effect of alkali treatment on mechanical …mechanical proper-ties as compared to the untreated...

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Int. J. Mech. Eng. & Rob. Res. 2014 S Somashekar and G C Shanthakumar, 2014

ISSN 2278 – 0149 www.ijmerr.com

Vol. 3, No. 4, October, 2014

© 2014 IJMERR. All Rights Reserved

Research Paper

EFFECT OF ALKALI TREATMENT ON MECHANICAL

PROPERTIES OF SISAL -REINFORCED EPOXY

POLYMER MATRIX COMPOSITE

S Somashekar1* and G C Shanthakumar1

*Corresponding Author: S Somashekar � [email protected]

The present paper investigates the effect of fibre content and alkali treatment on tensile, flexuraland impact properties of unidirectional Sisal fibre natural-fibre-reinforced epoxy compositeswhich are partially biodegradable. The reinforcement sisal fibre fibre was collected from thefoliage of locally available sisal bushes through the process of water retting and mechanicalextraction. Commonly encountered problem between fibre and matrix is poor adhesion in natural-fibre-reinforced composites. To overcome this problem, specific treatments (physical andchemical) were suggested for surface modification of fibres by investigators. Alkali treatment isone of the simple and effective surface modification technique which is commonly used innatural fibre composites. In the present study both untreated and alkali-treated fibres wereused as reinforcement in sisal epoxy composites and the tensile, flexural and impact propertieswere determined at different fibre contents. The alkali treatment is found to be effective inimproving the tensile and flexural properties while the impact strength decreased.

Keywords: Sisal fibre, Epoxy resin, Alkali treatment, Mechanical properties

1 Department of Mechanical Engineering, T. John Institute of Technology, Bangalore- 560 083, India.

INTRODUCTION

The increase in the application of plant fibresas reinforcement for polymeric substrates hasbeen stimulated by the environmental costof manufacturing energy-intensive, syntheticfibres such as glass, carbon and kevlar.However, whereas synthetic fibres can beproduced with engineered properties to suitparticular applications this is not the case withnaturally occurring plant fibres. Properties ofthe cellulose fibres depend mainly on the

nature of the plant, locality in which it isgrown, age of the plant and extraction methodused. Today polymer composites are usedfor a wide range of applications. However,they do not undergo biodegradation easily,resulting in generation of solid waste, whichcauses environmental pollution. To meet thischallenge, researchers are focusing theirattention on producing bio-degradablecomposites with natural fibres/fabrics. Suchcomposites are termed as green composites.

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L Y Mwaikambo, 1999) studied the effect ofchemical treatment on sisal, Jute, hemp,Kapok etc., several green composites Shinet al., 1989) investigated the mechanicalproperties of bamboo-epoxy composites.Joseph et al., 2002) developed phenolformaldehyde com-posites reinforced withbanana fibres and pineapple leaf fibrereinforced polyethylene composites havebeen de-veloped by George et al., 1998).Gomes et al., 2004) inves-tigated theinfluence of Alkali treatment on tensileproperties of curaua fibre green composite.

Natural fibre composites are not onlybiodegradable and renewable but alsopossess several other advantages such aslightweight, low cost, high specific strength,high modulus, reduced tool wear and safemanufacturing pro-cess when compared withsynthetic fibre composites .Nowadayspolymer composite are used in construction,sports and recreational activities. Most of theparts of the automobiles, like door panels,trunk liners, seal backs, packages, speakertrays, engine and transmission covers, aremade using natural fibre composites.

Despite several advantages they alsopossess few limitations such as poorwettability, poor adhesion incompatibility withsome poly-meric matrices and high moistureabsorption by the fibres (Batchiar et al.,2008). The greatest challenge in using thenatural fibre as reinforcement in polymermatrix is the poor adhesion between naturalfibre and matrix resulting in inferior strengthof the composites. The main reason for thepoor compatibility is that while polymer matrixis hydrophobic and non-polar, the naturalfibres are hydrophilic and have polar groups

in their structure. Moreover, natural fibresconsist of several elementary fibresassociated with cellulose, hemicellulose, pec-tin, lignin, etc. The mechanical properties ofplant fibres are largely related to the amountof cellulose, which is closely associated withthe crystallinity of the fibre and the micro-fibrilangle with respect to the main fibre axis(Sreekala et al., 1997). Fibres with highcrystallinity and/or cellulose content havebeen found to possess superior mechanicalproperties Hence, they can not be consideredas the mono-filament fibres. To remove theunwanted elements from the fibre, specifictreatments are necessary. Many investigatorsfound and reported that the interfacialbonding can be enhanced by the surfacemodification of the fibre through alkalitreatment and treatment with couplingagents, which in turn will enhance the overallper- Over synthetic composites. (AlexandreGomes, 2004) studied the effect of alkalitreatment on curaua fibres composites andreported improvement in tensile strength andfracture strain. Huda et al., 2008), in theirinvestigation, pointed out that surface treatedfibre-reinforced composites shown superiormechanical proper-ties as compared to theuntreated fibre-reinforced composites.(Bisanda and Ansell., 1991) studied the effectof silanes on mechanical properties of sisal-epoxy composites and found considerableenhancement in compressive strength. (L YMwaikambo and M P Ansell, 1999) thoughMercerisation and acetylation, havesuccessfully modified the structure of naturalfibres and these modifications resulted inimproved performance of natural fibrecomposites by promoting better fibre to resinbonding.

