A Study on Mechanical and Thermal Behavior

A Study on Mechanical and Thermal Behavior
A Study on Mechanical and Thermal Behavior
of Coir Fiber Reinforced Epoxy Composites
A thesis submitted in partial fulfilment of the
requirements for the degree of
Master of Technology
in
Mechanical Engineering
[Specialisation: Production engineering]
by
Binu Haridas
(Roll no: 212ME2287)
Department of Mechanical Engineering
National Institute of Technology
Rourkela, Orissa-769008
A Study on Mechanical and Thermal Behavior
of Coir Fiber Reinforced Epoxy Composites
A thesis submitted in partial fulfilment of the
requirements for the degree of
Master of Technology
in
Mechanical Engineering
[Specialisation: Production engineering]
by
Binu Haridas
(Roll no: 212ME2287)
Under the guidance
of
Prof. Sandhyarani Biswas
Department of Mechanical Engineering
National Institute of Technology
Rourkela, Orissa-769008
Department of Mechanical Engineering
National Institute of Technology
Rourkela, Orissa-769008
Certificate
This is to certify that the thesis entitled “A Study on Mechanical and Thermal Behavior of
Coir fiber Reinforced Epoxy Composites”, submitted to the National Institute of
Technology, Rourkela by Mr. Binu Haridas, Roll No: bearing Roll no. 212ME2287 in
partial fulfilment of the requirements for the award of Master of Technology in the
Department of Mechanical Engineering, National Institute of Technology, Rourkela, is
an authentic work carried out by him under my supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not been
submitted to any other university/institute for the award of any Degree or Diploma.
Prof. Sandhyarani Biswas
Place: Rourkela
Date:
Assistant Professor
Dept. of Mechanical Engineering
National Institute of Technology, Rourkela
i
Acknowledgement
With deep regards and profound respect, I avail this opportunity to express my deep sense of
gratitude and indebtedness to Prof. Sandhyarani Biswas, Department of Mechanical
Engineering, NIT Rourkela, for introducing the present research topic and for her inspiring
guidance, constructive criticism and valuable suggestion throughout this research work. It
would have not been possible for me to bring out this report without her help and constant
encouragement.
I express my sincere gratefulness to Prof. K. P. Maity, Head of the Department, Mechanical
Engineering, NIT Rourkela for giving me an opportunity to work on this project and allowing
me the access to valuable facilities in the department.
I am thankful to Mr. Vivek Mishra and Mr.Prabina Kumar Patnaik, Ph.D. scholars of
Mechanical Engineering Department for their support and help during my work. Last but not
the least I would like to thank Mr. Anurag Singh and Mr. Abhishek Kumar for their
motivation and support.
Binu Haridas
ii
Abstract
The main focus of this study is to utilize the properties of natural fibers and make
them compatible with polymer resins effectively. Coir fibres have been used as
reinforcement in epoxy resin with various weight percentages of 5%, 10% and 15%.
Surface treatment method like alkali treatment is done to improve the performance of
coir fibre on epoxy resin. Cow dung powder is added as filler to the composite with a
purpose of improving the insulation property of the composite. The mechanical
properties like tensile strength, flexural strength, impact strength and the micro
hardness showed an increment with respect to fibre loading as well as the alkali
treatment. The maximum value is found with the composite having 15% treated coir
fibre. Flexural strength showed maximum value at 10% treated fibre loading which
decreases after 10% fibre loading. When fibre loading was increased, thermal
conductivity reduces. By adding cow dung powder to the untreated fibre composite,
thermal conductivity is further decreased. From Thermo Gravimetric Analysis (TGA)
it is found that the surface treated fibre composites resist the thermal decomposition
effectively up to 2600C after that there is a considerable increase in the thermal
stability. Differential Scanning Calorimetry (DSC) showed that the specific heat
capacity increases with increase in fibre loading. Untreated fibre composites showed
better specific heat capacity than the treated ones. Cow dung powder added to the
untreated composite showed that maximum specific heat and specific heat capacity
increases further to higher values as the quantity of cow dung powder is increased.
Glass transition temperature (Tg) showed an increment with surface treatment as
well as fibre loading of up to 10% and after that it decreases.
Keywords: alkali treatment, coir fibre, composite, glass transition temperature,
specific heat capacity, thermal conductivity.
iii
Contents
Acknowledgement…………………………………………………………………….
ii
Abstract………………………………………………………………………………..
iii
List of tables…………………………………………………………………………..
vi
List of figures………………………………………………………………………….
vii
Chapter 1 Introduction…………………………………………………………........
1
1.1 Motivation and background………………………………..........
1
1.2 Classification of Composites…………………………………….
2
1.3Types of Polymer Resins………………………………………...
5
1.4Types of Fibers …………………………………………………
5
1.5Basic Structure of Natural Fibers ………………………………..
6
1.6 Coir Fiber………………………………………………………..
8
1.7 Thesis Outline…………………………………………………...
8
Chapter 2 Literature review…………………………………………………………
9
2.1 About the Mechanical Properties of Natural Fiber Based Polymer
Composite……………………………………………...
9
2.2 On the Thermal Physical Properties of Natural Fiber Based
Polymer Composite……………………………………………...
12
2.3 On the Thermal Stability of Natural Fiber Based Polymer
Composite……………………………………………………….
2.4 Objective of the present work…………………………………...
14
15
Chapter 3 Materials and methods……………………………………………………
16
3.1 Materials…………………………………………………………
16
3.2 Alkali treatment …………………………………………………
16
3.3Composite fabrication…………………………............................
17
3.4 Mechanical Property Tests…………………………………………
18
3.4.1 Tensile Strength…………………………………………
18
3.4.2 Flexural strength………………………………………...
18
3.4.3 Micro-hardness………………………………………….
19
3.4.4 Impact Test………………………………………….......
20
3.5Optical Microscope…………………………………………………
21
3.6 Thermal Property Testing………………………………………….
22
iv
Chapter4
3.6.1 Thermal Conductivity Testing…………………….......
22
3.6.2 Thermo gravimetric Analysis……………………….......
23
3.6.3 Differential Scanning Calorimeter………………….......
24
Results and discussions……………………………………………………..
25
4.1 Mechanical Characteristics of Composites…………………….......
25
4.1.1 Effect of fibre and filler concentration on hardness of
composites……………………………………………….
4.1.2 Effect of fibre and filler concentration on tensile
strength of the composites……………………………....
4.1.3 Effect of fibre and filler concentration on flexural
strength of composites………………………………...
4.1.4 Effect of fibre and filler concentration on impact
strength of composites…………………………………..
4.2 Optical microscopic images………………………………………..
Chapter5
25
26
28
29
31
4.3 Thermal Characteristics of Composites……………………………
32
4.3.1 Effect of fibre concentration and the addition of cow
dung powder on Transverse Thermal Conductivity of
composite……………………………………………….
4.3.2 Thermo gravimetric Analysis…………………………...
32
34
4.3.3 Effect of fibre concentration and the addition of cow
dung powder on Specific Heat Capacity of composite…
4.3.4 Effect of fiber concentration on Glass Transition
temperature of composite……………………………….
Conclusion………………………………………………………………….
5.1 Scope of future work……………………………………………...
Reference……………………………………………………………………
v
34
36
39
40
41
List of Tables
Table.
No
Table description
Page
No
Table 1.1
Physical properties of natural fibers
6
Table 3.1
Designation of Composites
17
vi
List of Figures
Figure description
Fig.
No.
Page.
