STUDY OF WATER ABSORPTION BEHAVIOUR OF NATURAL FIBRE REINFORCED COMPOSITES

STUDY OF WATER ABSORPTION BEHAVIOUR OF NATURAL FIBRE REINFORCED COMPOSITES
STUDY OF WATER ABSORPTION BEHAVIOUR OF NATURAL
FIBRE REINFORCED COMPOSITES
A Thesis Submitted to
National Institute of Technology, Rourkela
In partial fulfilment of the requirement for the degree of
Master of Technology
in
Mechanical Engineering
By
NANDKISHOR SHARMA
(Roll no. 212me1283)
Department of Mechanical Engineering
National Institute of Technology
Rourkela-769008
India
STUDY OF WATER ABSORPTION BEHAVIOUR OF NATURAL
FIBRE REINFORCED COMPOSITES
A Thesis Submitted to
National Institute of Technology, Rourkela
In partial fulfilment of the requirement for the degree of
Master of Technology
In
Mechanical Engineering
(Specialisation-Machine Design and Analysis)
By
NANDKISHOR SHARMA
(Roll no. 212me1283)
Under the guidance and supervision of
Prof. S. K. ACHARYA
Department of Mechanical Engineering
National Institute of Technology
Rourkela-769008
India
DEPARTMENT OF MECHANICAL ENGINEERING
NATINAL INSTITUTE OF TECHNOLOGY
ROURKELA, ORRISA
INDIA- 769008
CERTIFICATE
This is to certifythat the thesis entitled “Investigation of mechanical properties of luffa
cylindrica reinforced epoxy composite for different environmental conditions” submitted
to the National Institute of Technology, Rourkela by Nandkishor Sharma, Roll No.
212ME1283 for the award of the degree of Master of Technology in Mechanical
Engineering is a record of bonafied research work carried out by him under my supervision
and guidance. The results presented in this thesis hsa not been, to the best of my knowledge,
submitted to any other University or Institute for the award of any degree or diploma.
The thesis, in my opinion, has reached the standards fulfilling the requirements for the award
of the degree of Master of Technology in accordance with regulations of the Institute.
Place: Rourkela
(Dr. S. K. Acharya)
Date:
Professor
Department Mechanical Engineering
National Institute of Technology
Rourkela – 769008
i
ACKNOWLEDGEMENT
I would like to express my gratitude to my supervisor Prof. S.K. Acharya for
his guidance, encouragement, moral support and affection through the course of my work.
I am also thankful to Prof. Sunil Kumar Sarangi, Director, NIT, Rourkela who
took keen interest in the work. My special thanks to Prof. K.P Maity, Head of
Mechanical Engineering Department and all staff members of the mechanical department
for their timely help in completion of this work.
I am also thankful to Mrs. Niharika Mohanta of mechanical engineering for her
support & help during my experimental work.
This work is also the outcome of the blessing guidance and support of my father
and mother Mr. Sharda Prasad and Mrs. Binda Devi this work could have been a
distant dream if I did not get the moral encouragement from them.
I feel pleased and privileged to fulfil my parent’s ambition and I am greatly
indebted to them for bearing the inconvenience during my M-Tech course. I express my
appreciation to my friends for their understanding, patience and active co-operation
throughout my M-Tech course finally.
(NANDKISHOR SHARMA)
ii
DECLARATION
I hereby declare that this submission is my own work and that, to the best of my knowledge
and belief, it contains no material previously published or written by another person nor
material which to a substantial extent has been accepted for the award of any other degree or
diploma of the university or other institute of higher learning, except where due
acknowledgement has been made in the text.
(NANDKISHOR SHARMA)
iii
ABSTRACT
Environmental perception today encourages empiricism worldwide on the learning of plant or
natural fibre reinforced polymer composite and cost efficient alternative to synthetic fibre
reinforced composites. The accessibility to natural fibers and simplicity in manufacturing
have persuaded researchers to aim for locally existing low cost fibers and to investigate their
possibility of reinforcement intensions and up to what extent they can satisfy the essential
detailing of superior reinforced polymer composite intended for different application
program. Natural fibre represents a superior biodegradable and renewable alternative to the
most popular synthetic reinforcement, i.e. glass fibre possessing high mechanical properties
and low cost. Regardless the curiosity and environmental request of natural fibers, there
usage is restricted to non-bearing uses, because of its lower strength than that of synthetic
fibre reinforced polymer composite. The stiffness and strength limitations of bio composites
can be chased by operational arrangement by placing the fibers at particular locations to have
higher strength performance. Research regarding preparation and properties of polymer
matrix composite (PMC) replacing the synthetic fibre with natural fibre like Jute, Sisal, Jute,
Bamboo, Pineapple, Bagasse and Kenaf were carried out. Renewable, environmental
friendly, low cost, lightweight and high specific mechanical performances are the advantages
of these plant fibres over the glass fibre or carbon fibre. Composites are exciting materials
which
are
finding
increasing
application
in
transportation,
aerospace,
defence,
communication, sporting, electronics and number of other commercial and consumer
products. Composite materials have become one of the fastest growing research and
development areas of Material Science because of their high potential. In current years there
is swift growth in the arena of fibers, matrix, materials, processing, boundary structure,
bonding and their characteristics on the final properties of composites. The technological
developments in composite materials help in meeting the global industrial demand for
materials with improved performance capabilities.
Keeping this in view the present work has been under taken to develop a
polymer matrix composite (epoxy resin) using Luffa Cylindrica fibre and to study its
moisture absorption behavior and mechanical properties. The composite are prepared
with different volume fraction (number of layers) of Luffa Cylindrica fibre.
iv
TABLE OF CONTENTS
Certificate .................................................................................................................................. i
Acknowledgement .................................................................................................................... ii
Declaration...............................................................................................................................iii
Abstract ………..………………………………………………………………………….....iv
Table of Content ...................................................................................................................... v
List of Tables .........................................................................................................................viii
List of Figures ......................................................................................................................... ix
Chapter-1
Introduction
1.1
Background
1
1.2
Composites
2
1.2.1
Why a composite?
2
1.2.2
What is a composite?
3
1.2.3
Classification of composites
4
1.2.3.1
Particulate composites
6
1.2.3.2
Fibrous composites
6
1.3
1.4
Components of a Composite Material
6
1.3.1
Role of matrix in a composite
6
1.3.2
Materials used as matrices in composites
7
1.3.2.1
Bulk-Phases
7
1.3.2.2
Reinforcement
7
1.3.2.3
Interface
7
Types of Composite Materials
8
1.4.1
Fibre-Reinforced Composites
8
1.4.1.1
8
Continuous or long fiber composite
v
1.4.1.2
1.4.2
1.5
Laminate Composites
Natural Fiber Composites: (Initiative in Product Development)
1.5.1
Chapter 2
2.1
2.2
2.3
Applications of natural fibre reinforced composites
9
9
10
11
Literature Survey
Natural Fibers: Source and Classification
Chemical Composition of Natural Fibers
14
16
2.2.1
Cellulose
16
2.2.2
Hemicelluloses
16
2.2.3
Lignin
17
2.2.4
Pectin
17
Matrix Material
2.3.1
Chapter-3
Discontinuous or short fiber composite
18
Thermo-sets
19
Mechanical Characterization of Luffa Cylindrica Fibre Epoxy
Composite
3.1
Introduction
21
3.2
Chemical Modification of Fibre
24
3.2.1
Methods of Chemical Modifications
3.2.1.1
3.3
Alkaline treatment
Composite Fabrication
25
26
vi
3.4
3.3.1
Preparation of Luffa Cylindrica Fibre Mats
26
3.3.2
Epoxy resin
26
3.3.3
Composite preparation
26
Study of Environmental Effect
3.4.1
Moisture absorption test
28
3.4.2
Mechanical testing of samples
29
3.4.2.1
Tensile test
29
3.4.2.2
Flexural test
31
3.4.3
3.4.3
3.5
Chapter-4
28
Results and discussion
32
3.4.3.1
Moisture absorption behaviour
32
3.4.3.2
Measurement of diffusivity
33
Effect of moisture absorption on Mechanical properties
34
Conclusions
35
References
81
vii
LIST OF TABLES
Table No.
Title
Page No.
1.1
Classification of composite
5
2.1
Properties of glass and natural fibers
15
2.2
Comparison between Natural fibre and Glass fibre
18
3.1-3.24
Variation of weight gain and thickness swelling of untreated
and treated Luffa Cylindrica fibre epoxy composite
(flexural and tensile) with immersion time expose at distil
and saline water environment.
viii
36-59
LIST OF FIGURES
Figure No.
Title
Page No.
1.1 (a-e)
Different types of Composite
10
1.2
Photographs of Luffa Cylindrica plant and luffa mat
12
2.1
Classification of natural fiber that can be used as
15
reinforcements
2.2
Chemical structure of DGEBA
19
3.1
Mould used for fabrication
27
3.2 (a)
Flexural test samples
27
3.2 (b)
Tensile test samples
28
3.4 (a)
UTM machine sample unloaded for tensile testing
30
3.4 (b)
UTM machine sample loaded for tensile testing
30
3.5
UTM machine sample unloaded for flexural testing
31
3.6 to 3.13
Variation of flexural and tensile strength with different
layers of Luffa Cylindrica fibre epoxy composites (untreated
and treated) exposed to distil water environment
ix
62-65
3.14 to 3.21
Variation of thickness swelling of untreated and treated
66-69
Luffa Cylindrica fibre epoxy composite (tensile and flexural)
with immersion time expose to saline and distil water
environment
3.22 to 3.29 Variation of weight gain of untreated and treated Luffa
70-73
Cylindrica fibre epoxy composite (tensile and flexural) with
immersion time expose to saline and distil water
environment
3.30 to 3.33
Maximum moisture absorption of untreated and treated
74-75
Luffa Cylindrica fiber epoxy composite (tensile and flexural
samples) versus fiber loading in both the environments
3.34
Example Diffusion curve fitting for Luffa Cylindrica fibre
76
epoxy composites under different environment
3.35
Example Plot of percentage of moisture absorption versus
square root of time for calculation of Difusivity
3.36 to 3.43 Variation of log (Mt/Mm) with log t for untreated and
treated Luffa Cylindrica fiber epoxy composites (tensile and
flexural) exposed to distil and saline water environment
x
77-80
Chapter 1
INTRODUCTION
Chapter-1
1.1 BACKGROUND
It is a platitude that technological advances depends on fosters in the sector of materials. If
sufficient materials to bear the service loads and conditions are not available then one does
not have to be a skilful to realize the most advanced turbine or air-craft pattern. Whatsoever
the field may be, the ultimate restriction on progression is to be governed by materials.
Composite materials in this regard signify a big step in the constant accumulation of
optimization in materials. Composites are mixture of two or more materials such as
reinforced plastics, metals, or ceramics. The reinforcements may be in the form of fibers,
particles, whiskers or lamellae and are embedded in a suitable matrix, thereby providing a
material that contains the most useful properties of the constituents. High structural
strength, glass fibre reinforced plastics were developed in the early 1940’s and the
application of reinforced plastics composites, the glass fibre provides strength and stiffness
while the plastic matrix provides the temperature capabilities of the composite. Initially the
glass fibres were incorporated in a polyester matrix which could withstand temperature up
to 200⁰C. They were applied in car bodies, appliances, boats etc., because of their light
weight and mitigate of production. Intricate composites parts can be made by injection
moulding. Polymer matrices are usually thermosets such as epoxies. Later, resins which can
withstand high temperatures, of the order of 300⁰C were developed such as polyamides.
Other thermo setting resins include benzocylobutene – bismaleimides. Advanced
composites are manufactured by using the above polymers with reinforcements of stronger
fibres such as aramid and carbon. As a result advanced composites are finding increasing
applications in aircraft, automotive industry, etc. In order to reduce the manufacturing time,
thermoplastics polymers such as polyether – ether ketone (PEEK) have been developed. The
plastic requires only a short revelation to heat to soften the plastics, thereby allowing faster
processing of the composite.
