chapter 3 materials and methods 3.1...
TRANSCRIPT
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CHAPTER 3
MATERIALS AND METHODS
3.1 Introduction This chapter presents the details of various fibers used, comparison of mechanical
properties of fibers used with standard fibers, chemical pre-treatment given to the natural
fibers, method of preparation of composite samples and mechanical testing procedures. Two
types of natural fibers namely vetiver and jute and one synthetic fiber namely E-glass were
used as reinforcements in vinyl ester matrix resin. Vetiver fibers were given alkali treatment
and heat treatment to improve its surface properties. Hand layup method is used to prepare
ten composite samples with varying proportions of fibers. This chapter also discuss the
ASTM standards for mechanical testing.
3.2 Constituents of Composites
3.2.1 Reinforcements
The present research uses three types of reinforcements for preparation of hybrid
composites. Out of the three reinforcements, two are natural fibers namely vetiveria
zizanioides and jute and one is synthetic namely E-glass. Vetiveria zizanioides is a perennial
grass and it is commonly called as vetiver. It has wide applications in medicine, perfumery
frozen food refrigeration and in preparation of drinks. In agriculture, it is used as mulch,
compost, nursery block, animal feed stuff, mushroom cultivation and botanical pesticides.
In construction field it is used as roof thatch, hut, mud brick, vetiver - clay storage bin, ash
for concrete and straw bale. It also finds applications in pottery, melamine utensils and water
containers, bouquet and handicraft works. The aromatic fragrance of vetiver root oil are used
in blending of cosmetics, perfumes scenting of soaps (Balasankar et al. 2013).
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Figure 3.1 Schematic of raw vetiver fibers
Vetiver has a density of 1.5 g/cm3 which is less than the density of cotton and
equivalent to the density of other fibers like abaca, flax, ramie and sisal. It has a diameter in
the range between 100 µm to 220 µm. The maximum tensile strength of vetiver fiber is 723
MPa, which is higher than abaca, alfa, bagasse, bamboo, banana, coconut, coir, cotton, kenaf
and nettle. Its maximum Young’s modulus is about 49.8 GPa which is higher than abaca,
alfa, bagasse, banana, coconut, coir, hemp, jute, kenaf, licuri and ramie fibers. The failure
strain of vetiver is about 2.4 % which is higher than bamboo, curaua, hemp, jute, kenaf,
nettle and pine apple. Hence the overall properties of vetiver fiber are comparable with some
standard natural fibers. The vetiver fibers used for the present research is in the form of
random form as presented in Figure 3.1.
Figure 3.2 Schematic of woven jute fiber mat
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Jute (Corchorus Oliotorus) is a commercially available fiber and cultivated mostly in
Asian countries. Jute is available in the form of random fibers, twisted yarns, ropes and mats.
It finds wide applications as sacks, bags, bedding foundations, packaging textiles and now a
day’s jute is also replacing the wood for pulp in paper industry. Jute is subjected to several
treatments before it reaches the market and hence it is readily usable. Jute has a density of
1.3 g/cm3 which is less than the density of abaca, cotton, curaua, flax, ramie, sisal and
vetiver.
Jute has a diameter of 260 µm. It has a maximum tensile strength of 773 MPa and
Young’s modulus of 27 GPa which are more than some common fibers like abaca, alfa,
bagasse, banana, coconut, coir, cotton, date palm, henequen, pineapple, ramie and sisal.
Failure strain of jute is 1.4 % which is somewhat lesser but equivalent to bamboo and
pineapple fibers. Jute is also having comparable mechanical properties with some common
natural fibers. The jute fibers used for the present research is in the form of woven mat as
presented in Figure 3.2.
Glass is one among the several synthetic fibers which is man-made and widely used
as reinforcements in composites over the few decades. It has several good properties than
other synthetic fibers like carbon and aramids. Glass fibers are classified as low cost general
purpose fibers and special purpose fibers. These fibers are known by their initials each
specifying a property. Some glass fibers are E-glass having low electrical conductivity, S-
glass having high strength, C-glass having high chemical durability, M-glass having high
modulus, A-glass is having high alkali content, D-glass having low dielectric constant and
R-glass is used where the applications needs more strength and corrosion resistance.
E-glass fibers have a comparable properties with other synthetic fibers. It is available
with a diameter ranging from 9 µm to 15 µm and has a density of 2.5 g/cm3. It has a
maximum tensile strength of 3500 MPa, Young’s modulus of 70 GPa and a failure strain of
2.5 %. The glass fibers used for the present research is E-glass mat as presented in Figure
3.3.