No
Fig. 1.1
Schematic diagram of classification of composite according to the type
of reinforcement used
2
Fig. 1.2
Types of FRPs a) discontinuous fibers (unidirectional) b)
discontinuous fibers (random) c) continuous fibers (unidirectional)
3
Fig. 1.3
Classification of composites
4
Fig. 1.4
Structure of natural fiber
7
Fig. 3.1
Loading arrangement for tensile test
18
Fig. 3.2
Loading arrangement for three point bending test
19
Fig. 3.3
Experimental set up for Micro-hardness test
20
Fig. 3.4
Pictorial view of Impact tester
21
Fig. 3.5
Schematic diagram of an optical microscope
21
Fig. 3.6
Schematic arrangement of guarded heat flow meter
22
Fig. 3.7
Schematic arrangement of TGA set up
23
Fig. 3.8
Schematic arrangement of DSC
24
Fig. 4.1
Variation of Hardness of composite with respect to fiber loading
25
Fig. 4.2
Effect of Cow dung powder on Hardness of Composite
26
Fig. 4.3
Variation on Tensile Strength of composite with respect to fiber
loading
27
vii
Fig. 4.4
Effect of Cow dung powder on Tensile Strength of Composite
27
Fig. 4.5
Variation on flexural strength of composites with respect to fiber
loading
28
Fig. 4.6
Effect of Cow dung powder on Flexural Strength of Composite
29
Fig. 4.7
Variation of impact strength of composites with respect to fiber
loading
30
Fig. 4.8
Effect of Cow dung powder on Impact Strength of Composite
30
Fig. 4.9
Optical Microscopic images of composites
31
Fig. 4.10
Significance of fiber loading on thermal conductivity of composite
32
Fig. 4.11
Variation of thermal conductivity of composite with respect to the
addition of cow dung powder
33
Fig. 4.12
Comparison on thermal stability of alkali treated and untreated fiber
filled composites
34
Fig. 4.13
Variation of specific heat capacity of composite with respect to fiber
35
concentration
Fig. 4.14
Effect of cow dung on Specific Heat Capacity of composite
36
Fig. 4.15
Effect of fiber concentration on Glass Transition Temperature of
37
Composite.
Fig. 4.16
Effect of cow dung on Glass Transition Temperature of composite
viii
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CHAPTER 1
INTRODUCTION
1.1Motivation and background
Composite materials are being widely used in recent period for day to day applications and at the
same time they possess a vital role in manufacturing of highly sophisticated machines and
equipment also. Composite materials has many advantages over the conventional materials such
as light weight, simple and cheap manufacturing process and also have comparable properties of
their constituent materials [1]. So the main task for researchers are to improve the properties of
composite materials according to the application and make them more durable, weightless and
cost effective.
Composites consists of two phases one is called discrete phase called reinforcing material, which
may be fiber, particulate or flakes and the other is a continuous phase which termed as matrix
material which possess the major share of composite material. In a composite material
components like matrix and fibers are bounded together but its main difference from an alloy is
that its constituents will retain their own identity and properties [2]. If we define composite
materials, it is a unique combination of fiber and matrix where function of the fiber is to
withstand load and make the composite stiffer meanwhile matrix is a binder which holds the
fiber in place [3].
Composite shows advantages like low weight, low density, low cost and good specific properties
like tensile, flexural and impact strengths. It may possess applications in area where weight of
the total equipment is a major problem, like rocket technology, aircraft industry, marine
structures etc. By combining with some insulating material, composites can also utilized as
thermal and electrical insulating material. Composites are used to prepare many mechanical
components like brakes, drive shafts, flywheels, pressure vessels etc [4].
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1.2 Classification of Composites
According to the reinforcing phases the composites are mainly classified into three types, i.e.
fiber reinforced composites, flake reinforced composites and particle reinforced composites [5].
The schematic diagram of classification of composite according to the type of reinforcement
used is shown in figure 1.1. Fiber reinforced composites consists of fiber and matrix, former
provides strength while latter glues all the fiber together and transfers stress between the
reinforcing fibers. The primary function of fiber is to carry the loads in the longitudinal direction.
Glass fiber, polyester fibers, coir, jute etc. are some example of the fibers which are used as the
reinforcing material. In Flake Reinforced Composites material flakes are used as reinforcing
material. The flakes will be more or less oriented in a plane so such composites often have the
behavior of biaxial oriented material. Flake composites have strong resistance against puncturing
by sharp objects. They have high moduli and high aspect ratio compared to the particulate and
fiber reinforced composites. Examples are mica, graphite, glass flakes, aluminum flakes etc. The
flakes composites are discontinuously reinforced polymer composites which exhibits improved
mechanical properties and possess relative easiness in fabrication and manufacturing [6].
Particles of various sizes are randomly distributes in particulate reinforced composites. Examples
are aluminum particles, Cu particles etc.
Figure.1.1: Schematic diagram of classification of composite according to the type of
reinforcement used [5].
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Fiber-reinforced polymer (FRP) composites are fabricated by combining polymer resin with
strong reinforcing fibers. The components maintains its original properties and contribute their
own individual properties to the new composite material so that the overall property will be
enhanced. The polymer resins are typically viscous, and may be easily molded, but are
comparatively weak to fibers. The resin component acts as a binder in between the reinforcing
fibers and also acts as a medium to transfer stress. The FRP shows low specific gravity, low
strength weight ratio and low modulus weight ratio makes them superior to metallic materials.
Over a long period of time, the high-strength and light weight FRP composites materials have
been used largely in defense and aerospace systems [7]. Recently, it has been applied for
preparing luxury items like table, chairs and doors etc. as a substitution to metals and alloys.
They are also used in automobile and aerospace sectors to reduce the weight of the components
which results in substantial saving of the fuel and energy during transportation.
Figure.1.2: Types of FRPs
a) discontinuous fibers (unidirectional) b) discontinuous fibers
(random) c) continuous fibers (unidirectional) [8]
According to the type of matrix material used, composites can be categorized as Polymer Matrix
Composites (PMC), Metal Matrix Composites (MMC), and Ceramic Matrix Composites (CMC).
MMC consists of at least two components one is a metallic part which functions as matrix and
other part may be ceramic or organic material. MMC have many advantageous over monolithic
metals such that they possess higher specific strength, high specific modulus, low thermal
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coefficient of expansion and excellent wear resistance. But the toughness of MMC is lower than
metals [9]. CMC consists of fiber embedded in ceramic matrix. They are not widely being
established in service like PMCs because the processing temperature of CMCs are very high. In
PMC, the matrix is a polymer which may be thermoplastic or thermosets and is reinforced by
fiber or fillers. Compared to MMC and CMC, PMC are widely used because of the relative
easiness to produce them and also due to its light weight and low cost. They possess application
in aircraft, space shuttle, rocket, rotor blades etc. There are several criteria, on which composite
material can be classified, like on the basis of type of matrix material used, type of reinforcement
used, type of fibers used. Figure 1.3 shows the classification of composite material on the basis
of physical structure and geometry.
Figure.1.3: Classification of composites [3]
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1.3 Types of Polymer Resins
In general, polymers are classified as thermoplastics and thermosets. Thermoplastics are linear
polymers which acquires new shapes on the application of heat and pressure. Examples are
nylons, polystyrene, polyethylene, PVC, polypropylene etc. Thermosets are cross-linked
polymers, this crosslinks pulls each parallel chains and brings a strong bond. They can’t be
reshaped by heating because of this crosslinks [10]. Thermoset polymers are used at high
temperatures and also have better creep property than thermoplastics. Examples are epoxy,
polyester, phenolic, bakelite, polyurethanes etc.
Epoxy resins is one of the widely used thermosetting polymer. Commercially it is known as
araldite or epon. It is formed by polycondensation reaction of epichlorohydrin and bisphenol-A.
Epoxies are stiffer, stronger and shows effective thermal and electrical insulation properties,
chemically resistant and low toxic also. They are available in abroad range of physical forms,
from low viscous liquids to high viscous solids. . Epoxy resin composites are used largely in
industry because of its high toughness, adhesiveness and chemical resistant nature.
1.4) Types of Fibers
In general, fibers are categorized into two groups i.e. natural and synthetic fibers. Glass fibers,
carbon fibers, CNT are some examples of synthetic fibers. Synthetic fiber possess high elastic
modulus, strength and resilience and they are hydrophobic in nature also. But, these days natural
fibers receives a lot of attention due to its low cost, comparable strength to synthetic fibers, low
density, non-toxicity and biodegradability. Depending upon the source of availability, natural
fibers are divided by categories: seed hair, bast fibers, and leaf fibers. Some examples are cotton
(seed hairs); ramie, jute, and flax (bast fibers); and sisal and abaca (leaf fibers). Among these
fibers jute, ramie, coir, flax, sisal, hemp etc, are the most generally using fibers for fabrication of
polymer matrix composites. Table 1.1 shows the physical properties of these natural fibers.