The limitations of the polymer matrix composites at high temperatures can be overcome by
the use of metal matrix composites. These composites are processed by powder metallurgy
methods, by penetration of the molten metal with the fibre or particulate or by mixing
particulates with molten metal. Plasma spraying, vapour deposition, plasma spraying or
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electro deposition followed by dispersal bonding are the other methods of fabrication. Metal
matrix composites are discovering applications in defence, aerospace, automotive and
electronic packaging. In addition to metal matrix composites, intermetallics such as nickel,
iron, titanium and niobium aluminides matrix composites are also being actively considered
for use at elevated temperatures.
The temperature range of application of metal matrix composites is lower than that
of ceramic matrix composites. Ceramic matrices such as zirconia, alumina, silicon nitride,
silicon carbide, mullite etc. can be reinforced with ceramic continuous fibres, whiskers or
particulates. Carbon-carbon composites is a ceramic composite which can retained its
strength at temperatures up to 2500⁰C and is applied as a critical component in aerospace.
Adduce composites have both structural and functional applications. Adaptable composites
will have the potentiality not only of load bearing but will also have an agile and flexible
response to structure functional conditions. These advanced growths will increase and
sensing potential of structures such as vertical tails, aircraft bulkheads, intrinsic avionics,
smart skins and antenna systems. For elevated temperatures, smart metal matrix composites
with fibre optic sensors in a titanium matrix composite are being boisterously considered.
The study of composites materials is a multifaceted memorandum as it is difficult
for any individual to grasp the compound behaviour of many of the current composites. This
field provides lot of analytical problems for experimental schedules, theoreticians for
research workers and new defiance for designers. Even the technologically advanced fibre
glass reinforced plastics in the 1940s require a information of ceramics, glass technology,
surface science, polymers, modelling, design and analysis in order to redeem the properties,
structure and purpose of the final composite product.
1.2 COMPOSITES
1.2.1 Why a composite?
Over the last three decades years composite materials, plastics and ceramics have been the
ascendant developing materials. Numerous uses of composite materials have grown evenly,
pervasive and dominant new markets interminably. Modern composite materials comprise a
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significant amount of the engineering materials market varies from commonplace products
to worldly niche applications.
Although composites have already manifested their value as weight reduction
materials, the existing job is to make them cost productive. The endeavours to yield
economically smart composite components
have evolved in some unorthodox
manufacturing techniques currently being used in the composite industries. It is vibrant,
specifically for composites, that the development in manufacturing technology only is not
sufficient to overcome the cost hurdle. It is important that there must be an unsegregated
implementation in material processing, designing, manufacturing, tooling, quality assurance
and even programmes organisation for composites to make them competitive with metals.
Further, need of composites for lighter building materials and more shock resilient
structures has placed high prominence on the usage of fresh and innovative materials that
not only reduces weight but also assimilates the shock and vibration by tailored
microstructures. Composites at the present are largely used for rehabilitation or
strengthening of preceding structures that need to be render in order to make them seismic
resilient, or to restore damage due to seismic activities.
The properties of composite material can be designed by bearing in mind the
structural aspects, unlike conventional materials (e.g., steel); both material and structural
design operations are there in the plan of a structural component using composites.
Properties of composites such as thermal expansion, stiffness etc. can be assorted frequently
over a wide range of values beneath the designer control. Correct assortment of
reinforcement category allows concluded product features to be customized nearly every
specific engineering necessity.
1.2.2 What is a composite?
A typical composite material consists of two or more materials (bonded and mixed) on
macroscopic rules which are not soluble in each other.
Normally, a composite materials are composed of reinforcement (fibers, flakes,
particles and fillers) implanted in a matrix such as polymers, metals, or ceramics. The
function of matrix is to hold the reinforcement to form the craved shape while the
reinforcement ameliorates the whole mechanical properties of the matrix. The new
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combined material possesses better strength than the each individual material in a system,
when designed correctly.
As stated by Jartiz, [1] Composites are such a universal material which can provide
such properties that are not possible to obtain from any distinct material. Composites
possess cohesive structures brought up by physically amalgamating two or more suited
materials, but different in composition and characteristics and occasionally in configuration.
Kelly [2] evidently emphasises that the composites should not be considered as just
combination of two different materials. In wider sense; the amalgamation has its particular
characteristic properties. In relations of strength, heat resistant or specific other advisable
quality, it is far better than the components taken individually or fundamentally different
from both of them.
Berghezan [3] defines as “The composites are amalgamated materials which differ
from alloys by the fact that the individual components in composites preserve their
characteristics but are combined in such a way so as to take advantage of their features only
and not of their limitations”, in order to obtain a much better material.
Van Suchetclan [4] describes composite materials as diverse materials which consist
of two or more solid states that are in constricted interaction with each other. He also stated
that composites can be also contemplated as homogeneous material on a microscopic level
in a way that whichever part of it is separated will have the physical property same as the
composite.
1.2.3 Classification of Composites
Composite materials perhaps categorized in distinct ways [5]. Arrangement based on
the geometry of a characteristic unit of reinforcement is suitable since it is the geometry of
the reinforcement which is liable for the mechanical properties and better presentation of the
composites. The classification is presented in Table1.1. The two broad classes of
composites are:
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(i)
Fibrous composites
(ii)
Particulate composites
Page 4
Table-1.1
Classification of composite
Composite materials
Fibre reinforced composites
Multi layered
composites
Single layer
composites
Continuous fibre
reinforced
composites
Unidirectional
reinforcement
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Discontinuous fibre
reinforced
composites
Random
orientatio
n
Laminates
Particle reinforced composites
Random orientation
Preferred orientation
Hybrids
Preferred
orientatio
n
Bi-directional
reinforcement
Page 5
1.2.3.1
Particulate Composites
The name only specifies, that the reinforcement posses particle nature. It may be
cubic, spherical, tetragonal, or of any regular or irregular shape, but it is approximately
equiaxial. In common, particulates are not much productive in enhancing fracture resistance
but it increases the stiffness of the composite to a restricted amount. Particle fillers are largely
used To upgrade the properties of matrix materials such as to improve the electrical and
thermal conductivity, to improve presentation at high temperatures, abrasion resistance,
decrease friction, improve wear, increase surface hardness, increase machinability and
lessens shrinkage.
1.2.3.2
Fibrous composites
Fibres are well known for its length and cross-section ratio i.e. their length is much
greater than that of cross-sectional dimensions. The reinforcement dimension plays a
significant role in governing its potentiality of contributing properties to the composites.
Since reinforcement possessing a long dimension depresses the growth of developing cracks
usual to the reinforcement that might results to wreck, especially with brittle matrices as
fibers are very effectual in enhancing the fracture resistance of the matrix.
1.3 COMPONENTS OF A COMPOSITE MATERIAL
In its most basic form a composite is the element which comprises of two or more
elements (at least two elements) that are binded together to produce a different material
which produces enhanced properties that are better and different to the properties of the
individual elements. Usually composites comprises of reinforcement and a matrix,
incorporated mainly to raise the stiffness and the strength of the matrix.
1.3.1 Role of matrix in a composite
Numerous materials when are in a fibrous form display very high strength but in order
to attain these properties the fibers must be joined by an acceptable matrix. The role of matrix
is to separates the fibers from each other in order to avert abrasion and development of fresh
surface flaws and to stick the fibers in place by acting as a bridge. A quality matrix must
possess the capability to transfer the load onto the fibers, deform easily under applied load.
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In case of laminates [6] the nature of bonding forces indicates that upon initial loading
there is a proneness for the adhesive bond between the matrix and reinforcement to be failed.
The frictional forces between them portrayal for the high strength properties of the laminates.
1.3.2 Material used as matrices in composites
1.3.2.1 Bulk-Phases
(a) Metal Matrices
(b) Polymer Matrices
(c) Ceramic Matrices
1.3.2.2
Reinforcement
In a composite material the purpose of the reinforcement is basically to increase the
mechanical properties of the neat resin structure. The properties of the composite are affected
differently by different fibers used in it as these fibers have different properties. For various
applications, the fibres are required to be organised into the structure of sheet, known as a
fabric, in order to make handling possible.
1.3.2.3
Interface
The important feature of interface is that its properties are not rendered by any
component in the system on isolation. It is a bounding zone at which disturbances occurs, it
can be mechanical, chemical, physical etc. It is required that fibre must be wetted by the
matrix material and in order to improve this wettability coupling agents are used frequently.
Increase in the interface surface area is only possible when the fibre is well ‘wetted’. The
applied load must be effectually transferred to the fibers from the matrix through the interface
to get the advisable properties and this concludes that the interface should be large and the
fibers and matrix must be joined strongly.
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1.4 TYPES OF COMPOSITE MATERIALS
The composite materials are classified into the following categories as shown in
Figure-1.1 (a - e).
1.4.1 Fibre-reinforced composites
Because of intrinsic high specific strength and stiffness these composites are
universally used in numerous industrial applications. These composites are acquiring high
potential in tribological applications also as they possess brilliant structural presentation.
Fiber reinforced composites materials comprises of fiber of high strength in or bonded to a
matrix with discrete interfaces between them [4, 5]. In this form physical and chemical
identities are retained by both fibres and matrix. Yet they produce an amalgamation of
properties which is difficult to achieve with either of the composite constituents individually.
In general, the role of fibers is to carry load, whereas the role of matrix is to keeps them in the
crave position and alignment [5, 6].Fibrous composite can be further classified into two
groups: continuous (long) fiber composite and discontinuous (short) fiber composite.
1.4.1.1
Continuous or long fiber composite
Geometrically, a continuous fibre is distinguished as it possesses a high length to
diameter ratio. It also comprises of reinforcement matrix by a disseminate phase in the type
of continuous fibre. These are basically tougher and stiffer when compared to matrix i.e. bulk
phase material. Based on the manner in which fibers are stuffed within the matrix, it is again
subdivided in to two categories: (a) unidirectional reinforcement and (b) bidirectional
reinforcement. In unidirectional reinforcement, the fibers are aligned in one direction only
where as in bidirectional reinforcement the fibers are aligned in two directions either at some
desired angle (angle-ply) or at right angle to one another (cross-ply). When fibers are
continuous and large, they transmit certain degree of anisotropy to the properties of the
composites especially when they are oriented. Multi-axially oriented continuous fibre
composites are also exhibit near isotropic properties.
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1.4.1.2 Discontinuous or short fiber composite
Short-fiber reinforced composites comprises of a reinforced matrix by a distributed
phase in the type of discontinuous fibers which are having, length < 100×diameter. The low
cost, proficiency of fabricating intricate parts, and isotropic nature are sufficient to make the
short fiber composites the material of selection for large-scale production. Accordingly, the
short-fiber reinforced composites have profitably established its place in lightly loaded
component production. Furthermore the discontinuous fiber reinforced composite divided
into: (a) biased or preferred oriented fiber composite and (b) random oriented fiber
composite. In the prior, the fibers are oriented in pre-decided directions, whereas in the later
type, fibers remain randomly. The alignment of short fibers can be done by scattering of fiber
on to given plane or inclusion of matrix in liquid or solid state before or after the fiber
displacement.
1.4.2 Laminate Composites
Laminate Composites consists layers of material held together by matrix. Mainly,
these layers are organized alternatively in order to provide a better bonding between the
reinforcement and the matrix. According to the end use of the composite these laminates can
have uni- directional or bi-directional orientation of the fiber reinforcement. The different
types of composite laminates are angle-ply, unidirectional, symmetric laminates and crossply. A blended laminate can also be fabricated by the use of alternate constituent materials or
of the same material with alternate reinforcing design. In most of the applications of laminate
composites, man-made fibers are used because of their good amalgamation of physicomechanical and thermal behaviour.
