EXPERIMENTAL TESTING ON MECHANICAL PROPERTIES OF ...ural bers on mechanical properties of epoxy...

EXPERIMENTAL TESTING ONMECHANICAL PROPERTIES OFVARIOUS NATURAL FIBERS

REINFORCED EPOXY HYBRIDCOMPOSITES

S.Sathisha1, K.Kumaresanb2, L.Prabhuc3,S.Gokulkumard4 and S.Dineshe5

Department of Mechanical Engineering1 3 4 5Assistant Professor,

KPR Institute of Engineering and Technology, Coimbatore2Professor,

Park College of Engineering and Technology, [email protected]

December 28, 2017

Abstract

The role of natural fibers in polymer matrix compos-ites have widely increased due to their mechanical proper-ties like high specific strength, good corrosion resistance,high stiffness and high fatigue strength etc. Various natu-ral fibers such as banana, bamboo, ramie, coir, sisal, jute,flax, pineapple and kenaf fibers are used as reinforcementsin polymer composites and appear more attractive due totheir low density, recyclability, easily availability and lessCO2 emission. In this work sisal, kenaf, flax and pineapplefibers are used as a reinforcements and epoxy resin is usedas a matrix to produce various hybrid composites by com-pression molding techniques. Tensile, impact and flexural

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International Journal of Pure and Applied MathematicsVolume 118 No. 16 2018, 873-888ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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tests were carried out for pineapple / sisal / epoxy, kenaf /sisal / epoxy, pineapple / kenaf / epoxy, flax / pineapple /epoxy and flax / kenaf / epoxy composites and their resultsare compared. A flax / kenaf / epoxy composite shows bet-ter tensile, impact and flexural strength compared to otherhybrid composites.

Keywords : Sisal; kenaf; flax; pineapple; epoxy.

1 Introduction

In recent years, natural fiber composites are used in many engi-neering applications due to various desirable properties that theyoffer such as light weight, renewability, low cost and environmen-tally friendly. Natural fiber composites are used in many industriessuch as automotive, sporting goods, marine, electrical, construc-tion, and household appliances. Kenaf, sisal, coir, banana, juteflax, pulp, wood flour, oil palm, pineapple leaf and coir are themain natural fibers used as reinforcements. Kenaf fibers providehigh stiffness and strength values. They also have higher aspect ra-tios making them suitable to be used as reinforcement in polymercomposites. Pineapple Leaf Fiber (PALF) serving as reinforcementfiber in most of the plastic matrix has shown its significant role asit is cheap, exhibiting superior properties when compared to othernatural fiber. PALF is a multi-cellular and lignocelluloses materialextracted from the leaves of plant Ananas cosomus belonging to theBromeliaceae family by retting (separation of fabric bundles fromthe cortex). PALF has a ribbon-like structure and is cemented to-gether by lignin material, which contributes to the Strength of thefiber. In recent years, there is a growing interest in the use of biofibers as reinforcing components for thermoplastics and thermosets.Sisal fiber, a member of the Agavaceae family is a biodegradableand environmental friendly crop. Moreover, sisal is a strong, stableand versatile material and it has been recognized as an importantsource of fiber for composites. One of the best-known natural fibersis kenaf fiber, which is used for a variety of applications. Kenaf (Hi-biscus cannabinus L.) is a high-yielding cordage crop traditionallygrown for the production of twine, rope and sackcloth. Newer ap-plications for kenaf include paper products, building materials andabsorbents. The main drawbacks of natural fiber reinforced com-

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International Journal of Pure and Applied Mathematics Special Issue

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posites are their water sensitivity, poor dimensional stability, pooradhesion to basically all matrix polymers, and poor processabilityat high fiber contents. Chemical treatment of the natural fiber canhelp to overcome such drawbacks to enhance the bonding betweenfiber and the matrices, resulting in improved properties of fiber re-inforced composites. Different chemical treatment methods suchas alkali treatment, silane treatment, benzoylation treatment, per-manganate treatment and peroxide treatment have been applied onthe various natural fibers to improve their strength and the fibermatrix interface by converting them into hydrophobic nature. Al-kaline treatment is used to improve bonding strength between fiberand matrix and dynamic flexural modulus of the composites. Theaim of this research work is to investigate the effect of various nat-ural fibers on mechanical properties of epoxy hybrid composites.