Sometimes natural fibers in the form of wood-flakes have also been used for fabrication of
composites. One of the main drawback of natural fibers are their hydrophilic behavior. So they
have the tendency to absorb the moisture from atmosphere and it causes dimensional and
property changes. The other major challenge in the application of natural fibers are their poor
compatibility with polymer so that the stress transfer is not so acceptable. To improve the
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compatibility with matrix natural fiber can be subjected to various surface modification treatment
like alkali treatment, acetylation, cyanoethylation, bleaching etc.
Table .1.1: Physical properties of natural fibers [11]
Properties
Unit
Coir
Flax
Hemp
Jute
Ramie
Sisal
Density
g/m3
1.25-1.5
1.4
1.48
1.45
1.5
1.26-1.33
Diameter
m
100-450
100
25
60
40-50
100-300
%
36-43
62-72
67-75
59-71
68-76
60-67
%
0.2
16-18
16-18
12-13
13-14
10-13.9
%
41-45
2-2.5
2.8-3.3
11.8-12.9
0.6-0.7
deg
30-45
10
6.2
7-9
7.5-12
10-20
Mpa
105-175
800-1500
550-900
400-800
500-870
600-700
Gpa
4-6
60-80
70
10-30
44
38
%
17-47
1.2-2.4
1.6
1.16-1.8
1.2
3.64-5.12
%
10
7
8
12
12-17
11
Cellulose
content
Hemicellulose
Content
Lignin
Content
Microfibrillar
angle
Tensile
Strength
Young’s
Modulus
Elongation at
break
Moisture
Absorption
8-12
1.5) Basic Structure of Natural Fibers
If we examine the structure of natural fiber, they are mainly consists of five components i.e.
cellulose microfibriles, hemicellulose, lignin, pectin and waxes. Cellulose is a type of natural
polymer which is formed by repeating units of D-anhydroglucose and the units are joined by β-1,
4-glycosidic linkages. Hemicellulose consists of a group of polysaccharides which combined to
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form 5 and 6 –carbon ring sugars. Lignin is total insoluble component and hydrophobic in nature
among this group and is basically a complex hydrocarbon polymer consists of both aliphatic and
aromatic group. A group of heteropolysaccharides which are collectively called as pectin. Waxes
are also the component of natural fiber that consists of various types of alcohol.
Basically natural fibers are multilayered structures consists of primary layer and secondary layers
as shown like figure 1.4. Here primary layer which forms at the time of cell growth and which
surrounds the secondary layers. Each layer consists of thick walls and are called primary wall
and secondary walls. The middle layer of secondary wall is the thickest among secondary walls
and that determines mechanical property of fiber.
The main content of natural fiber is cellulose
micro fibrils which are bonded by amorphous materials called hemicellulose. The angle between
micro fibrils orientation in the structure and the axis of main fiber body is called microfibrilar
angle. The microfibrilar angle is different for different natural fibers and that determines the
mechanical strength of fibers. The interesting thing is that the natural fibers itself act as a
composite material where amorphous materials like hemicellulose, pectin and wax acts as a
matrix which bonds the microfibrilar cellulose. The hemicellulose molecules are making
hydrogen bond to microfibrilar cellulose and functions as a binding material. Lignin acts as a
coupling agent which helps to improve the stiffness of the cellulose/hemicellulose composite
[12].
Figure.1.4: Structure of natural fiber [13]
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1.6) Coir Fiber
Coir fiber is extensively for preparing ropes, yarns, mattresses, mats, sacking, brushes, caulking
boats, insulation panels and floor tiles [14]. It is a lignocellulostic fiber which extracts from the
seed of coconut palm. Coir has low tensile strength and young’s modulus because of its low
cellulose and high lignin contents. Coir has high microfibrilar angle due to which it possess low
moduli. But the percentage of elongation of break and toughness of coir fiber is higher than other
natural fibers. It also exhibits much better resistance to weather, fungal and bacterial because of
its high lignin content [11]. The incorporation of coir as a component in polymer composites is
unsatisfactory in some perspective compared to other natural fiber because of its low cellulose
content (36–43%), high lignin content (41–45%) and high microfibrilar angle. Morphological
investigations carried out by the researchers on coir fibers reveals that the external sheath of
lignin obstructs the cellulose to make interfacial bond with the polymers. The removal of this
peripheral layer of lignin generally brings about a superior and more stable interfacial bond. To
attain this, there are several treatments that are widely established such as alkali treatment,
bleaching and graft copolymerization etc, by which the surface properties of natural fibers can be
enhanced. The coir industry is much developed in India, Srilanka and Brazil. The coir fiber
polymer has many application in structural systems in housing, electrical panels, ducting etc. The
other main feature of coir fibers are its low thermal and electrical conductivity. Thus, the coir
composites can be used as low temperature insulating materials in household application and
electronic packaging.
1.7) Thesis Outline
The remainder of this thesis is organized as follows:
Chapter 2: This includes the information of previous research work that gives support and
backup to the present work that is being described here.
Chapter 3: Includes the detail description of materials required, processing techniques and theory
behind the experiment for characterization of the composites under investigation.
Chapter 4: This chapter presents the results and discussion of the mechanical and thermal tests of
the coir-epoxy and cow dung filled hybrid composites.
Chapter 5: This chapter presents the conclusions and recommendations for the corrections and
modification to be implemented for future work.
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CHAPTER 2
LITERATURE REVIEW
This chapter deals with the supporting knowledge that had developed in past for using enough
data for the present work. A thorough review of the available literates was also done to
understand the effect of various parameters that influence the mechanical and thermal properties
of fiber reinforced polymer composites. The literature survey is done on the basis of following
points:
2.1) About the Mechanical Properties of Natural Fiber Based Polymer Composite
The growing factors like environmental challenges, biodegradability, non-toxicity etc, leads the
researchers to focus their studies on exploring the features of natural materials like natural fibers.
A lot of research is going on to make use of natural fibers as a reinforcing material in the
polymer matrix composites. There are a lot of challenges faced by the researchers to make the
natural fiber suitable for their needs due to its hydrophilic nature, thermal and chemical
instability. But now a days natural fibers can replace synthetic fibers to some extent by making
them compatible with polymer matrixes by some surface modification techniques.
Rout et al. [15] studied the significance of surface treatment on the coir reinforced polyester
composites. The coir fiber was subjected to alkali treatment, vinyl grafting, and bleaching before
adding them with general purpose polyester resin. The mechanical charecteristics like tensile
strength, bending and impact strength were increased because of surface treatment. Bleached
fiber composite (at 650C) showed better flexural strength. NaOH treated fiber/polyester
composite exhibited better tensile strength. Because of the chemical treatments of fibers the
water absorption tendency of composite was reduced Biswas et al. [16] carried out a study on the
significance of fiber length on the mechanical charecter of coir/epoxy composite. It was found
that the hardness of the composite decreases by increasing length of fiber up to 20 mm and then
after it increases. They also concluded that fiber length has a major influence on enhancing
mechanical properties like tensile strength, flexural strength and impact strength. Romli et al.
[17] done a factorial study upon tensile strength of coir reinforced epoxy composite. In their
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study, the volume fraction, curing time and compression load during the solidification of
composites were taken as parameters. From the results, they concluded that volume fraction
influences the tensile strength of the composites. Authors also increased the percentage volume
fraction of fiber and found that the tensile properties of composites increased to some extent.
Curing time also showed some effects on the characteristics of composites meanwhile the
influence of compression load on the properties of composites were not revealed properly.
Lu et al. [18] worked on bamboo/epoxy composites and the mechanical charecter of composites
were compared. Samples with different volume fraction were prepared using treated fiber.
