areas and are
drought resistant. The life of the trees will be more than 100 years. In India, it
is planted as a windbreak on the plains. It is also used as a natural shelter by
birds, bats and wild animals. The coconut-like fruits are three-sided when
young, becoming rounded or more or less oval, 12-15 cm wide and capped at
the base with overlapping sepals. When the fruit is very young, this flush is
hollow, soft as jelly and translucent like ice and is accompanied by a watery
liquid, sweetish and potable.
The Borassus fruit fiber is a cellulosic fiber. The cellulose is a long
chain polysaccharide made up of glucose monomer units, which are
alternately rotated to 180 degrees. Cellulose molecules align to form micro
fibrils of diameter of about 3–4 nm. The micro fibrils have both crystalline
and non-crystalline regions that merge together. The hemicelluloses, lignin
etc. bound the cellulose into fibril aggregates of diameter roughly 10–25 nm.
Hemicellulose binds to the surface of the cellulose micro fibrils, while lignin
cross-links the hemicellulose molecules of adjacent micro fibrils.
Hemicelluloses are short chain, amorphous polysaccharides with monomer
units with acidic groups. They include xyloglucans, xylans, glucomannans
and galactoglucomannans. Lignin is an amorphous, complex phenolic
compound.
Matured Borassus fruit contains cellulosic semi-solid flush which is
reinforced by the Borassus fruit fibers. The botanical name of Borassus fruit
fiber is Borassus flabellifer of family palmae (Figure 1.6).
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Figure 1.6 Palm tree containing Borassus fruits
1.8 SIGNIFICANCE OF NATURAL FIBER COMPOSITES
Natural fiber composites are emerging as promising replacements
for synthetic fiber polymer composites. Natural fibers offer both cost savings
and a reduction in density when compared to glass fibers. Though the strength
of natural fibers is not as great as glass, the specific properties are
comparable. These natural fiber composites demonstrate high strength and
high toughness and have been developed for a range of rigorous
environments. In addition, these composites can easily substitute conventional
materials in several areas such as the automotive industry, building industry,
consumer goods and sports goods. Many automotive and household
components are produced using natural composites, mainly based on
polyester and fiber like flax, hemp, pineapple, coir and sisal. The application
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of natural fiber composites in this industry is lead by motives of price and
weight reduction.
1.9 NEED FOR NATURAL FIBER COMPOSITES
Driven by increasing environmental awareness, automakers in the
1990s made significant advancements in the development of natural fiber
composites, with end-use primarily in automotive interiors. A number of
vehicle models, first in Europe and then in North America, featured natural
fiber-reinforced thermosets and thermoplastics in door panels, package trays,
seat backs and trunk liners. Promoted as low-cost and low-weight alternatives
to fiber glass, these agricultural products, including flax, jute, hemp and kenaf
induced the start of a "green" industry with enormous potential. There
remains, however, a general consensus about the main advantages of natural
fiber reinforcements, including lower weight, availability, ease of recycling,
thermal and acoustic insulation and carbon dioxide neutrality (when burned,
the natural fibers reportedly give off no more carbon dioxide (CO2) than they
consumed while growing). On an average, the production of natural fiber
suitable for composites is some 60 percent lower in energy consumption than
the manufacture of glass fibers. It is equally necessary to reduce
environmental impacts such as global warming, which are generated by
consumption of petroleum, a non renewable resource. The energy and
environmental comparisons of the natural fibers with the synthetic fibers are
the motivational factors promoting bio-fiber products.
1.10 SCOPE OF THE PRESENT WORK
The Borassus fruit fibers are inexpensive, naturally available,
renewable, eco-friendly and hence, the investigation of its potential properties
to the technical world is essential. An attempt is made in this research work to
study the properties of Borassus fruit fiber reinforcements in composites with
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and without alkali treatment and to introduce them as a natural reinforcement
to the composites. This work has the following objectives:
1. To safely extract Borassus fruit fibers from the fruits.
2. To find the best alkali treatment percentage required for the
fibers.
3. To study the physical, chemical and mechanical properties of
raw and alkali treated fibers.
4. To visualize the surface morphology of raw and alkali treated
fibers.
5. To study the chemical compounds of the fibers through
Fourier Transform Infrared Spectrometry analysis.
6. To make the chopped Borassus fruit fiber reinforced epoxy
composite specimens with different fiber lengths such as
1 mm, 3 mm, 5 mm, 7mm and 10 mm for both raw and alkali
treated Borassus fruit fibers.
7. To explore the mechanical properties such as (tensile strength,
compressive strength, impact strength, flexural strength,
machinability), Water absorption, Thermo gravimetric
analysis, Fourier Transform Infrared Spectrometry, Wear
analysis, Surface morphology using Scanning Electron
Microscope of both raw and alkali treated chopped Borassus
fruit fiber-epoxy composites with different fiber lengths.
8. To find the tribological properties of Borassus fruit fiber
reinforced composites and to visualize the surface morphology
of the worn surfaces.
9. To manufacture the application products by reinforcing the
alkali treated Borassus fruit fibers in epoxy.
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10. To introduce less weight, high strength, durable composites to
this technical world by Borassus fruit fiber-epoxy composites
through the above applications.
1.11 OUTLINE OF THE THESIS
Chapter 1 describes introduction about the Natural fibers and their
significance, types of Natural fibers, Benefits & Limitations of Natural fibers,
Polymer Matrix Materials, need for Natural fiber Composites, scope for the
Present work and Organization of thesis.
Chapter 2 describes the review of literature which discusses
Mechanical Properties of natural fibers, Mechanical Properties of Natural
fiber Composites, Tribological Behaviour of Natural fiber composites and
Applications.
Chapter 3 discussed about the Extraction of fiber, Alkali
Treatment, Physical, Chemical and Mechanical Test of Borassus fruit fiber,
preparation of Matrix and Mould, Tensile, Compressive, Impact, Flexural,
Water Absorption, Machinability, FTIR, SEM and TGA and Wear Tests.
Chapter 4 presents the Analysis of Borassus Fruit fiber, Analysis
of Borassus Fruit fiber Epoxy composites (Raw and Alkali treated), Wear
analysis of Borassus Fruit fiber Epoxy composites (Raw and Alkali treated)
and the results are discussed in detail.
Chapter 5 discusses the Application of Borassus Fruit fiber -
Epoxy Composites with the fabrication of Two wheeler Bumper, Tumbler
gear, Portable Gas Cylinder, Door Model and Solid Rod Model.
Chapter 6 Summarizes the thesis and provides suggestions for
future work.
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