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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.