Surface modification of fibers was done using NaOH and silane coupling agent (KH560). FTIR
analysis was also performed to observe the chemical structure of the fibers. From the analysis
they concluded that NaOH would partially dissolve the lignin and hemicellulose from the
periphery of fiber and created some porosity on the surface of fiber. It would increase the
interlocking capacity of fiber and eventually fiber would be adhered to matrix firmly. The silane
treatment of the fibers leads to the formation of Si-O-Si and Si-O-C chemical bonds with the
cellulose surfaces which results in enhanced mechanical properties of the composites. They
concluded that the tensile strength of the composites was much higher in silane treated fibers
than alkali treated.
Nam et al. [11] studied the significance of alkali treatment on interfacial bonding and mechanical
properties of coir fiber filled poly (butylene succinate) biodegradable composites. Composites
with fiber concentration of 10-30 % were prepared using 5 % NaOH treated fibers. On
comparing with untreated fiber composites authors found a remarkable improvement in the
interfacial shear strength (IFSS) and mechanical properties of treated coir fiber/ polybutylene
succinate (PBS) composites. The treated composites with 25 % fiber content exhibits higher
mechanical properties. Samal et al. [19] prepared bamboo as well as glass fiber filled
polypropylene hybrid composites and examined their mechanical, thermal and morphological
properties. They also added maleic anhydride grafted polypropylene (MAPP) to the composite in
order to enhance the interfacial bonding between the fibers and matrix. It was reported that the
hybrid composite shows improved mechanical properties like tensile, impact and flexural
strength as compared with virgin polypropylene. SEM micrograph of the composites showed a
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reduction in the interfacial gap between fiber and matrix. TGA showed the improved thermal
stability of hybrid composite compared to the polymer.
Mishra and Biswas [20] fabricated jute fiber epoxy composites by hand lay-up method and
studied the physical and mechanical properties of the prepared composites. They concluded that
the presence of voids in the composites adversely affect its mechanical properties.
Mir et al. [21] performed surface treatment on coir fiber, after that a systematic investigation on
the mechanical and physical properties of coir-polypropylene bio composites had conducted. For
improving the compatibility with polypropylene matrix, the coir fiber was reacted with basic
chromium sulfate and sodium bicarbonate salt in acidic solution. Composites with fiber
percentage of 10, 15 and 20 were prepared. The study reveals that the chemically treated fiber
based composite showed good mechanical charecters than untreated. The composite with 20%
fiber weight concentration exhibited optimum mechanical property compared to other. During
surface treatment, the OH groups of untreated coir cellulose which were hydrophilic in nature
had been changed to hydrophobic –OH-Cr groups. Because of this, the water absorption amount
of composite was also lowered. Reddy et al. [22] treated glass/bamboo hybrid fiber reinforced
polyester composites with some chemicals such as sodium carbonates, sodium hydroxide, acetic
acid, benzene, carbon tetrachloride, ammonium hydroxide, toluene and water to check the
chemical resistivity of the composite. It was observed that the hybrid composites showed
excellent resistance to chemicals and the tensile strength of alkali treated hybrid composite was
also improved. The reason found that once the fiber subjected to alkali treatment, the amorphous
hemicellulose can be removed to certain extent and eventually composite may show some
crystalline behavior.
Sreenivasan et al. [23] compared the mechanical properties of untreated and surface treated
Sansevieria cylindrica fibers (SCFs) /polyester composites. Surface treatments such as alkali,
potassium permanganate, benzoyl peroxide and stearic acid were performed in order to modify
the fiber surface. They concluded that the surface treated fiber showed improved mechanical
property than the untreated fiber. Composites with potassium permanganate treated fiber
exhibited better mechanical property due to better compatibility of fiber upon matrix. Monteiro
et al. [24] conducted a study on the mechanical characteristics of coir fiber reinforced polyester
composites. The coir fiber percentage was increased up to 80 % and found that up to 50% fiber
loading, composites were become rigid, and after that composites behaves like agglomerates. A
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systematic study on the influence of lignin as a compatibilizer on the physical property of coir
fiber reinforced polypropylene composites were performed by Rozman et al. [25]. They made
the conclusion that the coir fiber filled polypropylene composites with lignin as a compatibilizer
was performed better flexural properties than control composites. Tensile properties were not at
all improved where lignin was incorporated as a compatibilizer.
The use of coir fibre reinforced polypropylene composite for the panel of automotive interior
applications was studied by Ayrilmis et al. [26]. This study proved that the coir fibre would be a
vital component in the production of thermoplastic composites, especially for the effective
replacement of comparatively highly expensive and dense glass fibres. When the coir fiber
quantity increased up to 60 wt %, the flexural and tensile properties of the composites improved
by 26% and 35%, respectively. Even if the further increase in fibre quantity caused to decreases
the flexural and tensile properties because of the inadequate coverage of all the surfaces of the
coir fibre in polymer matrix. Pothan et al. [27] studied the significance of fiber length and fiber
quantity on short banana fiber filled polyester composite. The maximum tensile strength was
obtained at a fiber length of
30 mm and impact strength was getting maximum at of 40 mm
fiber length banana fiber polyester composite. As the fiber quantity increased up to 40%, the
tensile strength increased by 20% and there was a 34% increase in impact strength also.
2.2) On the Thermal Physical Properties of Natural Fiber Based Polymer Composite
Ramanaiah et al [28] studied mechanical, thermo physical and fire features of polyester
composites reinforced with sansevieria fibre. It was observed that at maximum fiber content, the
tensile and mechanical properties were increasing 2.55 and 4.2 times to that of neat resin
respectively. The thermal conductivity was measured by heat flow meter and found that the
thermal conductivity was decreasing with the volume fraction of fiber. But they found that the
thermal conductivity was increasing with the increase of temperature. Specific heat capacity of
composite was also observed and found that that was also increasing with the temperature.
Weidenfeller et al. [29] justified the interconnectivity significance of the filler particles in
between the fiber and matrix upon thermal conductivity. They observed a remarkable
improvement in the thermal conductivity of the polypropylene matrix from 0.27 up to 2.5W/m-K
with the addition of 30 vol% talc. The interesting fact was that, while adding the same volume
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quantity of copper particles caused a thermal conductivity raised to 1.25 W/m-K even if copper
particles have a thermal conductivity almost 40 times that of talc particles. This is because of the
strong interfacial bond between talc and fiber compared to copper and fiber.
Reddy et al [30] studied the thermal conductivity of characteristics of cow dung powder filled
glass/polyester hybrid composite. It was found that as the volume fraction of cow dung powder
increased, the thermal conductivity of the composite was decreased.Ramanaiah et al [31] studied
on the mechanical and thermal properties of polyester composites reinforced with waste grass
broom fiber. They varied the volume fraction of fibers in the composites from 0.163 to 0.358.It
was observed that the thermal conductivity of the composite decreased gradually as the volume
fraction of fiber increased. And a quite opposite result of increase of thermal conductivity was
found when the temperature increased. Specific heat capacity had also measured and found a
similar tendency of that thermal conductivity. Volume fraction and temperature had no influence
on thermal diffusivity. Fernandez et al [32] made cork polyethylene composite and studied its
characteristics. Its thermal and acoustic properties, impact strength, hardness, dimensional
stability were tested. The obtained results showed that this natural-based composite exhibits
improved characteristics such as low water absorption, impact resistance, fire resistance, and
insulation properties than conventional materials.
Kalaprasad et al. [33] studied thermal conductivity and thermal diffusivity studies of sisal, glass
and intimately mixed sisal/glass fiber reinforced low-density polyethylene composites. It was
observed that sisal reinforced polyethylene composite and the low density polyethylene shows
almost same variation of thermal conductivity with temperature. Here the rate of thermal
conductivity increased in glass fiber .polyethylene composite was higher than sisal /polyethylene
composite. The thermal conductivity of glass fiber showed higher because of the existence of
Fe2+metal ions content in E-glass fibre. Kumlutas and Tavman [34] conducted a numerical and
experimental study on thermal conductivity of particle reinforced polymer composites, they
observed that if tin particle was filled HDPE in a volume ratio of 8% and 16% they observed that
the thermal conductivity raises from 0.554W/m/K to 0.681W/m/K and 1.168W/m/K
respectively.