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(Theepopnatkul et al., 2009), Hildegardiafabric (Guduri et al., 2006) and oil palm fibres(Sreekala and Thomas, 2003). Valadez-Gonzalez et al., 1999) investigated the effectof fibre surface treatment on the fibre-matrixbond strength of natural fibre-reinforcedcomposites and reported improvement inbond strength.

In the present study, sisal fibres are usedas reinforcement. They are very-low-densityfibres whose extraction from sisal fibres bushis very simple as its gum present in the sheathdissolves easily. The process is Economicallyfeasible. sisal fibres are widely used inpackaging and for making biodegradble bagsdue to their high strength and rigidity. In olderreferences the genus of the tree was referredto as Oreodoxa. These bushes are normallyfound in all parts of india,Europe and northamerica, Central and South America,.Someof the basic properties of this fibre wereinvesti-gated by (L YMwaikambo and M PAnsell et al., 2007). Epoxy was used as thematrix material in the present study. The roleof the matrix is to keep the fibres in a desiredlocation, orientation and to effectively transferthe stress to fibres. And also they protect thefibres from mechanical and chemicaldamage. Epoxy is most commonly usedmatrix material because of its desirableproperties like high strength, low viscosity,low flow rate, low volatility during cure, lowshrink rate, etc. The fibre-matrix inter-faceplays a vital role in the transformation of load,from the matrix to the fibre. Even thoughmechanical properties of the natural fibresare much lower than those of synthetic fibressuch as carbon, aramid, glass, etc., theirspecific properties, especially stiffness, are

comparable. Natural fibres are very light inweight in comparison with the synthetic fibres.Most of the natural fibres are nearly 50%lighter than glass.

The present work investigated the effectof fibre con-tent in weight percentage andalkali treatment (with NaOH) on tensile,flexural and impact properties of sisal naturalfibre-epoxy composites.

EXPERIMENTAL PROCEDURE

Materials

The matrix system used is an epoxy resin(Lapox-12) and hardener (k-8) supplied byAtul Limited, Gujarat, India. Lapox-12 is aliquid, unmodified epoxy resin of mediumviscosity. Hardener k8 is a low-viscosityroom-temperature curing liquid. It is generallypreferred in hand-lay-up applications. Beingreactive, it gives a short pot life and rapidcure at normal ambient temperatures. Thereinforcement is a sisal fibre, which wascollected from the foliage of locally availablesisal bush through the water retting andmechanical extraction.

Fibre Extraction

From the foliage sheath, the leaves and leafstem were removed and the sheath is driedfor 2 days in shade. In the next step, it wasimmersed in water retting tank for 2 weeks,followed by hand rubbing and rinsing in watertill the unwanted greasy material wasdissolved and fine fibre was extracted. Finally,the extracted fibre once again washedthoroughly in plenty of clean water to removethe surplus waste. Continuous fibre wasobtained with length up to 1.5 m. Theobtained fibre was dried under sun for 6 days.

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The average diameter of the fibre used forthe composite preparation was between 0.2and 0.3 mm. It contained Sisal Cellulose(wt%) 67-78, Lignin(wt%) 8-11, Hemicellulose(wt%) 10.0-14.2, Pectin (wt%) 10.0, Wax(wt%) 2.0, Moisture content(wt%) 11.0.

Alkali Treatment

Reinforcing fibers can be modified by physicaland chemical methods. Physical methods,such as stretching, calandering, thermotreatment, and the production of hybrid yarnsdo not change the chemical composition ofthe fibers. The dry fibre was treated with 5%solution of NaOH for 2 h to remove theunwanted soluble cellulose, pectin, lignin, etc.from the fibre. The fibre to solution weightratio was maintained at 1 : 20. After 2 h thefibre was washed thoroughly in distilled watercontaining 1% acetic acid to neutralise andremove excess amount of NaOH and driedat 50°C for 20 h. The fibres are dried toremove free water and placed in a glasscontainer in a conditioning chamber.

Chemical Analysis for Alpha (α)-

Cellulose

Chemical analysis was done for thedetermination of cellulose as per Indianstandards (IS: 6213, PART III-1971) with17.5% and 8.3% (by weight) sodiumhydroxide reagents. The residual high-molecular-weight fraction was left behindwhen a mixture of fibre and 8.3% NaOHsolution is filtered after the fibres have beeninitially swollen in a 17.5% NaOH solution.The residue was washed with distilled waterfollowed by acetic acid solution at 20°C andsoaked for 5 min. Again, it was washed withthe distilled water to free it from the acetic

acid and dried in the oven at 15°C. Nextcontents were transferred to a weighing bowland dried to a constant weight.