2 Materials and methods

2.1 Sisal fiber

Sisal fibers are stiff fibers extracted from an agave plant. Thesefibers are straight, smooth and yellow in colour. Strength, dura-bility and ability to stretch are some important properties of sisalfibers. It was collected from M/s Tokyo Engineering Corporation,Coimbatore.

2.2 Pineapple fiber

PALF is one such fiber source known from a long time obtained fromthe leaves of pineapple plant (Ananas comosus) from the family ofBromeliaceae. It was obtained from local dealers.

2.3 Flax fiber

Flax fibers come from the flax plant; one species of Linum usitatis-simumis bred, and is widely cultivated in West Europe where thedaily temperature is generally below 30 C. The flax plant has a lifecycle of 90125 days including vegetative, flowering and maturationperiods. The diameter of the flax stem is in the range of 12 mm,

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with a height of about 80 cm. It was obtained from TMG textilesand garments, Coimbatore.

2.4 Kenaf fiber

Kenaf (Hibiscus cannabinus L.) is a traditional, third world cropafter wood and bamboo that is poised to be introduced as a newannually renewable source of industrial purpose in the so calleddeveloped economies. Kenaf is a warm-season annual fiber cropgrowing in temperate and tropical areas. It is related to cotton,okra, and hibiscus due to systematic. It is a fibrous plant, consistingof an inner core fiber (7560%), which produces low quality pulp, andan outer bast fiber (2540%), which produces high quality pulp, inthe stem. It was obtained from local dealers.

2.5 Matrix and Hardener

Epoxy resin (LY556) is used as a matrix which was purchased fromM/s covai seenu & company, Coimbatore. Hardener HY 951 is ayellowish-green liquid. Hardener HY 951 obtained from M/s covaiseenu & company, Coimbatore, India has been used as a curingagent. In the present investigation, 10% by weight has been usedin all material developed.

2.6 Chemical treatment

Interfacial bonding between fiber and matrix plays a vital role infinding the mechanical properties of the composites. Since appliedstress is transferred between matrix and fibers across the inter-face, good interfacial bonding is required to achieve optimum rein-forcement although, it is possible to have an interface that is toostrong, enabling crack propagation which can reduce toughness andstrength. However, for plant based fiber reinforced composites thereis usually limited interaction between the hydrophilic fibres and ma-trices which are commonly hydrophobic leading to poor interfacialbonding limiting mechanical performance as well as low moisture re-sistance affecting long term properties. For bonding to occur, fiberand matrix must be brought into intimate contact; wettability canbe regarded as an essential precursor to bonding. Insufficient fiber

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wetting results in interfacial defects which can act as stress concen-trators. Fiber wettability has been shown to affect the toughness,tensile and flexural strength of composites. Chemical treatment canimprove the wettability of the fiber and thus improve the interfacialstrength. Interfacial bonding can occur by means of mechanismsof mechanical interlocking, electrostatic bonding, chemical bond-ing and inter-diffusion bonding. Mechanical interlocking occurs toa greater extent when the fiber surface is rough and increases theinterfacial shear strength.

Figure 1: Chemical prepara-tion

Figure 2: Fibers immersed insolution

For that, alkali treatment or mercerization using sodium hydrox-ide (NAOH) is the most commonly used treatment for bleachingand cleaning the surface of natural fibers to produce high-qualityfibers. 5% NaOH solution was prepared using sodium hydroxidepellets and distilled water. Pineapple, sisal, flax and kenaf fiberswere then dipped in the solution for 2hours separately. Chemicalpreparation and fibers immersed in solution are shown in Fig. 1and Fig. 2 respectively. Then it was washed in running water. Itwas then kept in hot air oven for 3hours at 80C. Fibers placed inhot air oven is shown in Fig. 3.