Idicula et al [35] carried out the experiment on the thermo physical characteristics of polyester
composites reinforced with natural fibre. Thermal conductivity, thermal diffusivity, and specific
heat of banana/sisal /polyester hybrid composer was evaluvated.They concluded that with the
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incorporation of the banana/sisal fiber the effective thermal conductivity of the composite
reduces. They also fabricated PALF/Glass reinforced hybrid polyester composite and found that
the thermal conductivity was increased with addition of glass fibers. The sisal and banana fiber
undergone chemical treatment such as NaOH and PSMA and obtained a much better
conductivity compared to untreated fiber composites.
2.3) On the Thermal Stability of Natural Fiber Based Polymer Composite
Shekeil et al. [36] studied the mechanical, morphological and thermal characteristics of poly
(vinyl chloride)/thermoplastic polyurethane poly-blend composites reinforced with kenaf fibers
on the basis of increasing fiber content. The mechanical properties like tensile strength, flexural
strength were improved with the increase in fiber content. For observing the thermal stability,
thermo gravimetric analysis carried out. They concluded that the thermal degradation takes place
in three stages. In the first stage, composites as well as the matrix had a similar stability. Matrix
showed a slightly improved stability than the composites at the second stage. And at the final
stage, composites showed a greater stability compared to the matrix. Rosa et al. [37] studied the
significance of fiber surface treatments on mechanical and thermal characteristics of
starch/ethylene vinyl alcohol copolymers reinforced coir composites. All experiments leads to an
enhanced the thermal stability of the fibers and finally to the composites. The better stability
attained to the composite which contain mercerized coir fiber. In addition to this, the mechanical
properties like tensile and flexural strength also increases with the effect of mercerization. Azwa
and Yousif [38] fabricated kenaf/epoxy composite and characterized it thermal decomposition
property at high temperature. Weight loss and physical changes were also observed by furnace
pyrolysis method. The results from the TGA exhibited that when kenaf fibres volume fraction
increased into the epoxy, both thermal stability and charring of the composites increases. Even if,
it was detected that after alkalization, there would be a decrease in these performances for the
kenaf/epoxy composite. Kumar et al. [39] made composite with coconut sheath fiber and epoxy
resin then compared the mechanical properties and thermal degradation phenomena with its
treated category. They found a sound increase in mechanical property in treated coconut sheath
fiber epoxy fiber than untreated category.TGA had also conducted and observed that the treated
composite had showed better thermal stability and less char yield than untreated composites.
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2.4) Objective of the present Work
From inspiration of the research work that had conducted already, the following points, which
outlined below are the highlights of present study
 To functionalize the coir fiber with the treatment of NaOH and fabricate epoxy composite
filled with both treated and untreated coir fiber by hand lay-up method.
 To study the mechanical charecteristics like tensile strength, flexural strength, impact
strength and hardness of treated fiber composite, untreated fiber composites and cow
dung powder filled untreated composites.
 To study the thermo physical properties like thermal conductivity, specific heat capacity
of both the treated and untreated fiber reinforced composites.
 To estimate the thermal conductivity of cow dung powder filled coir/epoxy composite.
 To study the importance of fiber surface treatment on thermal stability of composites.
 To study the surface morphology of composites using optical microscope.
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CHAPTER 3
MATERIALS AND METHODS
This chapter contains the details about materials and the experimental procedure that were
considered for the fabrication of composite and the test procedure followed for testing the
characterization of composites, respectively. The raw materials used for fabrication are
1. Coir fiber
2. Epoxy
3. Hardener
3.1) Materials
The coir fiber used for the preparation of composites are arranged from local resources. First of
all the coir fibers are segregated finely and they cut into pieces of length about 12 mm. The
Epoxy resin(LY 556) is taken as matrix binder is distributed by Ciba Geigy India Ltd.
Commonly epoxy resin have poor mechanical and thermal properties. For getting the properties
to be improved, the resin should undergo curing reaction in which the liner epoxy resin structure
changes to form three-dimensional cross-linked thermoset structure. This curing reaction takes
place by adding a curing agent called hardener in a ratio of 10:1 to epoxy resin. The following
reaction is an exothermic reaction in which homopolymerisation of resin takes place. The curing
agent or hardener is triethylenetetramine (HY-951) is also supplied from Ciba Geigy India Ltd.
3.2) Alkali treatment
In order to get improved mechanical and physical characters of the composites, coir fiber is
subjected to alkali treatment process. In alkali treatment, fibers are firstly prewashed with huge
amount of distilled water and dried at constant temperature of 50 0C. The alkalization process
consisted of immersing coir fibers of certain weight in a 5% (w/v) NaOH aqueous solution for 3
h at 700C. After that, fiber is removed from alkali solution and is dipped in 5 % acetic acid
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solution for neutralizing. Then it is washed with plenty of distilled water and is dried in an
electric oven at a temperature of 1100C for 2hr [37].
3.3) Composite fabrication
Fabrication of composite is done by conventional method called hand lay-up method. A mold of
dimension 210 × 210 × 40 mm3 is used. Epoxy resin with its corresponding hardener in a ratio
of 10:1 is thoroughly mixed. Mold releasing silicon spray is applied to mold releasing sheet and
then the chopped fiber, mixed with the resin is gently poured on the sheet which is placed inside
the mold. The purpose of releasing agent is to facilitate easy removal of the composite from the
mold after curing. The mixture is allow to set inside the mold for a period of 24 hr under a
pressure of 20kg over the cast. Then the specimen is cut into appropriate dimension for
mechanical and thermal tests. In this fabrication procedure ,three classes of composites are made
with different compositions are shown in the table no:3.1.Cow dung powder is added in one
group of composite in a weight percentage of 5%, 10% and 15% for improving the thermal
properties of composites.
Table.3.1: Designation of Composites
Composites
Epoxy
Coir –
Coir -treated
untreated
(wt %)
(wt %)
Cow
dung
(wt %)
powder
(wt %)
C1
100
0
0
0
C2
95
5
0
0
C3
90
10
0
0
C4
85
15
0
0
C5
80
15
0
5
C6
75
15
0
10
C7
70
15
0
15
C8
95
0
5
0
C9
90
0
10
0
C10
85
0
15
0
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3.4) Mechanical Property Tests
3.4.1) Tensile Strength
The tensile test of the composites were performed as per the ASTM D3039 standards. The test
was done using a universal testing machine (Tinius Olsen H10KS).The specimen of required
dimension 100 x 15 x 6 mm3 dimension was cut from the composite cast. The test was conducted
at a constant strain rate of 2 mm/min. The tensile test arrangement is shown in figure 3.1
Figure.3.1: Loading arrangement for tensile test
3.4.2) Flexural strength
The flexural strength of a composite is the maximum tensile stress that it can withstand during
bending before reaching the breaking point. The flexural test of the composites were performed
as per ASTM D790-03 test standards. The three point bend test was performed on the composites
using same universal testing machine (Tinius Olsen H10KS) at a cross head speed of 1mm/min.
The loading arrangement for the flexural test is shown in Figure 3.2. The test was repeated three
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times for each composite type and the mean value was taken. The flexural strength is determined
as
f=3PL/2bt2
(3.1)
Where, L is the span length of the sample (mm)
P is maximum load (N)
b the width of specimen (mm)
t the thickness of specimen (mm)
Figure.3.2: Loading arrangement for three point bending test
3.4.3) Micro-hardness
Leitz micro-hardness tester was used to measure the micro-hardness of composite specimens.
Figure 3.3 shows the experimental set up for the micro-hardness test. A diamond intender with
an apical angle of 136° was intended over the surface of the specimen under a load of 2.94 N.
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After the removal of load the two diagonals D1 and D2 of the indentation were measured. The
hardness value was calculated using the Equation (3.3)
Hv=0.1889F/L2
(3.2)
L= (D1 +D2 )/2
(3.3)
where, F is the applied load (N), L is the diagonal of square impression (mm), D1 is the
horizontal length (mm) and D2is the vertical length (mm).