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Figure 3.3 Schematic of E-glass fiber mat
3.2.2 Matrix resin
The matrix resin used in the present research is vinyl ester. Vinyl ester is a thermoset
resin and a product of addition polymerization of different epoxide resins and unsaturated
monocarboxylic acids like methacrylic acid. The molecular structure of vinyl ester is similar
to polyester but in location of their reactive sites, that is they are positioned at the ends of
molecular chains. Figure 3.4 presents the preparation of bisphenol-A based vinyl ester resin
by the reaction between bisphenol-A glycidylether and methacrylic acid. The reactive groups
forms a cross-linked network with or without a co-monomer. In general, vinyl ester resins
are diluted with a monomer of low molecular weight such as, styrene, vinyl toluene and
methyl methacrylate in order to reduce its viscosity.
Vinyl ester has high shock absorbing capacity and it is more resilient and tougher than
polyester. Vinyl ester has fewer ester groups which enhances the ability to resist water and
chemicals absorption and find applications in pipe lines and chemical storage tanks. As vinyl
ester is less prone to hydrolysis, they are used as a barrier or skin coat for polyester
components which are immersed in water such as boat hulls. Vinyl ester resin has a tensile
strength of 80 MPa and tensile modulus of 3.6 MPa. The failure strain of vinyl ester is 4 %
and a heat deflection temperature of 1000C. It has a flexural strength of 140 MPa and flexural
modulus of 0.372 MPa (Watt & Perov 1985). Many properties of vinyl ester rein are in
between epoxy and polyester resins. Vinyl ester has a viscosity of 200 cp and its increased
bond strength helps proper bonding with core materials.
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Figure 3.4 Preparation of Vinyl ester resin
3.3 Pre-treatment to fibers The raw vetiver fiber has been purchased from a local supplier in bulk and thoroughly
washed in distilled water to remove the impurities present in it. Then the fiber was soaked
in 5% of sodium hydroxide solution for about 2 hours. The alkali treatment helps for removal
of unwanted soluble celluloses, pectin, lignin, etc. During this treatment, a fiber to solution
ratio of 1: 25 was maintained. After 2 hours the fiber was again washed in distilled water to
remove excess sodium hydroxide. Then the fiber is dried in sunlight for about 5 hours and
then heated in furnace at 60°C for about 4 hours (Li Ma et al. 2012).
Figure 3.5 Alkali treatment to vetiver fibers
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The alkali treatment and furnace heating of fibers are presented in Figure 3.5 and
Figure 3.6. Aspect ratio is an important parameter to be considered while manufacturing of
composites. It is defined as the ratio of length to the diameter of fiber (l/d). A proper selection
of aspect ratio controls the fiber dispersion and resin – fiber bonding and hence improves
the mechanical properties of composites. The average diameter of vetiver root is found to be
1.5 mm and the roots are cut to a length of 35 mm.
Figure 3.6 Furnace heating of vetiver fibers
3.4 Hand Layup Processing
Hand lay up or wet layup method is one of the oldest and easiest methods for
production of FRP. This method could be used for preparing composites up to a maximum
of a swimming pool area of about 1600 square feet. But this method is limited to production
of simple shapes and for limited volume operation. This method uses a mould surface over
which a layer of release agent and gel coat is applied before introducing the resin. Then the
resin layer was placed over the mould followed by the fiber in the form of particles or mats
distributed evenly over the resin layer. Next was again the resin layer spread over the fiber
layer and a roller helps to distribute the resin all around the fiber. This process was repeated
until the maximum thickness intended is obtained. Finally a dead weight is placed over the
mould for about 8 hours for proper settling and bonding. In the present study, composites
samples are prepared with a dimension 600 mm x 600 mm x 12 mm keeping in mind that
the samples are intended for mechanical testing as well as machining.
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Figure 3.7 Sample preparation by hand layup method
Ten composite samples were prepared by varying the proportions of fibers. The
selection of fiber and resin proportions is based on the survey of previous literatures (Gilles
Sebe et al. 2000; Dwivedi & Navin Chand 2009; Ruhul Khan et al. 2010). The proportions
of fibers are varied in each sample but maintained at 34 wt% in total and the resin proportion
was maintained as 66 wt% in all samples. During this preparation methyl ethyl ketone
peroxide was used as a catalyst and cobalt octoate was used as an accelerator. The fiber
proportions in each sample are presented in Table 3.1.