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Figure 3: Fibers placed in Hot airoven Figure 4: Fibers stacking

2.7 Preparation of composites

Fiber configuration and volume fraction are the two important fac-tors that influence the properties of the composite. In this research,the long fibers are used as a reinforcement and epoxy resin used asa matrix to the weight fraction of 40% and 60% respectively toprepare the composites. First, the mould was polished and then amould releasing agent was applied on the surface used to facilitateeasy removal of the composite from the mold after curing. Thelow temperature curing epoxy resin LY556 and the correspondinghardener (HY951) were mixed in a ratio of 10:1 by weight as recom-mended. The mixing was done thoroughly before the mixture filledinto the mould and pressed in a hydraulic press at the temperatureof 130C for 30 minutes and a pressure of 35 kg/cm for 30 minutesis applied before it is removed from the mould. Then, this sam-ple is post cured at standard atmosphere for some period of timeto study the effect of post curing time on mechanical properties.Fibers stacking arrangement shown in Fig. 4.

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3 Mechanical Tests

3.1 Tensile test

The tensile test specimen was prepared according to the ASTMD3039 standard. The dimensions, gauge length and cross-headspeeds were chosen according to the ASTM D3039 standard. Atensile test involves mounting the specimen in a machine and sub-jecting it to the tension. The testing process involves placing thetest specimen in the testing machine and applying tension to ituntil it fractures.

3.2 Impact test

Impact property of a composite is the measure of the total energydissipated in the material before its final failure occurs under shockloading. The impact test samples are cut from respective compos-ites as per the ASTM A370 standard and tested in the izod impacttesting machine.

3.3 Flexural test

The flexural specimens were prepared as per the ASTM D790 stan-dard. The 3-point flexure test is the most common flexural testfor composite materials. Specimen deflection is measured by thecrosshead position. Test results include flexural strength and dis-placement. The testing process involves placing the test specimenin the universal testing machine and applying force to it until itfractures and breaks.

4 Results and Discussion

The hybrid composite samples are tested in their correspondingdigitalized machines and the tensile, flexural and impact propertiesare determined. The strength of composite samples generated withrespect to various natural fibers to be reinforced in present below.The results indicated that Flax/Kenaf/Epoxy hybrid composite ex-hibited better mechanical properties and maximum values observedare 28.36 MPa as tensile strength, 94.42 MPa as flexural strength

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and 3.15 joules as impact strength. It was clear that tensile strengthof the hybrid composite increased with 20% volume fraction of flaxcombined with 20% volume fraction of kenaf fiber. Tensile modulusalso improved with increasing flax fiber in the composites. This isbecause the tensile strength and youngs modulus of flax and kenafare much higher than the other fibers.

Table 1: Tensile Test Values

S.NoTypes ofHybrid Composite

UltimateTensileLoad(N)

TensileStrength(MPa)

Elongationat Break(%)

1 Pineapple/Sisal/Epoxy 2356.42 18.84 2.542 Kenaf/Sisal/Epoxy 3104.75 20.64 1.443 Pineapple/kenaf/Epoxy 2444.65 19.53 1.204 Flax/Pineapple/Epoxy 3188.25 24.82 2.575 Flax/Kenaf/Epoxy 3547.45 28.36 1.42

Table 1 shows the value of tensile strength of pineapple / sisal/ epoxy, kenaf / sisal / epoxy, pineapple / kenaf / epoxy, flax /pineapple / epoxy and flax / kenaf / epoxy hybrid composites. Ac-cording to the results, the flax / kenaf / epoxy composite exhibitsmaximum tensile strength compared to other hybrid compositesdue to presence of other natural fibers which having poor adhesivestrength and high formation of void content during compression.However, to obtain the polymer composites with better mechanicalproperties, the interaction between fiber and matrix need to be im-proved. The flax/kenaf/epoxy composite showed an increase in thetensile modulus and strength with addition of 20% volume fractionof kenaf fiber with flax fibers and there was a decrease in the tensileproperties with addition of other fibers like sisal and pineapple toflax fibers.

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Table 2: Impact Test Values


ImpactStrength(J)

1 Pineapple/Sisal/Epoxy 1.852 Kenaf/Sisal/Epoxy 1.903 Pineapple/kenaf/Epoxy 2.154 Flax/Pineapple/Epoxy 2.755 Flax/Kenaf/Epoxy 3.15

Table 2 shows the comparison of impact strength of pineapple/ sisal / epoxy, kenaf / sisal / epoxy, pineapple / kenaf / epoxy,flax / pineapple / epoxy and flax / kenaf / epoxy hybrid compos-ites. From the result, it can be observed that flax / kenaf / epoxycomposite exhibits maximum impact strength compared to otherhybrid composite which can hold impact load of 3.15 joules. It isclearly observed that when the kenaf fiber was added to the flaxfiber, impact strength significantly increased comparing to othercombinations.