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(a) Continuous fiber
(b) Particulate composites
(c) Flake composites
composite
(d) Random fiber (short fiber) Composite
Figure-1.1 (a-e)
(e) Laminate Composite
Different types of Composite
1.5 NATURAL FIBER COMPOSITES: Initiative in Product Development
The cost effective option to synthetic fibre reinforced composites and the interesting
studies of plant or natural fibre inspires the researchers to make advances in the field of
composites. Ease in access and built-up simplicity of natural fibre have convinced these
researchers to try natural fibres which are available locally and to study their practicability of
reinforcement motives. These are also studied to have the information that up to what limit
they can fulfil the desired specifications and properties for various uses. Natural fibre appears
as a good renewable and biodegradable substitute to most of the synthetic fibre such as glass
fibre.
Vegetables, animal, mineral fibers etc. fall under the area of natural fibre. Generally it
is referred as wood and agro based fibre, leaf, stem and seed fibers in the composite
engineering. A natural fibre frequently contributes to the structural presentation of plant and
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they can deliver substantial reinforcement, when used in the production of plastics
composites.
Is curtailed to non-bearing applications because of their bring down strength
compared to synthetic fibre reinforced polymer complex in malice of the interest and
environmental appeal of natural fibers. By the sense of positioning the fibers in particular
locations for maximum strength presentation, the limitations in stiffness and strength of bio
composites can be succeeded.
Accordingly vast studies on construction and properties of polymer matrix composite
(PMC) substituting the synthetic fibre with natural fibre like Jute, Pineapple, Sisal, Kenaf,
Bamboo, luffa cylindrica, ipomea carnea and Bagasse were executed [7-12]. Above natural
fibers have numerous advantages over the glass fibre or carbon fibre such as renewable, low
cost, lightweight, high specific mechanical performance.
1.5.1 Applications
1. Automobile industry: For inner and outer parts fibre reinforced plastics are used.
These are used in industries because of their advantages over the glass fibre
reinforced composites such as cheaper, environment friendly, etc. By these fibers cars
according to End-of-Life directive can be developed as the resulting products from
these composites can be re-used and do not have to be land filled unlike glass fibre.
Because of their softness and non-harsh behaviour unlike glass fibers they are used in
interior automotive uses and are having advantages of not injuring the passengers.
2. Packaging industry: In these industries these are used for light weight pallets.
Weight reduction is the chief reason for using composite material in place of wood,
which saves fuel during transportation.
3. Consumer products: Natural fibre can be used for any injection moulded product.
Reduction of plastic use, flame retardancy and re-use. Examples are household
appliances like cell phones, refrigerators and computers. They are less vulnerable to
fire due to the fibre structure of composite. Also the high fibre loads results in major
material cost reduction.
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4. Building and construction industry: In these they are used for roofings and instance
profiles. Cost reduction, re-use and flame retardancy are the advantages.
1.5.2 Luffa cylindrica as a natural fiber
Numbers of potential natural resources are there, which India has in abundance. Most
of which comes from the forest and agriculture.
Fig 1.2 (a)
Fig 1.2 (c)
Fig 1.2 (b)
Fig 1.2 (d)
Fig. 1.2 The Luffa cylindrica plant (a), the inner fiber core (b) and the outer core open as a
mat (c, d).
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Luffa cylindrica, locally called as ‘Sponge-gourds’ is that natural resource whose
capability as fiber reinforcement in polymer composite has not been explored to date. The
fibrous cords are liable in a multidirectional array resulting in a natural mat in ligneous
netting system possess by ‘Sponge gourds’. It comprises 62% cellulose, 20% hemicellulose
and 11.2% lignin [1]. The sponge-gourd (Luffa Cylindrica) plant with fruit which belongs to
the curcubitacea family is shown in Fig. 1.1(a).
The main objective of this project is to prepare a PMC using luffa fiber as
reinforcement and epoxy as matrix material and to study its moisture absorption
characteristics under different environmental conditions and then to find its mechanical
properties i.e.; tensile and flexural strength. Out of the available manufacturing techniques,
we have chosen hand-lay-up method to construct the composite. Then the composites were
manufactured by varying the no. of layers of fiber i.e.; single, double and triple layers
composite using these techniques. The surface of fracture and worn out samples have been
studied using Scanning Electron Microscope (SEM) to have an idea about the fracture
behaviour of the composite.
In the 2nd chapter, detailed discussion on reinforcement material, outline of fabrication
processes and effort related to current investigation available in literature are presented.
In the 3rdchapter, the effect of environment on mechanical properties of both treated and
untreated fiber reinforced composite along with moisture absorption characteristics have been
presented.
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Chapter 2
LITERATURE SURVEY
Chapter-2
2.1 NATURAL FIBERS: Source and Classification
Growing environmental awareness has activated the researchers worldwide to enhance
and utilize materials that are companionable with the environment. In the procedure natural
fibers have become suitable options to traditional synthetic or manmade fibers and have the
prospective to be used in cheaper, more sustainable and more environment friendly
composite materials. Natural organic fibers can be obtained from either animal or plant
sources. Most of the useful natural textile fibers are obtained from plant, with the anomaly of
wool and silk. All plant fibers comprises of cellulose, whereas protein act as a chief content
of fibers of animal origin. Hence, the natural fibers are categorized on the basis of their
origin, whereas the plant fibers can be further classified on the basis of plant parts from
which the parts are originated. An overview of natural fibers is showed in Figure-2.1 [13].
Normally, plant or vegetable fibers are cast to reinforce polymer matrices and a
categorization of vegetable fibers is given in Figure-2.1 [14]. Plant fibers are a renewable
resource and have the capability to be recycled. The plant fibers leave slight residue if they
are burned for disposal, returning less carbon dioxide (CO2) to the atmosphere than is
separated during the plant’s growth.
The chief driver for switching natural fibers for glass is that they can be grown with
lesser cost than glass. The price of glass fiber is around Rs. 300.0/- per kg and has a density
of 2.5 gm/cc. On the other hand, natural fiber costs Rs. 15.0/- to 25.0/- per kg and has a
density of 1.2-1.5 gm/cc. As can be seen from Table-2.1 [13], although the modulus is of the
same order of magnitude, the tensile strength of natural fibre is considerably lower than the
glass fibers. On the other hand, when the specific modulus of natural fibers is measured, the
natural fibers show values that are similar to or even better than glass fibers. Material cost
savings, suitable to the use of natural fibers and high fiber filling levels, coupled with the
benefit of being non-abrasive to the mixing and moulding tools make natural fibers a thrilling
outlook. These reimbursement mean natural fibers could be used in many applications,
including building, automotive, household appliances, and several other applications.
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Table-2.1
Mechanical
Fibers
Properties
E-glass
Density (gm/cc)
Tensile
Hemp
Flax
Jute
Sisal
Coir
Ramie
2.25
1.48
1.4
1.46
1.33
1.25
1.5
Strength 2400
550-
800-1500
400-800
600-
220
500
(MPa)
Young’s
Properties of glass and natural fibers
900
Modulus 73
70
700
60-80
10-30
38
6
44
26-46
7-21
29
5
2
1.6
1.2-1.6
1.8
2-3
15-25
2
8
7
12
11
10
12-17
(MPa)
Specific
Modulus 29
(MPa)
-
Failure Strain (%)
3
Moisture
Absorption (%)
-
Natural plant fibre
Non-wood natural fibres
Straw
fibres
Bast
fibre
Wood fibres
Leaf
fibers
Seed/Fruit
fibres
fibers
fibers
Corn
Wheat
Rice
Hemp
Flax
Jute
Kenaf
Ramie
Grass
fibre
Soft wood
Hardwood
Cotton
Coir
Sisal
Henequen
Pineapple
Bamboo
Switch grass
Miscanthus
Wheat
Rice
Figure-2.1 Classification of natural fiber that can be used as reinforcements.
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2.2 CHEMICAL COMPOSITION OF NATURAL FIBERS
The component of any natural fiber differs with variety, area of production and origin,
maturation of plant. The major component of a fully developed natural fiber cell walls are
cellulose, hemicellulose, lignin and pectin. These –OH including polymers are distributed all
the way through the fibre wall [15].
2.2.1 Cellulose
The long thin crystalline micro-fibrils in the secondary cell wall are prepared of
cellulose. It is the reinforcing material and is in charge for better mechanical strength of
fibers. Chemically, cellulose is explained as a highly crystalline section alternating with
regions of non-crystalline or amorphous cellulose [16, 17].
The glucose monomers in cellulose form hydrogen bonds both inside its own chain
(intramolecular) forming fibrils and with neighbouring chains (intermolecular), creating
micro-fibrils. These hydrogen bonds lead to development of a linear crystalline structure with
high rigidity and strength. The amorphous cellulose sections have a lower frequency of
intermolecular hydrogen bonding, thus revealing reactive intermolecular -OH groups to be
bonded with water molecules. Amorphous cellulose have tendency to bond with water hence
they are considered as hydrophilic in nature. On the contrary, crystalline cellulose possess
very low accessible intermolecular –OH and thus it possess far smaller amount hydrophilicity
than the amorphous cellulose. Crystalline micro-fibrils have accessible –OH available on the
surface of the structure and also have closely filled cellulose chains in the fibrils. Only
extremely strong acids and alkalis may go through and transform the crystalline lattice of
cellulose.
2.2.2 Hemicelluloses
Hemicelluloses vary from cellulose in three dissimilar ways.
1. In contrast with cellulose (including 1,4-β-D-glucopyranose units only) they
have some assorted sugar units.
2. They reveal a considerable degree of chain branching, while cellulose is a
linear polymer.
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3. The standard of polymerization of local cellulose is ten to hundred times
greater than the hemicelluloses.
The element of hemicelluloses differs from plant to plant unlike cellulose. It includes
substituent like -COCH3 groups and glucoronic acid.
Chiefly the acid residue close to hemicelluloses makes it highly hydrophilic and raises
the fiber water uptake, which increases the danger of microbiological fiber deprivation. It has
been found that at lower temperatures hemicelluloses thermally degrade more (150-180°C)
than cellulose (200-230°C) [18].
2.2.3 Lignin
Collectively with cellulose, it is the superabundant and significant polymeric organic
substance in the world of plant. For trees of 100 meters height to stay upright lignin plays a
major role as it multiplies the compression strength of plant fibers by sticking the fibers
collectively to form a stiff structure. Lignin is basically a chaotic, polyaromatic, and crosslinked polymer emerging from the free radical polymerizations of two or three monomers
structurally associated to phenyl-propane [19]. The lignin matrix is consequently similar to a
thermoset polymer in conservative polymer terminology. The disbanding of lignin using
chemicals aids fiber separation. When reveal to ultraviolet light, lignin undergoes
photochemical deprivation. The lignin seems to perform like a matrix material contained by
the fibers, making stress transfer on a micro-fibril scale and single fiber scale achievable.
2.2.4 Pectin
Pectin, otherwise called pectic polysaccharides, is rich in galacturonic acid. A few
different polysaccharides have been distinguished and described inside the pectic gathering.
Homogalacturonans are direct chains of α-(1–4)-joined D-galacturonic acid.
Pectin is a confounded stretched structure of acidic structural polysaccharides,
established in fruits and bast fibers. Of all the compound in plant fibres pectin is the most
hydrophilic in nature as it contains carboxylic acid groups and is basically debased by
defibration with organisms [16]. Pectin together with hemicelluloses and lignin existing in
natural fibres can be hydrolysed at elevated temperatures.
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Table- 2.2Comparison between Natural Fibre and Glass Fibre
Natural Fibre
Glass Fibre
Density
Low
Twice that of Natural fibre
Cost
Low
Low, but higher than Natural
fibre
Renewability
Yes
No
Recyclability
Yes
No
Energy Consumption
Low
High
Distribution
Wide
Wide
CO2 neutral
Yes
No
Abrasion to Machining
No
Yes
Health risk when inhaled
No
Yes
Disposal
Biodegradable
Not Biodegradable
2.3 MATRIX MATERIAL
High strength properties are shown by various materials only when they are in fibrous
form and these properties are attained if the fibre is bonded by an appropriate matrix. Matrix
segregates the fibers from each other so as to avoid abrasion and establishment of fresh
surface defect and behave as a link to grip the fibres in a particular position. Under applied
load, matrix tends to possess the capability to deform quite easily, uniformly distribute
concentrated stress and transfers the load to the fibers effectively but in order to get these the
matrix should be of good quality.
