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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.