In order to study the impact of fiber pre-treatment on the mechanical properties, two
composite samples are prepared with untreated vetiver fibers and hence are named as UV
representing untreated vetiver. All remaining samples are named as TV representing treated
vetiver. In order to study the influence of vetiver, jute and glass fibers the ten samples are
classified in to three groups namely vetiver/glass composites containing only vetiver and
glass fibers, vetiver/jute composites containing only vetiver and jute fibers and
vetiver/jute/glass composites containing all the three fibers.
Sample 1 was prepared with a combination of 17 wt% of untreated vetiver and 17 wt%
of glass and named as UV17G17. Sample 2 was prepared with a combination of 10 wt% of
treated vetiver and 24 wt% of glass and named as TV10G24. Sample 3 was prepared with
17 wt% of vetiver and 17 wt% of glass and named as TV17G17. Sample 4 eas prepared in
the combination of 24 wt% of vetiver and 10 wt% of glass and named as TV24G10. Sample
5 was prepared with a combination of 17 wt% of untreated vetiver and 17 wt% of jute and
named as UV17J17. Sample 6 was prepared with a combination of 10 wt% of treated
vetiver and 24 wt% of jute and named as TV10J24. Sample 7 was prepared with 17 wt% of
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vetiver and 17 wt% of jute and named as TV17J17. Sample 8 was prepared in the
combination of 24 wt% of vetiver and 10 wt% of jute and named as TV24J10. Sample 9 was
prepared in the combination of 13 wt% of vetiver and 13 wt% of jute and 8 wt% of glass and
named as TV13J13G8. Sample 10 was prepared in the combination of 10 wt% of vetiver
and 10 wt% of jute and 14 wt% of glass and named as TV13J13G14.
Table 3.1 Composition of samples
S. No. Sample Vetiver (wt %) Jute (wt %) Glass (wt %) Resin (wt %)
1. UV17G17 17 (untreated) - 17 66 2. TV10G24 10 (treated) - 24 66 3. TV17G17 17 (treated) - 17 66 4. TV24G10 24 (treated) - 10 66 5. UV17J17 17 (untreated) 17 - 66 6. TV10J24 10 (treated) 24 - 66 7. TV17J17 17 (treated) 17 - 66 8. TV24J10 24 (treated) 10 - 66 9. TV13J13G8 13 (treated) 13 8 66 10. TV10J10G14 10 (treated) 10 14 66
3.5 Mechanical testing
A structural component is mostly subjected to four types of stresses namely, tensile
stress, bending stress, compressive stress and impact stress. As the composite developed in
the present study is aimed to use in structural components, the work only deals with the
tensile, flexural, compressive and impact testing. Tensile and compressive tests were done
in universal testing machine according to ASTM D638 and ASTM D695 standards
respectively. During tensile testing, the samples were cut in the shape of dog bone with a
gauge length of 50 mm. Flexural tests were conducted as per ASTM D790 and impact tests
were conducted as per ASTM D256 standards. During three point flexural testing, the
samples were cut in to rectangular bar with a span length of 192 mm and a depth of 12 mm
(span to depth ratio 16:1). The loading and supporting nose radii are maintained at 4 and 1.6
times the specimen thickness respectively. Charpy impact test was done using a pendulum
type impact testing center during which, the notch angle of the sample is maintained as 450.
The schematic of mechanical tests carried out are presented from Figure 3.8 to Figure 3.11.
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Figure 3.8 Tension testing
Figure 3.9 Compression testing
Figure 3.10 Flexural testing
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Figure 3.11 Impact testing
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Summary
This chapter addressed the properties and preparatory methods of different natural and
synthetic fibers used in the present work. The chapter also gave a clear picture of
comparative analysis of all natural and synthetic fibers.
The chemical pre-treatment to natural fibers and followed by heat treatment in sunlight
and heating furnace were done to improve the bonding ability of fibers with the matrix
resin.
Hand layup method is one of the easiest and simplest method for preparation of FRP
starting from small plates to large sized bath tubs. The steps involved in hand layup
method was clearly addressed.
Ten samples were prepared by changing the compositions of natural and synthetic
fibers and keeping the resin composition as a constant.
The size and shape of samples for tensile, compression, flexural and impact testing
were discussed.