A study of the nature of bonding forces in laminates [20] specifies that upon initial
loading there is an affinity for the adhesive bond into them to report for the high strength
properties of the of the laminates.
In order to transfer the load to the fibers through matrix and to guard them from
handling and environments the polymer matrix should sticks the fibers together. Polymer or
resin systems are used to manufacture advanced Polymer Matrix Composites (PMCs) is of
two primary types, thermosets and thermoplastics.
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2.3.1 Thermosets
Much of the initial work used thermosetting resins as matrix material for composite
construction. Products like tufnol which is shaped using cotton fibres and epoxy resin, have
been available for some time, possessing good stiffness and strength [21]. In the past few
years there has been transformed interest in these products for use in automotive applications.
To attain reinforcing consequences in composites it is essential to have decent adhesion
across the resins and fiber. Epoxy and phenolic thermosetting resins are well-known to be
capable to form covalent cross-links with plant cell walls along -OH groups. Production of
composite can be achieved by means of low viscosity epoxy and phenolic resins that cure at
room temperature. In accumulation epoxy resin does not yield volatile products throughout
curing which is most advisable in construction of void free composites. Although epoxy
resins are comparatively more expensive than polyester, they possess high potential for the
development of added value plant fiber composites, whereas long fibres at a high content are
mandatory.
Figure-2.2
Chemical structure of DGEBA
For curing agents of epoxy resins primary and secondary amines are mainly used. On
the whole, reaction rate of an amine with an epoxide is dominated by the steric encumbrance
and the electron donating groups that exists in the amine.
The merits of epoxy resins are low polymerisation shrinkages unlike polyesters during
cure, excellent resistance to chemicals and solvents, good mechanical strength, and excellent
adhesion to fibres. The epoxy molecule consist of two ring groups at its centre, that have the
capability to absorb both thermal and mechanical stresses better than the linear groups, giving
epoxy resin very good strength, toughness, stiffness and heat resistance.
The main demerits of the epoxy resins are that they need long curing times and, for
the most part, their mould discharge qualities are poor. The epoxy resins are categorized by
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high adhesive strengths. After reviewing the stimulating literature accessible on the natural
fiber composite hard work are put to recognise the basic needs of the emerging composite
industry. The decisions drawn from this is that, the achievement of merging vegetable natural
fibers with polymer matrices results in the improvement of mechanical properties of the
composite associated with the matrix material. These fillers are cheap and non-toxic and can
be acquire from renewable source and are effortlessly recyclable. Furthermore in spite of
their low strength, they may results into composite possessing high specific strength due to
their low density.
Thus significance of this work is to prepare polymer matrix composites (PMCs) using
Luff Cylindrica fiber as reinforcement material. To increase the interfacial strength among
the fibre and the matrix, the surface alteration of the fibre has to be done by chemical
treatment. The composite is then being subjected to different environmental conditions like
saline and distil condition. The mechanical properties of the composite will be estimated
along with moisture absorption characteristics.
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Chapter 3
MECHANICAL CHARACTERIZATION
OF LUFFA CYLINDRICA FIBRE EPOXY
COMPOSITE
Chapter-3
3.1INTRODUCTION
In common natural fibers are absorptive in nature and they take up or liberate
moisture relying on to the environmental conditions. For high moisture absorption rate
amorphous cellulose and hemicellulose present in the fibre are the main reasons, as they
possess innumerable easily available -OH groups which provide an increased level of
hydrophilic property to the fibre. The high moisture absorption of the fiber happens due to
hydrogen bonding of water molecules to the -OH groups in the fiber cell wall. This guides to
a moisture growth in the fibre cell wall (fibre swelling) and also in the fibre-matrix border.
This in turn becomes liable for variations in the dimensions of cellulose-based composites,
mainly in the thickness and the linear expansion because of reversible and irreversible
swelling of the composites. In order to solve this problem, chemical treatment has been taken
into account as a good method to reduce the -OH group in the fibers. Different chemical
treatments such as alkali treatment, acrylation, benzoylation, isocyanate treatment, acetone
treatment, acetylation, silane treatment, permanganate treatment etc. are reported by many
researchers [22, 23].
The moisture uptake of composites comprising natural fibers has some unfavourable
causes on their properties and hence disturbs their long-term presentation. In view of the
sternness of moisture absorption and its consequences on composite properties, a number of
efforts have already been made by several researchers to address this issue.
Jena et al. [24] studied the water absorption behaviour of bamboo-epoxy composite filled
with cenosphere. Water absorption of bamboo fibre increases with time of immersion,
attaining a saturation point after which it remains constant. She observed that the saturation
point was different for two different environmental conditions. For distilled water it was 216
h whereas for saline water it was 168 h.
Joseph et al. [25] investigated the environmental effects on sisal fibre reinforced PP
composites. Absorption of water was found to be increased with the fibre content and then
settled off at longer period of time. In order to overcome this problem the fibres were treated
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chemically and the chemically treated fibres showed a decrease in water absorption because
of the enhanced interfacial bonding. As the temperature stimulates the diffusion procedure, it
was found that the water absorption of the composite increases with the temperature.
Plasticization effect of water was the reason to decrease the tensile properties of the
composites.
Yuan et al. [26] experimented the plasma treatment of sisal fibers and its possessions on
tensile strength and interfacial bonding. They recommended that cleaned and chemically
customized fiber surface improves the interfacial adhesion among the fibre and matrix. The
rate of moisture absorption in bio-composite was reduced by the strong intermolecular
bonding among fiber and matrix.
Stamboulis et al. [27] reported that the swelling and moisture absorption of the treated
flax fibre polypropylene composites is lower than the untreated flax fibers composites. The
result shows that the absorption for the treated fibre is approximately 30% lower than the
untreated fibre composites.
Thomas et al. [28], while experimenting water absorption characteristics of sisal fiber
polyester composites established that the diffusion coefficient decreases with chemical
treatment of fiber. In addition to this the chemical treatment also reduces water absorption
capacity of the composite. They also showed that the composite with benzoyl-chloride treated
sisal fiber composite exhibited lower water absorption capacity.
Satyanarayana et al. [29] have investigated on lignocellulosic fibers of Brazil. They
reported the accessibility to some of the Brazilian lignocellulosic fibers, extraction methods,
properties, their market and their applications. International trends in the study of
lignocellulosic fibers tells that, these fibers have dormant use in automotive applications; they
can be perfect competitors for the non-renewable, costly petroleum-based synthetic fibers in
composite materials, mostly in the automotive industry and counting building sectors.
Andrzej et al. [30] have studied the impact of the type of reinforcing fibre, fibre and void
content on the mechanical properties of composites. Increase in the shear modulus and impact
strength was influenced by increasing the content of the fibre. There is decrease in impact
strength and shear modulus due to increase in micro void content.
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Verma et al. [31] have examined the usage of bagasse fiber and its current calibre of
research. Many citations to the latest work on processing, application and properties have
been quoted in this assessment. The main aim of their study was to employ the benefits
provided by renewable resources for the development of composite materials based on
bagasse fibers. They determined that the natural fibre composites can be more suitable for
technical applications such as automotive interior parts when they are hybrid with certain
quantity of synthetic fibre.
Herrera-Franco et al. [32] have investigated the mechanical performance of high density
polyethylene (HDPE), strengthened with continuous henequen fibers. They established that
the strength and toughness of the composite depends on the quantity of silane settled down on
the fiber and with the surface alteration there is no enhancement in the elastic modulus of the
composite.
Oboh et al. [33] have reported the potentialities of Luffa cylindrica crop that is virtually
found around the world. Regions such as medicine, agriculture, science, biotechnology and
engineering were discussed. Recent major improvements and discoveries were considered.
They conclude that in the context of the morphosynthesis, the capability of replication of the
luffa sponge unties the chances of the use of biodiversity in obtaining new materials. This
emerging cash crop will expand the economies of many nations in the nearest future because
of its numerous potentials.
Yoldas Seki et al. [34] carried out report of Luffa cylindrica by scanning electron
microscopy (SEM) analysis. The contents of hemicellulose, lignin and cellulose in Luffa
cylindrica were determined. They subject luffa cylindrica-reinforced polyester composite to
water aging in a steam of seawater containing 5% NaCl for 170 hrs at 500C. They found that
flexural strength, tensile strength, tensile elongation and interlaminar shear strength at break
values was decreased by 28%, 24%, 45%, and 31%, respectively, after the process of aging.
Msahli et al.
[35] have reported the influence of fiber weight ratio ,reinforcement
structure and chemical modification on the flexural proprieties of Luffa-polyester composites.
It resorts that acetylating and cyanoethylating improve the flexural strength and the flexural
modulus. They established that the fiber weight ratio influenced the flexural properties of
composites. Positively, a maximum value of strength and strain is observed over a 10% fiber
weight ratio. They examined the uses of various reinforcement structures.
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3.2 CHEMICAL MODIFICATION OF FIBER
Utilizing natural fibers as reinforcement in the organization of plastic composites has
improved intensely in recent years. For a well-developed composite using natural fibre as
reinforcement the understanding of surface adhesive bonding of fibre and the chemical
composition is essential. Interfacial bonding between fibers and the resin needs to be good as
it plays a significant role in enhancing the mechanical properties of the composites.
Understanding the importance of chemically modified fibers, numerous authors have started
studying treatment of fibers in order to develop the bonding with resin matrix. The quantity
of individual material in a composite and the nature of interfacial region between matrix and
reinforcement decides the mechanical properties of the composites.
Absence of good interfacial adhesion makes the usage of cellular fiber composites less
attractive. Frequently, due to water absorbing nature of natural fibre the interfacial properties
between the fiber and polymer matrix tends to be low, which decreases its potential of being
used as reinforcing agents. Hence chemical alterations are taken into account to enhance the
interface of fibers. There are several chemical treatments that exist for the fibre surface
modification. Chemical treatment comprising alkali, silane, acetylation, benzoylation,
acrylation, isocynates, maleated coupling agents, permanganate treatment are discussed in
details in.
The main reason for performing chemical alterations on natural fibres is to improve the
adhesion between fibre surface and the polymer matrix by altering the fibre surface and the
fibre strength. It also helps in enhancing the mechanical properties by decreasing the water
absorption capability of the fibre. Out of the available treatments, for the present case to have
a decent bonding between the fibre and the matrix Luffa Cylindrica fibre have been treated
with alkali. The subsequent section will elaborate separately the treatment of the fibre surface
by alkali methods, study of mechanical properties of both treated and untreated fibre
reinforced polymer composite followed by studying environmental effects on mechanical
performance of the composite along with moisture absorption characteristics.
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3.2.1
Method of Chemical Modification
3.2.1.1 Alkaline Treatment
When it comes to reinforce thermoplastics and thermosets, alkaline treatment is one
of the mostly used treatments. In the modification done by the alkaline treatment the
disruption of hydrogen bonding in the network structure takes place resulting in increased
surface roughness. By using this treatment, certain amount of lignin, wax and oils covering
the outer surface wall of the fibre was removed, depolymerizes cellulose and depicts the
short length crystallites [36]. Addition of aqueous sodium hydroxide (NaOH) to natural fibre
stimulates the ionization of the -OH group to the alkoxide.
Fiber –OH + NaOH → Fiber – O – Na +H2O
Alkaline treatment has two effects on the fibre:
1) It increases surface roughness by the disruption of hydrogen bonding resulting in
better mechanical linking, and
2) It increases the number of possible reactions sites by increasing the amount of
cellulose exposed on the fibre surface.
Subsequently, this treatment has a lasting effect on the mechanical behaviour of flax
fibre, especially on the strength and stiffness of the fibre.
For performing this treatment, Firstly the Luffa Cylindrica fibre were kept in a solution
containing 5%NaOH at room temperature maintaining a liquor ration of 15:1 for 4hrs.