Figure.3.3: Experimental set up for Micro-hardness test
3.4.4) Impact Test
Impact tests were performed to understand the toughness of material. During the test, specimens
were subjected to a large amount of force for a very short interval of time. For any material, the
higher amount of impact strength indicates that it can absorb a large amount of energy before
failure. As the impact energy increases the toughness of material increases and its plasticity will
be also large. The pictorial view of impact tester is shown in figure 3.4. The specimen was
clamped into the tester and the pendulum was released from a height to strike the specimen. The
corresponding values of impact energy of different specimens were getting directly from the dial
indicator. The size of the specimen for the impact test was 64 x 12.7 x 3.2 mm3.
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Figure.3.4: Pictorial view of Impact tester.
3.5) Optical Microscope
The optical microscope, often considered as the light microscope, is a type of microscope which
uses light and magnify images of small samples with the help of lenses. A diagram of typical
arrangement of optical microscope is shown in figure 3.5. Generally, they are classified as
simple microscope and compound microscope. A simple microscope is a microscope that
provides angular magnification with the help of single or a group of lenses. Simple microscopes
are not capable of high magnification. A compound microscope is a microscope which has two
types of lenses. One close to the object to gather the light from object called objective lenses and
other close to eye called eye piece. The compound microscope gives better magnification than
simple microscope. Here the microscope of model used for magnifying the image of composite
material.
Figure.3.5: Schematic diagram of an optical microscope
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3.6) Thermal Property Testing
3.6.1) Thermal Conductivity Testing
The thermal conductivity of composites were measured using Unitherm™ Model 2022 guarded
heat flow meter. The heat flow meter measures the thermal conductivity according to ASTM
E1530 standard. A schematic diagram showing the heat flow occurs in a heat flow meter is
shown in figure 3.6. A sample of the material was prepared in the shape of a round disk of 50
mm diameter and 5 mm thickness .Then it was held between two plates which were regulated at
a different temperature and a compressive load was applied. The lower surface would be portion
of a calibrated heat flux transducer. When the experiment started heat flows from the upper
surface through the sample to the lower surface, an axial temperature gradient was established in
the stack. The temperature difference across the sample along with the output from the heat flux
transducer was noted and thermal conductivity of the sample could be determined if the
thickness was known. A guard furnace surrounds the test stack to reduce the effect of heat
transfer through the edges of the sample that would cause an error in the measurement.
Figure.3.6: Schematic arrangement of guarded heat flow meter
Equations 3.5-3.7 were used to determine the thermal conductivity [31]:
Heat flow by conduction in one dimension=K (T1-T2)/x
(3.4)
Where Q is the heat flux (W)
K is the thermal conductivity of the body (W/m-K)
A is the cross sectional area (m2)
T1-T2 is the difference in temperature across the body (K)
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x is the thickness of the sample (m)
Thermal Resistance (m2-K/W) of sample is calculated by,
R   T1  T2  /  Q / A 
Kx/R
(3.5)
(3.6)
3.6.2) Thermo gravimetric Analysis
The thermal stability of the material as a function of temperature was measured using a thermo
gravimetric analyzer. In this test, the material was exposed to nitrogen atmosphere and the
sample was heated slowly at the rate of 10 °C/min. This results in thermal degradation of the
material and the corresponding weight loss was recorded. Figure 3.7 shows the schematic
arrangement of TGA setup. The final experimental result was generated in the form of graph
with mass percentage in ordinate and temperature in abscissa. TGA curve can gives the
information regarding the phase transition like vaporization, sublimation, decomposition etc. In
the case of natural fiber polymer composite the thermal stability is closely depend upon the
temperature. TGA helps in determining the thermal stability of PMC, which is responsible for
the factors like thermal expansion, thermal contraction and rate of moisture absorption [38].
Figure.3.7: Schematic arrangement of TGA set up.
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3.6.3) Differential Scanning Calorimeter
DSC was used to study the thermal transition of a polymer while heating. The test was
performed using METTLER TOLEDO DSC822e. The equipment had a simple arrangement for
two pans, out of which one pan was kept empty (reference pan) and other pan (sample pan)
contained the test specimen, as shown in figure 3.8. In this test the heat absorbed by the two pans
were compared. In order to maintain same temperature in both the pans, the heater has to deliver
extra heat into the non-empty pan. DSC experiment measures this extra amount of heat delivered
by the heater to the samples. The extra amount of heat delivered by the sample pan heater to
maintain the temperature equivalent to the reference pan was absorbed by the specimen and this
absorbed heat is the heat capacity of the material. This data was used to calculate the specific
heat capacity of the material. The glass transition temperature of the coir composites was also
determined using DSC.
Figure.3.8: Schematic arrangement of DSC
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CHAPTER 4
RESULTS AND DISCUSSIONS
This chapter contains the variation of mechanical and thermal behavior of coir epoxy composites
with respect to some factors like weight percentage of fiber, surface treatment of fiber and the
addition of cow dung power as an additive.
4.1) Mechanical Characteristics of Composites
4.1.1) Effect of fiber and filler concentration on hardness of composites
Vickers Micro hardness test had conducted for the composites of name given as C1, C2, C3, C4,
C8, C9, C10. Figure4.1 depicts that as the fiber weight percentage increases, the hardness value
of the both treated and untreated composites increases. This may be attributed to the fact that the
incorporation of fibers into the resin has lowered the mobility of the polymer chain in the rigid
composites [40]. The treated fiber composites exhibits better hardness compared to the untreated
ones. This may be due to the better dispersion of the coir fiber into the epoxy matrix as well as
the strong interfacial bonding between the fiber and the matrix.
Figure.4.1: Variation of Hardness of composite with respect to fiber loading
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The cow dung powder was added to the untreated 15% fiber loaded composite in a weight
percentage of 5, 10 and 15%. The measured hardness values is plotted in the graph, as shown in
figure 4.2. A slight increment in hardness value of 5 wt% cow dung powder composite is
observed. When the filler loading increases further to higher values of 10 and 15%, the hardness
of the composites seemed to decrease.
50
Hardness(Hv)
40
30
20
10
0
0
5
10
15
Cow dung powder loading(wt %)
Figure.4.2: Effect of Cow dung powder on hardness of the composite
4.1.2) Effect of fiber and filler concentration on tensile strength of the composites
Figure 4.3 shows the effect of fiber loading on both treated and untreated coir fiber reinforced
composites. It can be clearly observed that the tensile strength of the composites increases with
the increase in fiber loading. The stress strain behavior of any fiber reinforced composites
depends on many factors such as the effectiveness of the bonding between the matrix and fibers,
strength of matrix and fiber and volume fraction of fibers [41]. When the load is applied to the
composites, fibers acts as a load carrier, and matrix transfers the stress to the fibers uniformly
and effectively, thus resulting in good mechanical properties of composites. At higher fiber
content the composite exhibit better tensile properties due to presence of sufficient fibers which
withstand load. The result also shows that the treated composites exhibit higher tensile strength
than untreated composites. The alkali treatment of fibers lead to the removal of noncellulosic
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filler constituents and increased roughness of surface which helps in better bonding of the coir
fibers with the epoxy resin.
65
untreated fiber composites
treated fiber composites
60
55
Tensile Strength(MPa)
50
45
40
35
30
25
20
15
10
5
0
0
5
10
15
Fiber Loading (wt%)
Figure.4.3: Variation on Tensile Strength of composite with respect to fiber loading
Tensile Strength(MPa)
50
40
30
20
10
0
0
5
10
15
Cow dung powder loading (wt %)
Figure.4.4: Effect of Cow dung powder on Tensile Strength of Composite
Cow dung powder with 5, 10 and 15 wt% was added to 15 wt% untreated fiber composites and
the tensile strength was measured. From figure4.4, it is observed that the tensile strength of the
composite increases with the addition of cow dung powder up to 10% weight. When the loading
is further increased up to 15 wt% , the tensile strength of the hybrid composite tends to decrease.
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This is because the total reinforcement percentage of the composites increases which in turn
reduces the interaction between the reinforcement and matrix.