Table 3: Flexural Test Values


FlexuralLoad(N)

FlexuralStrength(MPa)

1 Pineapple/Sisal/Epoxy 184.57 59.602 Kenaf/Sisal/Epoxy 249.83 90.093 Pineapple/kenaf/Epoxy 238.38 88.054 Flax/Pineapple/Epoxy 140.13 36.775 Flax/Kenaf/Epoxy 272.62 94.42

Table 3 shows the value of flexural strength of various hybridcomposites. From that result flax/kenaf/epoxy hybrid compositegives maximum flexural strength (94.42 MPa) compared to othertwo hybrid composites. It has been noted that, the flexural strengthincreases with the increase of flexural load then it tends to break.With the high flexural strength and flexural modulus for the flaxcomposite with 20% volume fraction of kenaf fiber and the reductionin the flexural properties with the pineapple and sisal fibers. Fromthe experimentation, it could be concluded that combinations of20% volume fraction of flax and 20% volume fraction of kenaf is the

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higher limit for fiber load for the flax composites when consideringthe flexural properties.

Figure 5: Tested Specimens

The five different hybrid composites of specimens are testedtheir tensile, impact and flexural strength from respective machines.Impact test carried out in izod impact testing machine and bothtensile and flexural testing were carried out in universal testingmachine. Fig. 5 shows tested specimens of five different hybridcomposites.

4.1 SEM Analysis

For morphological study, the scanning electron microscope was usedto reveal fractured surface of composites which together bonded be-tween the fiber and matrix. In this work, scanning electron micro-scope was used to study the measure of adhesiveness and interactionbetween natural fibers and epoxy resin. For pineapple/sisal com-posites, there was hindrance of fibers which tried to hold up uniformresin by applied load and which were shows less surface roughnessof fiber tends to weaken the bonding strength and fiber pull out.This was identified by air bubbles formation over the sample sur-face. For kenaf/sisal, the reinforcement was not distributed evenlyover the matrix due to bunch of sisal fiber can be observed. Thismicrograph has highest percentage of void content by fiber pull out.As for flax/kenaf, both alkali treated fibers were aligned perfectlywith epoxy resin. Due to poor surface roughness of fibers, aspectratio were increased which causes better adhesion between fiber and

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resin. Fig. 6(a) and 6(b) shows scanning electron micrograph offlexural fractured.

Figure 6: Chemical prepara-tion

Figure 7: Fibers immersed insolution

5 Conclusion

Based on the study of mechanical properties of five different naturalfiber reinforced hybrid composites, the following conclusions can bedrawn:

• In this work, three mechanical properties such as tensile strength,impact strength and flexural strength were analyzed and com-pared.

• The tensile strength of the flax/kenaf/epoxy hybrid compositeis increased by 50.53%, 37.40%, 45.21% and 14.26% comparedto pineapple / sisal / epoxy, kenaf /sisal / epoxy, pineapple /kenaf / epoxy and flax / pineapple / epoxy hybrid compositesrespectively.

• The impact strength of the flax/kenaf/epoxy hybrid com-posite is increased by 70.27%, 65.78%, 46.51% and 14.54%compared to pineapple / sisal / epoxy, kenaf / sisal / epoxy,pineapple / kenaf / epoxy and flax / pineapple / epoxy hybridcomposites respectively.

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• The flexural strength of the flax/kenaf/epoxy hybrid compos-ite is increased by 58.42%, 4.80%, 7.23% and 156.7% com-pared to pineapple / sisal / epoxy, kenaf / sisal / epoxy,pineapple / kenaf / epoxy and flax / pineapple / epoxy hybridcomposites respectively.

• From the SEM micrograph of flexural fracture surface sam-ples, flax/kenaf/epoxy hybrid composite excellent bonding toepoxy resin than other hybrid composites.

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