Secondly, the fibers were washed many times with water in order to remove the NaOH
sticking to the fibre surface followed by neutralizing with dilute acetic acid and washed with
distilled water, so that pH of 7 was maintained. Lastly, the fibers were dried at room
temperature for 48hrs followed by oven drying for 6hrs at 100ºC. The alkali reaction between
Luffa Cylindrica fibre and NaOH is as follows:
(Luffa Cylindrica) – OH + NaOH ↔ (Luffa Cylindrica) – O-Na+ + H2O
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3.3 COMPOSITE FABRICATION
For preparation of composite the following materials have been used;
1.
Luffa Cylindrica fiber
2.
Epoxy
3.
Hardener
3.3.1 Preparation of Luffa Cylindrica Fiber Mats
Dried Luffa Cylindrica was collected locally. These fibres were then treated with
water for 24 hrs in order to remove wax, lignin and oil from the external surface of luffa fibre
and then dried at room temperature. After these the fibres were cut with appropriate
dimensions (150×140 mm) and then these fibres were kept between two wooden boards
followed by pressing it into the bench vice to straighten the fibres.
3.3.2 Epoxy Resin
The epoxy resin used in this examination is Araldite LY-556 which chemically
belongs to epoxide family. Its common name is Bisphinol-A-Diglycidyl-Ether. The hardener
with IUPAC name NNO-bis (2aminoethylethane-1,2diamin) has been used with the epoxy
designated as HY 951.
3.3.3 Composite preparation
Initially, wooden moulds with dimensions of 140 x 120 × 10 mm3 were prepared for
the fabrication. For different number a layer of fibre, epoxy resin and hardener (ratio of 10:1
by weight) with a calculated amount was mixed thoroughly in a glass jar. Figure 3.1(a)
illustrates the mould used to construct the composite. Mould release sheet was put over the
glass plate and a mould release spray was sprayed over the inner surface of the mould for
quick and easy removal of composite. After keeping the mould on a ply board a thin layer of
the mixture was poured. Then the fiber lamina was distributed on the mixture. Then again
resin was applied over the fiber laminate and the procedure was repeated to get the desired
thickness. The remaining mixture was then poured into the mould. Precaution was taken to
prevent the air bubbles formation. Then from the top pressure was applied and the mould was
kept at room temperature for 72 hrs. During application of pressure some amount of mixture
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of epoxy and hardener squeezes out. Care has been taken to consider this loss during
manufacturing of composite sheets. After 72 hrs the samples were taken out of the mould.
Figure 3.2 (a, b) shows the photograph of the composite specimen cut for further
experimentation.
Figure- 3.1 Mould used for fabrication of the composite
Figure-3.2 (a) Flexural test samples
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Figure-3.2 (b) Tensile test samples
3.4. STUDY OF ENVIRONMENTAL EFFECT
To study the effect of environmental conditions on performance of Luffa Cylindrica
fiber epoxy composite, the composite sample with both untreated and chemically treated
fibers were subjected to various environments such as:
(a) Saline treatment
(b) Distil treatment
3.4.1 Moisture absorption test
Moisture absorption and thickness swelling tests were conducted in accordance with
ASTM D570-98. Four specimens for different layers (Single, Double and Triple layers) were
cut with dimensions of 140 x 15mm (length x width) and the experiment was performed
using test samples. The specimens prior to testing were dried in an oven at 800 C and then
were allowed to cool to room temperature and kept in a desiccator. The weight of the samples
were taken before subjected to steam, saline water and distil water environments. After
expose for 12 hr, the specimens were taken out from the moist environment and all surface
moisture was removed with a clean dry cloth or tissue paper. The specimens were reweighed
to the nearest 0.001 mg within 1 min. of removing them from the environment chamber. The
specimens were weighed regularly from 12-156 hrs with a gap of 12hrs of exposure. The
moisture absorption was calculated by the weight difference. The percentage weight gain of
the samples was measured at different time intervals by using the following equation:
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%Mt 
Wt  W0  100
W0
(3.1)
Where ‘W0’ and ‘Wt’ denote the oven-dry weight and weight after time ‘t’, respectively.
Equilibrium Moisture Content (EMC) of the sample is the moisture content when the periodic
weight change of the sample was less than 0.1% and thus the equilibrium state was assumed
to be reached.
The thickness swelling (TS) was determined by using the following equation:
TS(t) 
H t  H0
 100
H0
(3.2)
Where, ‘Ht’ and ‘H0’ are the composite thickness after and before the water immersion
respectively.
3.4.2 Mechanical testing of sample
3.4.2.1 Tensile test
The tensile test is generally performed on flat specimens. The most commonly used
specimen geometries are dog-bone and the straight side type with end tabs. The specimen
used in present case is shown in fig 3.3 (a). The tensile tests were conducted according to
ASTM D 3039-76 standard on a computerized Universal Testing Machine INSTRON
H10KS. The span length of the specimen was 42 mm. the tests were performed with constant
strain rate of 2 mm/min.
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Figure-3.4 (a) UTM machine sample unloaded for tensile testing
Figure 3.4 (b) UTM machine sample loaded for tensile testing
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3.4.2.2 Flexural test
Three point bend test was carried out in an UTM machine in accordance with
ASTM D790-03 to measure the flexural strength of the composites. The loading arrangement
for the specimen and the photograph of the machine used are shown in figure 3.5. All the
specimens (composites) were of rectangular shape having length varied from 100-125 mm,
breadth of 100-110 mm and thickness of 4-8 mm. A span of 70 mm was employed
maintaining a cross head speed of 0.5mm/min.
The flexural strength of composites was found out using the following equation
τ=
Where τ is the flexural strength, f is the load, l is the gauge length, b is the width and t
is the thickness of the specimen under test.
Figure 3.5 UTM machine sample unloaded for flexural testing
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3.4.3
Results and discussion
3.4.3.1 Moisture absorption behaviour
The results of both untreated and treated fibre composite samples exposed to different
environments are shown in Table-3.1 to 3.24.
Figure-3.22 to 3.29 shows the percentage of moisture absorption characteristics of
composite samples with untreated and treated fiber exposed to Saline water and Distil
environment with time. It is quite obvious from the figure that as the fibre content increases,
the initial rate of moisture absorption and the maximum moisture absorption for both the
environment increases. Moisture absorption is maximum for three layered composites. It is
known that, the factors like adhesion between fibre and matrix, porosity content and the
lumen are responsible for the moisture absorption behaviour of the natural fibre composites.
But in this case the hydrophilicity of Luffa Cylindrica fiber, in addition to poor adhesion
between fiber–matrix and voids content might have affect the moisture uptake characteristics
of the composite.
Again it is observed that, the moisture absorption increases as the immersion time
increases, and got saturated after certain time period. Time required to reach the saturation
point is not same for both the environments. The saturation time is approximately 120 hrs for
distil, and 108 hrs for saline water. Environmental conditions also play a significant role in
moisture absorption process. Figure-3.30 to 3.33 shows the maximum moisture absorption of
composite in all three environments. In Distil Water environment moisture absorption is
maximum as compare to saline water environment. The rate of absorption in case of saline
water is low as compared to steam. This happens because of the gathering of NaCl ions in the
fibre’s surface immersed in saline water, which increases with time and delays moisture
diffusion [122].
Figure-3.22 to 3.29 shows that the moisture absorption behaviour of the chemically
treated fibre reinforced epoxy composites was lesser than that of the untreated fibre when
exposed to different environmental treatment. It is clear from these plots that the change in
surface chemistry of the fibre reduces the attraction of fibers to moisture. Due to surface
modification by chemical treatment, the fibers get covered with the epoxy resin with a
stronger adhesion, resulting in less moisture uptake.
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3.4.3.2 Measurement of Diffusivity
The water sorption kinetics in LCF reinforced epoxy composite has been studied
through the diffusion constants k and n. The behaviour of moisture sorption in the composite
was studied by the shape of the curve represented by the equation (3.3) [37, 38]:
M
M
t
 kt n
(3.3)
m
Where, Mt is the moisture content at specific time‘t’,
Mm is the equilibrium moisture content (EMC), and
k and n are constants.
The value of k and n were found out from the slope and the intercept of M t /Mm
versus time ‘t’ in the log plot which was drawn from the data obtained from experiment of
moisture absorption with time.Figure-3.14 to 3.16 and Figure-3.17 to 3.19 showed the typical
curve of log (Mt/Mm) as a function of log (t) for both untreated and treated LCF reinforced
epoxy composite respectively, used to determine these constants. The values of k and n
resulting from the fitting of all formulations are shown in Table-3.25 and 3.26. It was
observed that the value of n is close to 0.9 for all of the composites. This confirms that the
Fickian diffusion can be used to adequately describe moisture absorption in the composites.
A higher value of n and k indicates that the composite needs shorter time to attain equilibrium
water absorption. The value of k was found to increases with increasing fibre content for LCF
reinforced epoxy composite in all environments resulting higher moisture absorption initially.
The value of k for untreated fiber composite was higher than that of treated fiber composite,
except saline water environment. It might have happened due to the gathering of NaCl ions in
the fiber’s surface which delays subsequent moisture diffusion.
The diffusion coefficient or diffusivity (Dx) of moisture absorption was calculated
using the following equation:
NIT ROURKELA
Page 33
 h   M 2  M 1 
Dx  π 

 4M m   t 2  t 1 
2
2
(3.4)
where ‘Mm’ is the maximum percentage of moisture content, ‘h’ is the sample
thickness, ‘t1’ and ‘t2’ are the selected points in the initial linear portion of the plot of
moisture absorption (Mt) versus t (Figure-3.21) and ‘M1’ and ‘M2’ are the respective
moisture content.
From the plot of Mt verses square root of time (t) the value of Dx has been evaluated and
summarized in Table-3.27 and 3.28. It has been observed Dx value increases with the LCF
content for the composites examined. These results are consistent with previous findings on
wood and natural fibers composites. The increase was more pronounced for the specimens
subjected to steam than those subjected to saline water and sub-zero environments. The
surface modification of fiber decreases the diffusion coefficient (Dx).
3.4.4 Effect of moisture absorption on Mechanical properties
The mechanical properties of the natural fibre polymer composite were greatly
influenced by the moisture absorption. Figure-3.6 to3.13 shows the result of mechanical
properties of the composite with both treated and untreated fibre reinforced composite after
expose to different environment for a period of 156 hrs. It has been observed that, both
strength and stiffness of all composite decrease after moisture absorption. This reduction in
the stiffness and strength is accredited to the changes occurring in the fibre, and the interface
between fibre and matrix. When fibre/matrix interface is exposed to moisture from the
environment, the cellulosic fibers tend to swell, thereby developing shear stresses at the
interface, which favours ultimate debonding of the fibers, which in turn causes strength
reduction [85]. It is also observed that the reduction in properties was greatly influenced by
the fibre loading and nature of environment. The maximum reduction in strength and stiffness
occured in case of three layered composite in both the environments. Further it is also noticed
that the amount of decrease in mechanical properties is reduced with chemical modification
of fibre. The alkali treated fibre composite exhibits the best result in both the environments in
NIT ROURKELA
Page 34
comparison to other untreated fibre composite. Because the alkali treatment reduces the
hydrophilic nature of the fibre to great extend which leads to less moisture absorption.
3.4 CONCLUSIONS
Based on experimental results, this study has led to the following conclusions:

The Luffa Cylindricafibre can successfully be used as reinforcing agent to fabricate
composite by suitably bonding with epoxy resin. .

On increasing the fibre content the strength, modulus and work of fracture increases
and the best combination is found with Double Layered composite.

The fibre surface modification by chemical treatments significantly improves the fibre
matrix adhesion, which in turn improves the mechanical properties of composite.

The moisture uptake and thickness swelling values increases with increase in fiber
loading. Both values are found to be higher in saline environment than in distil water
environments. However these values are considerably reduced with chemical
treatments of the fibre.

Under all environment conditions, the moisture diffusion process of both treated and
untreated Luffa Cylindricafibre composites are found to follow the Fick’s law.

Fibre breakages are found to be the predominant mode of failure as ascertained from
the morphology of the treated fibre composites.
NIT ROURKELA
Page 35
Table–3.1. Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil
environment.