4.1.3) Effect of fiber and filler concentration on flexural strength of composites
Result of alkali treatment on the flexural properties of coir/epoxy composites with different fiber
loading (from 0 to 15 wt%) is plotted in Fig. 4.5. Initially the flexural properties are increasing
with the increase in fiber loading from 0 to 10 wt%, however at 15% fiber loading there is a
decreases in flexural strength. The reduction in mean flexural strength of 15 wt% coir fiber
reinforced composites may be due to the deficiency of epoxy resin which lead to the improper
wetting of the coir fibers. The treated fiber composites exhibited higher flexural strength in
compared to untreated one. This shows that the improved interfacial adhesion between the fiber
and matrix results in higher flexural strength of the treated composites.
untreated fiber composites
treated fiber composites
60
Flexural Strength(MPa)
50
40
30
20
10
0
0
5
10
15
Fiber Loading (wt%)
Figure.4.5: Variation on flexural strength of composites with respect to fiber loading
The effect of cow dung powder on the flexural strength of untreated coir-epoxy can be
interpreted by figure 4.6 .From figure, it could be observed that there is a gradual decrease in
flexural strength of the hybrid composite with respect to the filler loading. For untreated coirepoxy composite specimen flexural strength is 38.15 MPa, whereas for 5, 10 and 15 wt% of filler
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content in the composites flexural strength is 36.96 Mpa, 36.03 MPa and 34.11 MPa respectively
and indicating poor performance of composite due to filler-matrix interaction.
40
Flexural Strength(Mpa)
35
30
25
20
15
10
5
0
0
5
10
15
Cow dung powder loading(wt %)
Figure.4.6: Effect of Cow dung powder on Flexural Strength of Composite
4.1.4) Effect of fiber and filler concentration on impact strength of composites
The effect of fiber content on the impact strength is shown in figure 4.7. It is observed from the
figure that addition of fiber in the matrix leads to improved impact strength of the composites.
The impact strength increases with the increase in the fiber loading of the composites. The main
reasons of fiber fracture while impact loading is fiber fracture,fiber debonding and fiber pull
out.The energy dissipation in fiber pullout is much greater than the fiber fracture.So this is the
main reason for impact fracture in FRP.So as the fiber loading increases, impact strength
increases because more energy can be dissipated .In this case, fiber loading with 15%
concentration shows higher impact strength. [44]. In case of composites with higher fiber content
the chance of fiber pull-out is more. As the fiber content in composites increases, more energy
will be required for the weakning of the fiber matrix bonding or in other words more energy will
be absorbed by the fibers. The imact strength with the alkali treatment composites also. The
improvement in the impact strength of alkali treated composites may be due to presence of low
moisutee in fibers due to which strong interfacial adhesion between fiber and matrix is possible.
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untreated fiber composite
treated fiber composite
0.40
0.35
Impact energy (J)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
5
10
15
Fiber Loading(wt%)
Figure.4.7: Variation of impact strength of composites with respect to fiber loading
0.35
Impact Energy(J)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
5
10
15
Cow dung powder loading (wt%)
Figure.4.8: Effect of cow dung powder on impact strength of composite
The effect of cow dung powder weight percentage on impact strength of composite is shown in
Figure 4.8. From the figure 4.8, improvement in the impact strength of the composites is
observed with the addition of filler. Similar observation has been reported by the researchers in
case of oil palm wood flour filled glass epoxy composites [45]. Authors explained that the
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improvement of the impact strength of the composites is due to cushioning effect provided by the
natural fillers.
4.2) Optical microscopic images
Figure.4.9: Optical Microscopic images of composites.
The images shown above are the optical microscopic images of various samples. In figure
4.9,sample (a) & (b) are the images surface view of untreated fiber composites of
fiber
concentration 5% and 15% respectively(C2 and C4).The images shown in (c)&(d) are the treated
fiber composite of same fiber concentration (C8 and C10)mentioned above. Images (e) & (f) are
the end surface view of C2 and C4 after tensile testing .And the images (g) & (h) are the end
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view of sample C8 and C10 after tensile testing. The images (a) and (c) are the composite of
same concentration (5%) of untreated fiber and treated fiber respectively. We can observe that
there is a color difference between these two the treated fiber is seems as somewhat yellowish
compare to pale light brown coloured untreated fiber. This colour change is due to The colour
change of fibre of (a) and (b) pale brown to yellow was observed due to removal of lignin.
4.3) Thermal Characteristics of Composites
4.3.1) Effect of fiber concentration and the addition of cow dung powder on Transverse
Thermal Conductivity of composite.
The resultant variation of the thermal conductivity of composite with respect to fiber loading is
shown in the figure 4.10. From the figure it is observed that the thermal conductivity of the
composites decreases with the increases in fiber loading. On comparing with pure epoxy matrix,
it has been found that the thermal conductivity of composites decreased by 19.08%, 31.90% and
42.45% for the composites with 5, 10 and 15 wt% fiber loading, respectively. From the above
observation it can be concluded that the thermal insulating behaviour of the composites increases
with increase in fiber loading. The natural fiber coir has a hollow portion which contains air. The
air has a low thermal conductivity of 0.026 W/m-K at 25 °C and thus offer an excellent heat
insulating effect. The percentage of air increases with the increasing fiber loading of the
composites and results in the reduction of thermal conductivity of the composites [46].
untreated fiber composite
alkali treated fiber composite
0.36
Thermal conductivity(W/m-K)
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0
5
10
15
Fiber Loading (wt%)
Figure.4.10: Significance of fiber loading on thermal conductivity of composite
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The thermal conductivity of alkali treated composites with different fiber loading were also
determined. It is observed that, there is a slight increase in thermal conductivity of treated
composite samples compared to the corresponding untreated one. The alkali treatment of the
fibers practically removes all the noncellulose components except waxes. The dissolution of
lignin by NaOH led to formation of small pores on the surface of the fibers, thus improving the
area of contact between the matrix and fiber [47]. Thus resulting in increased thermal
conductivity of the treated coir fiber composites. From the thermal insulation point of view
untreated coir fiber composites are more efficient compared to the treated composites. Figure 4.3
shows, composites with 15% untreated fiber loading (C4) has the lowest thermal conductivity.
To further reduce the thermal conductivity of the coir fiber composites cow dung powder with 5,
10 and 15 wt% was added to 15 wt% untreated composites. The thermal conductivity of these
samples are plotted in figure 4.11. It is observed that the addition of cow dung powder results in
reduction of thermal conductivity of the untreated composites. Similar observation has been
reported by the authors [30] in case of cow dung powder filled glass–polyester hybrid
composites. The thermal conductivity values of the untreated coir fiber composites having 0-15
wt% of cow dung powder decreases from 0.202 - 0.168 W/m-K. The thermal conductivity of the
pure epoxy matrix is reduced by 52.13% o on adding 15 wt% cow dung powder to the untreated
composites i.e. C7 sample.
0.205
Thermal conductivity(W/m-K)
0.200
0.195
0.190
0.185
0.180
0.175
0.170
0.165
0
5
10
15
Cow dung powder Loading(wt%)
Figure.4.11: Variation of thermal conductivity of composite with respect to the addition of cow
dung powder
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4.3.2) Thermo gravimetric Analysis
In the TGA the thermal degradation phenomena of treated and untreated coir epoxy composite
had been studied. From figure 4.12, it can be observed that at lower temperature weight loss
occurs more in the case of untreated fiber composite compared to treated fiber composites. The
untreated coir fiber has higher moisture content due to the presence of hemicellulose and lignin.
Thus, the relative weight loss is higher in untreated fiber composites. In untreated composites,
most of the moisture is present in between the interface region of fiber and matrix.
During the test, when untreated fibers were subjected to heating, the evaporation of large amount
of moisture present would take place and due to this weight loss occurs more in case of untreated
composites. However in alkali treated fiber reinforced composites, the hemicellulose content was
less and the moisture absorbed was also low [11]. At higher temperature the weight percentage
of untreated composite was found to be larger than the treated composite. This was because of
the presence of lignin in the untreated fiber, which were responsible for the formation of char.