No. of
Immersion
Weight of
Percentage of
Thickness
Thickness
layers
Time ‘t’
the
weight gain
at time ‘t’
Swelling
(hrs)
Sample
(%M)
H(t)
TS (t)
0
12.761
0
0.59
0
12
12.986
1.763184703
0.591
0.169491525
24
13.038
2.170676279
0.592
0.338983051
36
13.063
2.366585691
0.593
0.508474576
48
13.136
2.938641172
0.594
0.677966102
60
13.213
3.54204216
0.595
0.847457627
72
13.228
3.659587807
0.596
1.016949153
84
13.253
3.855497218
0.597
1.186440678
96
13.283
4.090588512
0.598
1.355932203
108
13.486
5.681372933
0.599
1.525423729
120
13.598
6.559047097
0.6
1.694915254
132
13.598
6.559047097
0.6
1.694915254
144
13.598
6.559047097
0.6
1.694915254
156
13.599
6.566883473
0.6
1.694915254
Single
Layer
NIT ROURKELA
Page 36
Table–3.2 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil environment.
No. of
Immersion
Weight of
Percentage of
Thickness
Thickness
layers
Time ‘t’
the
weight gain
at time ‘t’
Swelling
(hrs)
Sample
(%M)
H(t)
TS (t)
0
15.504
0
0.707
0
12
15.954
2.90247678
0.709
0.282885431
24
16.123
3.99251806
0.71
0.424328147
36
16.421
5.914602683
0.713
0.848656294
48
16.652
7.404540764
0.715
1.131541726
60
16.669
7.514189886
0.717
1.414427157
72
16.701
7.720588235
0.719
1.697312588
84
16.821
8.494582043
0.721
1.98019802
96
17.015
9.745872033
0.723
2.263083451
108
17.125
10.45536636
0.725
2.545968883
120
17.131
10.49406605
0.726
2.687411598
132
17.131
10.49406605
0.726
2.687411598
144
17.132
10.500516
0.726
2.687411598
156
17.132
10.500516
0.726
2.687411598
Double
Layer
Sample 3
NIT ROURKELA
Page 37
Table–3.3 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil environment.
No. of
Immersion
Weight of
Percentage of
Thickness at
Thickness
layers
Time ‘t’
the
weight gain
time ‘t’
Swelling
(hrs)
Samples
(%M)
H(t)
TS (t)
0
16.974
0
1.125
0
12
18.166
7.02250501
1.128
0.266666667
24
18.414
8.4835631
1.132
0.622222222
36
18.831
10.9402616
1.136
0.977777778
48
19.162
12.8903028
1.14
1.333333333
60
19.284
13.6090491
1.143
1.6
72
19.373
14.1333805
1.147
1.955555556
84
19.622
15.6003299
1.15
2.222222222
96
19.726
16.2130317
1.154
2.577777778
108
19.767
16.4545776
1.158
2.933333333
120
19.921
17.3618475
1.162
3.288888889
132
20.11
18.4753152
1.162
3.288888889
144
20.112
18.4870979
1.162
3.288888889
156
20.112
18.4870979
1.162
3.288888889
Triple
Layer
Sample 5
NIT ROURKELA
Page 38
Table–3.4 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at distil environment.
No. of layers
Immersion
Weight
Percentage of
Thickness
Thickness
Time ‘t’
of the
weight gain
At time ‘t’
Swelling
(hrs)
sample
(%M)
H(t)
TS (t)
0
11.801
0
0.637
0
12
12.124
2.737056182
0.638
0.156985871
24
12.234
3.669180578
0.639
0.313971743
36
12.342
4.584357258
0.64
0.470957614
48
12.410
5.160579612
0.641
0.627943485
60
12.564
6.465553767
0.642
0.784929356
72
12.671
7.372256588
0.643
0.941915228
84
12.784
8.329802559
0.644
1.098901099
96
12.897
9.28734853
0.645
1.25588697
108
12.994
10.10931277
0.646
1.412872841
120
12.994
10.10931277
0.647
1.569858713
132
12.994
10.10931277
0.647
1.569858713
144
12.994
10.10931277
0.647
1.569858713
156
12.994
10.10931277
0.647
1.569858713
Single Layer
NIT ROURKELA
Page 39
Table–3.5 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at distil environment.
No. of
layers
Immersion
Time ‘t’
(hrs)
Weight
of the
Sample
Percentage of
weight gain
(%M)
Thickness at
time ‘t’
H(t)
Thickness
Swelling
TS (t)
0
13.602
0
0.713
0
12
13.847
1.80120571
0.715
0.280504909
24
14.145
3.99205999
0.717
0.561009818
36
14.354
5.52859874
0.719
0.841514727
48
14.557
7.02102632
0.721
1.122019635
60
14.743
8.38847228
0.723
1.402524544
72
14.957
9.96177033
0.725
1.683029453
84
15.147
11.3586237
0.727
1.963534362
96
15.354
12.8804588
0.729
2.244039271
108
15.145
13.6965152
0.731
2.52454418
120
15.465
13.6965152
0.733
2.805049088
132
15.465
0.733
2.805049088
144
15.465
13.6965152
0.733
2.805049088
156
15.465
13.6965152
0.733
2.805049088
Double
Layer
NIT ROURKELA
13.6965152
Page 40
Table–3.6 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at distil environment.
No. of
layers
Triple
Layer
Sample 3
NIT ROURKELA
Immersion
Time ‘t’
(hrs)
Weight of
the
Sample
Percentage of
weight gain
(%M)
Thickness at
time ‘t’
H(t)
Thickness
Swelling
TS (t)
0
14.688
0
1.125
0
12
15.128
2.9956427
1.129
0.355555556
24
15.547
5.84831155
1.134
0.8
36
15.947
8.57162309
1.137
1.066666667
48
16.374
11.4787582
1.141
1.422222222
60
16.654
13.3850763
1.144
1.688888889
72
16.957
15.4479847
1.147
1.955555556
84
17.324
17.9466231
1.15
2.222222222
96
17.674
20.3295207
1.154
2.577777778
108
18.957
22.2562636
1.158
2.933333333
120
18.957
22.2562636
1.162
3.288888889
132
18.957
22.2562636
1.162
3.288888889
144
18.957
22.2562636
1.162
3.288888889
156
18.957
22.2562636
1.162
3.288888889
Page 41
Table–3.7 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil environment.
No. of
Time of
layers
immersion
Single
layer
0
14.138
0
0.617
0
12
14.235
0.686094214
0.618
0.162074554
24
14.358
1.55608997
0.619
0.324149109
36
14.487
2.468524544
0.62
0.486223663
48
14.541
2.8504739
0.621
0.648298217
60
14.635
3.515348706
0.622
0.810372771
72
14.741
4.265101146
0.623
0.972447326
84
14.852
5.050219267
0.624
1.13452188
96
14.957
5.792898571
0.625
1.296596434
108
14.972
5.898995615
0.626
1.458670989
120
14.972
5.898995615
0.626
1.458670989
132
14.972
5.898995615
0.626
1.458670989
144
14.972
5.898995615
0.626
1.458670989
156
14.972
5.898995615
0.626
1.458670989
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 42
Table–3.8 Variation of weight gain and thickness swelling of untreated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil environment.
No. of
Time of
Final
layers
immersion
Wt.
Double
layer
0
12.367
0
0.499
0
12
12.523
1.261421525
0.501
0.400801603
24
12.745
3.056521388
0.503
0.801603206
36
12.941
4.641384329
0.505
1.20240481
48
13.102
5.943236031
0.507
1.603206413
60
13.304
7.576615186
0.509
2.004008016
72
13.516
9.290854694
0.511
2.404809619
84
13.712
10.87571764
0.513
2.805611222
96
13.923
12.58187111
0.515
3.206412826
108
14.001
13.21258187
0.517
3.607214429
120
14.001
13.21258187
0.517
3.607214429
132
14.001
13.21258187
0.517
3.607214429
144
14.001
13.21258187
0.517
3.607214429
156
14.001
13.21258187
0.517
3.607214429
NIT ROURKELA
Wt. Change
Thickness
Thickness
Swelling
Page 43
Table–3.9 Variation of weight gain and thickness swelling of untreated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at distil environment.
No. of
Time of
Final
layers
immersion
Wt.
Triple
layer
NIT ROURKELA
Wt. Change
Thickness
Thickness
Swelling
0
19.295
0
0.866
0
12
19.547
1.306037834
0.87
0.461893764
24
19.925
3.265094584
0.874
0.923787529
36
20.218
4.7836227
0.879
1.501154734
48
20.754
7.561544442
0.884
2.07852194
60
20.998
8.826120757
0.888
2.540415704
72
21.456
11.19979269
0.892
3.002309469
84
21.879
13.39207048
0.896
3.464203233
96
22.241
15.2682042
0.902
4.15704388
108
22.741
17.85954911
0.906
4.618937644
120
22.741
17.85954911
0.906
4.618937644
132
22.741
17.85954911
0.906
4.618937644
144
22.741
17.85954911
0.906
4.618937644
156
22.741
17.85954911
0.906
4.618937644
Page 44
Table–3.10 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at distil
environment.
No. of
layers
Time of
immersion
Final
Wt.
Wt. Change
Thickness
Thickness
Swelling
0
11.199
0
0.54
0
12
11.247
0.428609697
0.541
0.185185185
24
11.395
1.750156264
0.542
0.37037037
36
11.551
3.14313778
0.543
0.555555556
48
11.628
3.83069917
0.544
0.740740741
60
11.784
5.223680686
0.545
0.925925926
72
11.871
6.000535762
0.546
1.111111111
84
11.967
6.857755157
0.547
1.296296296
96
12.117
8.197160461
0.548
1.481481481
108
12.228
9.188320386
0.549
1.666666667
120
12.374
10.49200822
0.549
1.666666667
132
12.374
10.49200822
0.549
1.666666667
144
12.374
10.49200822
0.549
1.666666667
156
12.374
10.49200822
0.549
1.666666667
SL
NIT ROURKELA
Page 45
Table–3.11 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at distil
environment.
No. of
layers
Time of
immersion
Final
Wt.
Wt. Change
Thickness
Thickness
Swelling
0
11.995
0
0.591
0
12
12.108
0.942059191
0.593
0.338409475
24
12.354
2.992913714
0.595
0.676818951
36
12.546
4.593580659
0.597
1.015228426
48
12.821
6.886202584
0.599
1.353637902
60
12.983
8.236765319
0.601
1.692047377
72
13.099
9.203834931
0.603
2.030456853
84
13.212
10.14589412
0.605
2.368866328
96
13.521
12.72196749
0.607
2.707275804
108
13.715
14.33930805
0.609
3.045685279
120
13.715
14.33930805
0.609
3.045685279
132
13.715
14.33930805
0.609
3.045685279
144
13.715
14.33930805
0.609
3.045685279
156
13.715
14.33930805
0.609
3.045685279
DL
Sample 2
NIT ROURKELA
Page 46
Table–3.12 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at distil
environment.
No. of layers
Time of
Final
Wt. Change
Thickness
Thickness
immersion
Wt.
0
13.046
0
0.668
0
12
13.398
2.698145025
0.671
0.449101796
24
13.604
4.27717308
0.674
0.898203593
36
13.951
6.936992182
0.677
1.347305389
48
14.314
9.719454239
0.68
1.796407186
60
14.618
12.0496704
0.683
2.245508982
72
14.983
14.84746282
0.686
2.694610778
84
15.287
17.17767898
0.689
3.143712575
96
15.549
19.18595738
0.692
3.592814371
108
15.895
21.8381113
0.695
4.041916168
120
15.895
22.61996014
0.695
4.041916168
132
15.895
22.61996014
0.695
4.041916168
144
15.895
22.61996014
0.695
4.041916168
156
15.895
22.61996014
0.695
4.041916168
Swelling
TL
Sample 1
NIT ROURKELA
Page 47
Table–3.13 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (flexural) with immersion time expose at saline
environment.
No. of
Time of
layers
immersion
Single
Layer
0
11.836
0
0.55
0
12
12.014
1.503886448
0.551
0.181818182
24
12.18
2.906387293
0.552
0.363636364
36
12.291
3.844204123
0.553
0.545454545
48
12.368
4.494761744
0.554
0.727272727
60
12.532
5.880364988
0.555
0.909090909
72
12.741
7.646164245
0.556
1.090909091
84
12.887
8.879689084
0.557
1.272727273
96
12.913
9.099357891
0.558
1.454545455
108
12.998
9.817505914
0.559
1.636363636
120
12.998
9.817505914
0.559
1.636363636
132
12.998
9.817505914
0.559
1.636363636
144
12.998
9.817505914
0.559
1.636363636
156
12.998
9.817505914
0.559
1.636363636
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 48
Table–3.14 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at saline environment.
No. of
Time of
layers
immersion
Double
Layer
0
15.665
0
0.769
0
12
15.821
0.995850622
0.771
0.260078023
24
16.246
3.708905203
0.773
0.520156047
36
16.521
5.464411108
0.775
0.78023407
48
16.825
7.40504309
0.777
1.040312094
60
16.993
8.477497606
0.779
1.300390117
72
17.241
10.06064475
0.781
1.56046814
84
17.521
11.84806894
0.783
1.820546164
96
17.724
13.14395148
0.785
2.080624187
108
17.928
14.44621768
0.787
2.340702211
120
17.928
14.44621768
0.787
2.340702211
132
17.928
14.44621768
0.787
2.340702211
144
17.928
14.44621768
0.787
2.340702211
156
17.928
14.44621768
0.787
2.340702211
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 49
Table–3.15 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at saline environment.
No. of
Time of
layers
immersion
Triple
layer
0
17.75
0
1.113
0
12
18.324
3.233802817
1.117
0.359389039
24
18.925
6.61971831
1.121
0.718778077
36
19.363
9.087323944
1.124
0.988319856
48
19.724
11.12112676
1.128
1.347708895
60
19.947
12.37746479
1.131
1.617250674
72
20.259
14.13521127
1.135
1.976639712
84
20.624
16.1915493
1.14
2.425876011
96
20.989
18.24788732
1.145
2.875112309
108
21.112
18.94084507
1.148
3.144654088
120
21.112
18.94084507
1.148
3.144654088
132
21.112
18.94084507
1.148
3.144654088
144
21.112
18.94084507
1.148
3.144654088
156
21.112
18.94084507
1.148
3.144654088
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 50
Table–3.16 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at saline
environment.
No. of
Time of
Initial
Final
layers
immersion
Wt.
Wt.
Single
layer
0
10.658
10.658
0
0.553
0
12
10.658
10.692
0.319009195
0.554
0.180831826
24
10.658
10.702
0.412835429
0.555
0.361663653
36
10.658
10.742
0.788140364
0.556
0.542495479
48
10.658
10.799
1.322949897
0.557
0.723327306
60
10.658
11.121
4.344154626
0.558
0.904159132
72
10.658
11.354
6.530305874
0.559
1.084990958
84
10.658
11.582
8.669544005
0.56
1.265822785
96
10.658
11.81
10.80878214
0.561
1.446654611
108
10.658
12.128
13.79245637
0.562
1.627486438
120
10.658
12.421
16.54156502
0.563
1.808318264
132
10.658
12.421
16.54156502
0.563
1.808318264
144
10.658
12.421
16.54156502
0.563
1.808318264
156
10.658
12.421
16.54156502
0.563
1.808318264
NIT ROURKELA
Wt. Change
Thickness
Thickness
Swelling
Page 51
Table–3.17 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at saline environment.
No. of
Time of
layers
immersion
Double
layer
0
14.752
0
0.736
0
12
14.854
0.69143167
0.738
0.27173913
24
14.986
1.586225597
0.74
0.543478261
36
15.285
3.613069414
0.742
0.815217391
48
15.587
5.660249458
0.744
1.086956522
60
15.921
7.924349241
0.746
1.358695652
72
16.231
10.02575922
0.748
1.630434783
84
16.752
13.55748373
0.75
1.902173913
96
17.254
16.96041215
0.752
2.173913043
108
17.753
20.34300434
0.754
2.445652174
120
18.285
23.94929501
0.756
2.717391304
132
18.285
23.94929501
0.756
2.717391304
144
18.285
23.94929501
0.756
2.717391304
156
18.285
23.94929501
0.756
2.717391304
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 52
Table–3.18 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at saline
environment.
No. of
Time of
layers
immersion
Triple
layer
0
15.513
0
1.095
0
12
15.999
3.132856314
1.099
0.365296804
24
16.487
6.278605041
1.102
0.639269406
36
16.956
9.301875846
1.106
1.00456621
48
17.541
13.07290659
1.11
1.369863014
60
17.982
15.91568362
1.114
1.735159817
72
18.421
18.74556823
1.118
2.100456621
84
18.924
21.98801006
1.122
2.465753425
96
19.421
25.19177464
1.126
2.831050228
108
19.862
28.03455167
1.13
3.196347032
120
20.102
29.5816412
1.134
3.561643836
132
20.102
29.5816412
1.134
3.561643836
144
20.102
29.5816412
1.134
3.561643836
156
20.102
29.5816412
1.134
3.561643836
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 53
Table–3.19 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (flexural) with immersion time expose at saline environment.
No. of
Time of
layers
immersion
Single
layer
0
14.044
0
0.582
0
12
14.103
0.420108231
0.583
0.171821306
24
14.204
1.139276559
0.584
0.343642612
36
14.312
1.908288237
0.585
0.515463918
48
14.432
2.762745657
0.586
0.687285223
60
14.514
3.346624893
0.587
0.859106529
72
14.617
4.080034178
0.588
1.030927835
84
14.734
4.913130162
0.589
1.202749141
96
14.854
5.767587582
0.59
1.374570447
108
14.921
6.244659641
0.591
1.546391753
120
14.921
6.244659641
0.591
1.546391753
132
14.921
6.244659641
0.591
1.546391753
144
14.921
6.244659641
0.591
1.546391753
156
14.921
6.244659641
0.591
1.546391753
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 54
Table–3.20 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (flexural) with immersion time expose at saline
environment.
No. of
Time of
layers
immersion
Double
layer
0
12.614
0
0.582
0
12
12.732
0.935468527
0.584
0.343642612
24
12.874
2.061201839
0.586
0.687285223
36
12.948
2.647851593
0.588
1.030927835
48
13.098
3.837006501
0.59
1.374570447
60
13.199
4.637704138
0.592
1.718213058
72
13.314
5.549389567
0.594
2.06185567
84
13.487
6.92088156
0.596
2.405498282
96
13.589
7.729506897
0.598
2.749140893
108
13.754
9.037577295
0.6
3.092783505
120
13.754
9.037577295
0.6
3.092783505
132
13.754
9.037577295
0.6
3.092783505
144
13.754
9.037577295
0.6
3.092783505
156
13.754
9.037577295
0.6
3.092783505
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 55
Table–3.21 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (flexural) with immersion time expose at saline
environment.
No. of
Time of
layers
immersion
Triple
layer
0
19.182
0
0.846
0
12
19.321
0.724637681
0.85
0.472813239
24
19.628
2.325096445
0.854
0.945626478
36
19.825
3.352100928
0.858
1.418439716
48
20.087
4.717964759
0.862
1.891252955
60
20.257
5.604212282
0.866
2.364066194
72
20.524
6.996142217
0.87
2.836879433
84
20.784
8.351579606
0.873
3.191489362
96
20.987
9.409863414
0.876
3.546099291
108
21.238
10.71838182
0.879
3.90070922
120
21.238
10.71838182
0.879
3.90070922
132
21.238
10.71838182
0.879
3.90070922
144
21.238
10.71838182
0.879
3.90070922
156
21.238
10.71838182
0.879
3.90070922
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 56
Table–3.22 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at saline environment.
No. of
Time of
layers
immersion
Single
layer
0
11.902
0
0.514
0
12
11.961
0.495715006
0.515
0.194552529
24
12.015
0.949420266
0.516
0.389105058
36
12.069
1.403125525
0.517
0.583657588
48
12.121
1.840026886
0.518
0.778210117
60
12.168
2.234918501
0.519
0.972762646
72
12.224
2.705427659
0.52
1.167315175
84
12.274
3.125525122
0.521
1.361867704
96
12.324
3.545622584
0.522
1.556420233
108
12.398
4.167366829
0.523
1.750972763
120
12.398
4.167366829
0.523
1.750972763
132
12.398
4.167366829
0.523
1.750972763
144
12.398
4.167366829
0.523
1.750972763
156
12.398
4.167366829
0.523
1.750972763
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 57
Table–3.23 Variation of weight gain and thickness swelling of untreated Luffa
Cylindrica fibre epoxy composite (tensile) with immersion time expose at saline
environment.
No. of
Time of
layers
immersion
Double
layer
0
11.599
0
0.601
0
12
11.717
1.01732908
0.603
0.332778702
24
11.835
2.03465816
0.605
0.665557404
36
11.953
3.05198724
0.607
0.998336106
48
12.071
4.06931632
0.609
1.331114809
60
12.189
5.0866454
0.611
1.663893511
72
12.307
6.103974481
0.613
1.996672213
84
12.425
7.121303561
0.615
2.329450915
96
12.543
8.138632641
0.617
2.662229617
108
12.661
9.155961721
0.619
2.995008319
120
12.661
9.155961721
0.619
2.995008319
132
12.661
9.155961721
0.619
2.995008319
144
12.661
9.155961721
0.619
2.995008319
156
12.661
9.155961721
0.619
2.995008319
NIT ROURKELA
Final Wt.
Wt. Change
Thickness
Thickness
Swelling
Page 58
Table–3.24 Variation of weight gain and thickness swelling of treated Luffa Cylindrica
fibre epoxy composite (tensile) with immersion time expose at saline environment.
No. of
Time of
Final Wt.
Wt. Change
Thickness
layers
immersion
Triple
layer
0
17.351
0
0.852
12
17.621
1.556106276
0.856
Thickness
Swelling
0
0.469483568
0.821596244
24
17.925
3.308166676
0.859
36
18.147
4.587631837
0.863
1.291079812
1.76056338
48
18.462
6.403089159
0.867
2.112676056
60
18.741
8.011065645
0.87
72
18.981
9.394271224
0.873
2.464788732
2.816901408
84
19.241
10.89274393
0.876
3.051643192
96
19.524
12.52377385
0.878
108
19.851
14.40839145
0.88
3.286384977
3.286384977
120
19.851
14.40839145
0.88
3.286384977
132
19.851
14.40839145
0.88
144
19.851
14.40839145
0.88
156
19.851
14.40839145
0.88
3.286384977
3.286384977
NIT ROURKELA
Page 59
Table-3.25
Environment
Distil Water
Saline Water
Table-3.26
Environment
Distil Water
Saline Water
NIT ROURKELA
Diffusion case selection parameters (Flexural Samples)
No. of
layers
Type of Fiber
n
k(h2)
SL
DL
TL
SL
Untreated
Untreated
Untreated
Alkali Treated
0.5523
1.0653
1.0855
1.0886
0.0682
0.0184
0.0501
0.0344
DL
TL
Alkali Treated
Alkali Treated
0.8983
0.6416
0.1175
0.4265
SL
DL
TL
SL
DL
TL
Untreated
Untreated
Untreated
Alkali Treated
Alkali Treated
Alkali Treated
1.0903
1.037
1.0497
1.0626
1.0687
1.0007
0.0293
0.022
0.0506
0.0164
0.035
0.1838
Diffusion case selection parameters (Tensile Samples)
No. of
layers
Type of Fiber
n
k(h2)
SL
Untreated
1.0975
0.0979
DL
Untreated
1.066
0.0179
TL
Untreated
0.9814
0.1338
SL
Alkali Treated
0.9126
0.0837
DL
Alkali Treated
1.0863
0.0549
TL
Alkali Treated
1.0832
0.0363
SL
Untreated
1.0626
0.0119
DL
Untreated
1.0315
0.0167
TL
Untreated
1.0311
0.0939
SL
Alkali Treated
1.0508
0.0227
DL
Alkali Treated
1.0052
0.0238
TL
Alkali Treated
1.0168
0.058
Page 60
Table-3.27
Diffusivity of untreated and treated fiber Luffa Cylindrica
fiber epoxy composites at different environments
Environment
Distil Water
Saline Water
Table-3.28
No. of
layers
Type of Fiber
Diffusivity
(Dx) x 10-4
SL
DL
TL
SL
DL
TL
Untreated
Untreated
Untreated
Alkali Treated
Alkali Treated
Alkali Treated
1.3235
4.7109
10.560
5.4702
3.0626
8.1415
SL
DL
TL
SL
DL
TL
Untreated
Untreated
Untreated
Alkali Treated
Alkali Treated
Alkali Treated
1.2311
3.3674
8.7999
4.4222
2.0858
4.0218
Diffusivity of untreated and treated fiber Luffa Cylindrica
fiber epoxy composites at different environments
Environment
Distil Water
Saline Water
NIT ROURKELA
No. of
layers
Type of Fiber
Diffusivity
(Dx) x 10-4
SL
DL
TL
SL
DL
TL
Untreated
Untreated
Untreated
Alkali Treated
Alkali Treated
Alkali Treated
2.2475
4.5690
8.6533
3.5448
3.7451
6.2147
SL
DL
TL
SL
DL
TL
Untreated
Untreated
Untreated
Alkali Treated
Alkali Treated
Alkali Treated
1.2457
3.8521
7.7462
3.5847
2.1458
6.0128
Page 61
Tensile strength (MPa)
60
50
40
30
Tensile strength
20
10
0
S0
S1
S2
S3
samples
Figure-3.6
Variation of tensile strength with different layers of
untreated Luffa Cylindrica fibre epoxy composites exposed
to saline water environment.