Thus, the optimum removal of lignin content is required to attain balance between positive
property of formation of chars and the negative impact of low temperature degradation [48].
untreated fiber composite
treated fiber composite
100
Weight %
80
60
40
20
0
0
100
200
300
400
500
600
0
Temperature( C)
Fig.4.12: Comparison on thermal stability of alkali treated and untreated fiber filled composites
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4.3.3) Effect of fiber concentration and the addition of cow dung powder on Specific Heat
Capacity of composite
Specific heat capacity of a material is the quantity of heat required to increase the temperature of
unit mass of the substance by 1 K. For higher specific heat materials, more energy is needed to
raise their temperature. The specific heat capacity of composites is measured by DSC method.
The specific heat capacity of the polymers can be increased by adding fibers. Thus, fiber
reinforced composited can be used for insulation purposes.
1200
untreated fiber composite
treated fiber composite
Sp.Heat Capacity (J/Kg/K)
1100
1000
900
800
700
600
500
400
0
5
10
15
Fiber Loading(wt%)
Figure.4.13: Variation of specific heat capacity of composite with respect to fiber concentration
The specific heat capacity of the treated and untreated fiber composites at different fiber loading
are represented in figure 4.13. It is observed that the untreated fiber composites exhibits better
specific heat capacity than the treated composites. The treated fibers contains less moisture as
majority of the hemicellulose is removed on treatment. The specific heat capacity of water is
much higher than that of the polymers. The specific heat capacity of water is 4180 J/Kg/K. More
the moisture or water content in a material more is the specific heat capacity of that material. As
untreated composites contains more moisture they exhibit higher specific heat capacity compared
to the treated composites. The untreated fiber composite with 15% fiber content (C4) showed
higher specific heat capacity, as observed from the figure 4.6. Further improvement in the
specific heat capacity of the composites is achieved by adding cow dung powder into C4. From
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figure 4.14, it is observed that the increase in cow dung powder concentration results in
increased specific heat capacity of the untreated composites. The composites with 15 wt% cow
dung powder exhibits higher specific heat capacity.
1300
Sp.heat Capacity(J/Kg/K)
1280
1260
1240
1220
1200
1180
1160
1140
1120
0
5
10
15
Cow dung powder Loading (wt%)
Figure.4.14: Effect of cow dung on Specific Heat Capacity of composite
4.3.4) Effect of fiber concentration on Glass Transition temperature of composite
The glass transition temperature (Tg) is a particular temperature below which the polymer
behaves as hard and brittle material like glass, and if temperature exceeds Tg, polymer behaves
like rubbery material or viscous fluid. The glass transition is a transition that occurs to
amorphous polymers, whose chains are not organized as ordered crystals. When the temperature
is above Tg, the polymer chains can move around effortlessly. On applying the transverse force
to bend polymer samples, the molecules show the tendency to move into new positions to relieve
the stress that is applied on them. But, if force is applied to bend sample of a polymer which is
kept below its Tg, the polymer chains cannot be able to move into new locations to relieve the
stress that applied on that.
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untreated fiber composites
treated fiber composites
Glass Transition Temperature (0C)
76
74
72
70
68
66
64
0
5
10
15
Fiber Loading (wt%)
Figure.4.15: Effect of fiber concentration on Glass Transition Temperature of Composite.
The glass transition temperature of coir epoxy composite was determined using differential
scanning calorimeter. Figure 4.8 shows the glass transition temperature of both treated and
untreated coir-epoxy composites with varying fiber loading. It is observed that that Tg of
composites increases with increase of fiber quantity. Higher Tg temperature is observed in case
of composites with 10 wt% fiber loading. When fiber is added to the matrix, it would obstruct
the mobility of the polymer and thereby more energy required to break the immobility of
polymer. So the Tg is increasing initially. And when the fiber content exceeds a certain limit
(here more than 10%) a decreasing tendency of Tg is observed. The quantity or amount of
moisture will increase when large amount of natural fibers are added to the composites. The
higher moisture content in the composites might disrupt the bond between fiber and matrix and
with this effect polymer chain segment mobility could be increased [49]. The glass transition
curve with respect to fiber loading of both treated and untreated composites shows similar trend.
However, the glass transition temperature of treated coir composites is much higher compared to
untreated composites. Due to surface treatment of fiber, reduction in fiber moisture and strong
interfacial bonding between fiber and matrix takes place which in turn improve the glass
transition temperature of treated composites. The untreated composite with 5 wt% of filler
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M Tech Thesis
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loading exhibits maximum glass temperature of 67.5 ˚C, as observed from figure 4.16. But the
glass transition temperature of composites decreases with further addition of cow dung powder
in the composites.
68.0
Glass Transition Temperature(0C)
67.5
67.0
66.5
66.0
65.5
65.0
64.5
0
5
10
15
Cow Dung Powder Loading (wt%)
Figure.4.16: Effect of cow dung on Glass Transition Temperature of composite
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CHAPTER 5
CONCLUSION
A detailed study has been conducted on the thermal and mechanical behavior of coir/epoxy
composite on the basis of different weight concentration of fiber and filler. Alkali treatment of
the coir fiber has also been done. The study led to the conclusions mentioned below.
1. Epoxy resin reinforced with alkali treated fiber and untreated fiber has been fabricated by
hand lay-up method. Coir/Cow dung powder/Epoxy hybrid composite had also fabricated
with same technique.
2. In tensile testing, as the fiber concentration increases, tensile strength of composite
increases. It is also found that alkali treated fiber loaded composites shows excellent
tensile strength compared to untreated one. As a result, the maximum tensile strength
obtained in case of 15 wt.% fiber loaded composite and it showed almost 48% higher
value compared to respective untreated one. When cow dung powder was added to the
composite of untreated fibers, the hybrid composites with 10 wt% of cow dung powder
exhibits higher tensile strength.
3. In flexural testing similar behavior were also obtained. Flexural strength increases with
fiber concentration and here maximum value obtained is at 10% fiber concentration.
When the concentration of fiber increases further, flexural strength decreases.
4. Micro hardness also exhibits the similar character as that of tensile and flexural strength.
It increases with fiber loading and surface treatment. Maximum hardness obtained on
15%fiber loaded treated composite.
5. In the testing of impact strength, it was observed that the impact strength increased with
increase of fiber loading. Impact strength of the coir-epoxy composite is enhanced by
alkali treatment. When cow dung powder was added to untreated version, the impact
strength were increased further.
6. Thermal conductivity was tested with heat flow meter and it was observed that
conductivity decreases with the increase of fiber concentration. When surface treated coir
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fiber composites were compared with untreated fiber composites, lower thermal
conductivity was shown by untreated coir fibers.
7. As the cow dung powder added to composites thermal conductivity decreased further to
lower values. The highest thermal insulation property was shown by hybrid composite
containing 15 wt% untreated coir and 15 wt% cow dung powder.
8. Specific heat capacity of the composites were tested with DSC and it was observed that
as fiber loading was increased, specific heat capacity of the composite also increased.
Untreated fiber composites showed higher specific heat capacity compared to treated
fiber composites because untreated fiber contain more water. The effect of cow dung
powder also enhanced the value of specific heat capacity.
9. Rate of decomposition of treated and untreated fibers were carried out by TGA .In low
temperatures decomposition rate or weight loss is higher for untreated fiber composites
When the temperature crossed 5500C residue content in untreated fiber composite was
higher compared to untreated one because of the presence of lignin in untreated fiber,
which was responsible for the formation of char.
10. Glass transition temperature (Tg) was also tested by DSC .It was found that Tg increases
with increasing fiber concentration up to 10% fiber loading and there after Tg decreases.
5.1) Scope for future work
There is a wide scope for future to scholars to explore the current research field. The
present work can be further continued to study other aspects of composites like,
 Use of other natural fibres and their behavior on the basis of same parameters
used here,
 Study of composite properties on the basis of different fabrication techniques
other than hand lay-up method like spray up method, compression molding
method, filament winding method etc. can be done.
 Evaluation and optimization of tribological, electrical, physical properties etc. and
the experimental results can be analyzed.
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