40
Flexural strength (MPa)
35
30
25
20
Flexural strength
15
10
5
0
S0
S1
S2
S3
Samples
Figure-3.7
Variation of flexural strength with different layers of
untreated Luffa Cylindrica fibre epoxy composites exposed
to saline water environment.
NIT ROURKELA
Page 62
80
Tensile strength (MPa)
70
60
50
40
30
Tensile strength
20
10
0
S0
S1
S2
S3
samples
Figure-3.8
Variation of tensile strength with different layers of
untreated Luffa Cylindrica fibre epoxy composites exposed
to distil water environment.
Flexural strength (MPa)
30
25
20
15
Flexural strength
10
5
0
S0
S1
S2
S3
Samples
Figure-3.9
Variation of flexural strength with different layers of
untreated Luffa Cylindrica fibre epoxy composites exposed
to distil water environment.
NIT ROURKELA
Page 63
90
80
Tensile Strength
70
60
50
40
Tensile Strength
30
20
10
0
S0
S1
S2
S3
Sample
Figure-3.10
Variation of tensile strength with different layers of treated
Luffa Cylindrica fibre epoxy composites exposed to saline
water environment.
Flexural strength (MPa)
70
60
50
40
30
Flexural strength
20
10
0
S0
S1
S2
S3
Samples
Figure-3.11
Variation of flexural strength with different layers of
treated Luffa Cylindrica fibre epoxy composites exposed to
saline water environment.
NIT ROURKELA
Page 64
120
100
Flexural Strength
80
60
Tensile Strength
40
20
0
S0
S1
S2
S3
Sample
Figure-3.12
Variation of tensile strength with different layers of treated
Luffa Cylindrica fibre epoxy composites exposed to distil
water environment.
70
60
Flexural Strength
50
40
30
Flexural Strength
20
10
0
S0
S1
S2
S3
Sample
Figure-3.13
Variation of flexural strength with different layers of
treated Luffa Cylindrica fibre epoxy composites exposed to
distil water environment.
NIT ROURKELA
Page 65
Thickness Swelling
Moisture Absorption
4
3.5
3
2.5
2
SL
1.5
DL
1
TL
0.5
0
0
50
100
150
200
Time of Immersion
Figure-3.14
Variation of thickness swelling of untreated Luffa
Cylindrica fibre epoxy composites (tensile) with immersion
time at saline water environment.
Thickness Swelling
3.5
3
Axis Title
2.5
2
SL
1.5
DL
1
TL
0.5
0
0
50
100
150
200
Axis Title
Figure-3.15
Variation of thickness swelling of treated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
saline water environment.
NIT ROURKELA
Page 66
Moisture Absorption
Thickness Swelling
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.16
Variation of thickness swelling of untreated Luffa
Cylindrica
fibre
epoxy
composites
(flexural)
with
immersion time at saline water environment.
Thickness Swelling
Moisture Absorption
3.5
3
2.5
2
SL
1.5
DL
1
TL
0.5
0
0
50
100
150
200
Time of Immersion
Figure-3.17
Variation of thickness swelling of treated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
saline water environment.
NIT ROURKELA
Page 67
Moisture Absorption
Thickness Swelling
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.18
Variation of thickness swelling of untreated Luffa
Cylindrica fibre epoxy composites (tensile) with immersion
time at distil water environment.
Thickness Swelling
Moisture Absorption
3.5
3
2.5
2
SL
1.5
DL
1
TL
0.5
0
0
50
100
150
200
Time of Immersion
Figure-3.19
Variation of thickness swelling of treated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
distil water environment.
NIT ROURKELA
Page 68
Moisture Absorption
Thickness Swelling
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.20
Variation of thickness swelling of untreated Luffa
Cylindrica
fibre
epoxy
composites
(flexural)
with
immersion time at distil water environment.
Thickness Swelling
3.5
3
Thickness Swelling
2.5
2
SL
1.5
DL
1
TL
0.5
0
0
50
100
150
200
Time of Immersion
Figure-3.21
Variation of thickness swelling of treated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
distil water environment.
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Weight Change
Moisture Absorption
35
30
25
20
SL
15
DL
10
TL
5
0
0
50
100
150
200
Time of Immersion
Figure-3.22
Variation of weight gain of the untreated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
saline water environment.
Moisture Absorption
Weight Change
18
16
14
12
10
8
6
4
2
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.23
Variation of weight gain of the treated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
saline water environment.
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Moisture Absorption
Weight Change
20
18
16
14
12
10
8
6
4
2
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.24
Variation of weight gain of the untreated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
saline water environment.
Moisture Absorption
Weight Change
20
18
16
14
12
10
8
6
4
2
0
Sl 3
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.25
Variation of weight gain of the treated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
saline water environment.
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Weight Change
Moisture Absorption
25
20
15
SL 2
10
DL 2
5
TL 1
0
0
50
100
150
200
Time of Immersion
Figure-3.26
Variation of weight gain of the untreated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
distil water environment.
Weight Change
Moisture Absorption
24
20
16
'UT' SL
12
'UT' DL
8
'UT' TL
4
0
0
50
100
150
Time of Immersion
Figure-3.27
Variation of weight gain of the treated Luffa Cylindrica
fibre epoxy composites (tensile) with immersion time at
distil water environment.
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Moisture Absorption
Weight Change
20
18
16
14
12
10
8
6
4
2
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.28
Variation of weight gain of the untreated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
distil water environment.
Wt. after successive immersion
Weight Change
20
18
16
14
12
10
8
6
4
2
0
SL
DL
TL
0
50
100
150
200
Time of Immersion
Figure-3.29
Variation of weight gain of the treated Luffa Cylindrica
fibre epoxy composites (flexural) with immersion time at
distil water environment.
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Page 73
35
Moisture Absorption (%)
30
25
20
Distil
15
Saline
10
5
0
SL
DL
TL
No. of Layers
Figure-3.30
Maximum
moisture
absorption
of
untreated
Luffa
Cylindrica fiber epoxy composite (tensile samples) versus
fiber loading in both the environments
20
Moisture Absorption (%)
18
16
14
12
10
Distil
8
Saline
6
4
2
0
SL
DL
TL
No. of Layers
Figure-3.31
Maximum
moisture
absorption
of
untreated
Luffa
Cylindrica fiber epoxy composite (flexural samples) versus
fiber loading in both the environments
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Moisture Absorption (%)
25
20
15
Distil
Saline
10
5
0
SL
DL
TL
No. of Layers
Figure-3.32
Maximum moisture absorption of treated Luffa Cylindrica
fiber epoxy composite (tensile samples) versus fiber loading
in both the environments
20
Moisture Absorption (%)
18
16
14
12
10
Distil
8
Saline
6
4
2
0
SL
DL
TL
No. of Layers
Figure-3.33
Maximum moisture absorption of treated Luffa Cylindrica
fiber epoxy composite (flexural samples) versus fiber
loading in both the environments
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y = 1.0975x - 2.6537
y = 1.066x - 2.3653
y = 0.9814x - 2.0219
0
SL
-0.4
DL
log (Mt/Mm)
-0.2
-0.6
TL
-0.8
Linear (SL)
-1
Linear (DL)
-1.2
Linear (TL)
-1.4
-1.6
1
1.2
1.4
1.6
1.8
2
2.2
log (t)
Figure-3.34
Example Diffusion curve fitting for Luffa Cylindrica fiber
epoxy composites under Different environments
Figure-3.35
Example Plot of percentage of moisture absorption versus
square root of time for calculation of Difusivity
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Page 76
0.1
log(Mm/Mt)
-0.1
-0.3
SL
DL
-0.5
TL
-0.7
-0.9
1
1.4
Figure-3.36
1.8
log(t)
2.2
Variation of log (Mt/Mm) with log (t) for untreated Luffa
Cylindrica fiber epoxy composites (flexural) at distil water
environment
0
-0.2
log (Mt/Mm)
-0.4
SL
-0.6
DL
-0.8
TL
-1
-1.2
-1.4
-1.6
1
1.2
1.4
1.6
1.8
2
2.2
log (t)
Figure-3.37
Variation of log (Mt/Mm) with log (t) for untreated Luffa
Cylindrica fiber epoxy composites (tensile) at distil water
environment
NIT ROURKELA
Page 77
log (Mt/Mm)
0
-0.2
SL
-0.4
DL
TL
-0.6
-0.8
-1
1
1.4
1.8
2.2
log (t)
Figure-3.38
Variation of log (Mt/Mm) with log (t) for treated Luffa
Cylindrica fiber epoxy composites (flexural) at distil water
environment
0
log (Mt/Mm)
-0.2
-0.4
SL
DL
-0.6
TL
-0.8
-1
1
1.4
1.8
2.2
log (t)
Figure-3.39
Variation of log (Mt/Mm) with log (t) for treated Luffa
Cylindrica fiber epoxy composites (tensile) at distil water
environment
NIT ROURKELA
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0
log (Mt/Mm)
-0.2
-0.4
SL
-0.6
DL
-0.8
TL
-1
-1.2
1
1.4
1.8
2.2
log (t)
Figure-3.40
Variation of log (Mt/Mm) with log (t) for untreated Luffa
Cylindrica fiber epoxy composites (flexural) at saline water
environment
0
log (Mt/Mm)
-0.2
-0.4
SL
-0.6
DL
-0.8
TL
-1
-1.2
-1.4
1
1.4
1.8
2.2
log (t)
Figure-3.41
Variation of log (Mt/Mm) with log (t) for untreated Luffa
Cylindrica fiber epoxy composites (tensile) at saline water
environment
NIT ROURKELA
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0
log (Mt/Mm)
-0.2
-0.4
-0.6
SL
-0.8
DL
-1
TL
-1.2
-1.4
1
1.4
1.8
2.2
log (t)
Figure-3.42
Variation of log (Mt/Mm) with log (t) for treated Luffa
Cylindrica fiber epoxy composites (tensile) at saline water
environment
0
log (Mt/Mm)
-0.2
-0.4
SL
-0.6
DL
-0.8
TL
-1
-1.2
-1.4
1
1.4
1.8
2.2
log (t)
Figure-3.43
Variation of log (Mt/Mm) with log (t) for treated Luffa
Cylindrica fiber epoxy composites (flexural) at saline water
environment
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Chapter 4
REFERENCES
Chapter-4
4.
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