% alpha ( )-cellulose can be calculated asfollows:

x = 100a/m,

where x = % alpha ( )-cellulose by weight;a = weight of precipitate in grams; m = weightof fibre in grams calcu-lated on oven drybasis.

Composite Preparation

The mould box was made with the dimensionof 180 mm (L) 130 mm (W) 3.0 (T) mm. Therequired equipment for making the mould forhand-lay-up process were glass, sticker,spacer frames and a transparent plastic filmto keep on the top of the uncured compositebefore it was closed and compressed. Thetreated and untreated fibres were cutaccording to the mould size. Then, the matrixwas prepared by mixing the hardener toepoxy. The epoxy and hardener ratio wasmaintained at 12 : 1. To get the well-curedand a standard-quality specimen, the epoxyand hardener is mixed smoothly and slowlyfor approximately 8 min. Initial layer of themould was filled with epoxy resin mixture andthen the appropriate quantity of fibres wasplaced such that epoxy mixture is completelyspread over the fibres. Again, epoxy mixtureis poured on the fibre. Thus, the starting andending of the layers were of epoxy resin. Theplastic releasing film was placed on the topof the uncured mixture. Before applyingcompression, efforts were made to removeall bubbles with roller. Finally, thecompression pressure was applied uniformlyto achieve the uniform thickness of 3 mm and

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cured for 24 h at room temperature. Theobtained composite laminates are of the size180 130 3 mm3.

Testing of the Composites

The composite specimens were tested as perASTM standards. Tensile testing was doneas per ASTM D 3039-76 with the help of FIE-model Universal Testing Machine at acrosshead speed of 10 mm/min. Thetemperature was conditioned at 24°C with thehumidity of 50%. The specimen dimensionswere 150 15 3 mm3. Flexural testing wasdone as per ASTM D 5943-96 standardsusing three point bending method at a cross-head speed of 5 mm/min and at atemperature of 24 C with the humidity of 50%.The specimen dimensions were 100 15 3 mm3. The impact testing was done as per ASTMD 256-88 by Izod impact machine withunnotched specimen. The specimendimensions were 120 12. 2 mm3. In eachcase, eight samples were tested and theaverage values were reported.

RESULTS AND DISCUSSION

Tensile strength, tensile modulus and %elongation at break of untreated sisal fibre(UTRF)-reinforced and alkali-treated sisalfibre (ATRF)-reinforced composites werepresented in table 1 at different fibre contents(5, 10, 15 and 20% wt.). For correctunderstanding of the effect of fibre contenton tensile strength, ten-sile modulus andpercentage elongation at break separatecharts have been plotted for untreated andalkali-treated types of composites as shownin figures 1-3, respectively. From Figures 1-3, it is evident that fibre content is directlyproportional to tensile strength, tensilemodulus and percentage elongation at

Figure 1: The Effect of Fibre Content onTensile Strength of Untreated and

Alkali-treated Composites

Figure 2: The Effect of Fibre Content onTensile Modulus of Untreated and


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Type of composite

Epoxy without reinforcement

UTRF

ATRF

Table 1: Tensile Properties of Untreated and Treated Composites at Different Fibre Contents

Fibre content(% wt.)

0

05

10

15

20

05

10

15

20

Tensile strength(MPa)

32.5

15.34

19.47

34.47

38.89

16.78

21.29

36.56

42.29

Tensile modulus(MPa)

1800.00

980.95

1178.60

1289.76

1957.31

1149.87

1356.72

1442.71

2131.69

Elongation atbreak (%)

1.6

2.37

3.30

3.39

3.82

2.49

3.51

3.71

3.92

Type of composite


UTRF

ATRF

Table 2: Flexural Properties of Untreated and Treated Composites at Various Fibre Contents


0

05

10

15

20

05

10

15

20

Flexural strength(MPa)

39.00

33.423

42.828

44.187

57.655

34.808

47.243

52.052

62.677

Flexural modulus(MPa)

3507.40

3705.18

3997.78

4158.25

4568.25

4550.80

4790.02

4910.00

4945.00

Figure 3: The Effect of Fibre Content on% Elongation at Break of Untreated

and Alkali-treated Composites

Figure 4: The Effect of Fibre Content onFlexural Strength of Untreated and


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break for both treated and untreated fibrecomposites and peak value is at 20% fibrecontent. When com-pared with the untreatedfibre composites, the alkali-treated fibre com-posites recorded 8% increase in tensilestrength, 8.2% increase in tensile modulusand 2.6% increase in percentage elongationat break is at 20% fibre content.

Flexural properties of untreated and

treated composites at various fibre contentswere shown in Table 2 and separate chartsfor flexural strength and flexural modulus aredepicted in Figures 4 and 5. From the figuresit can be seen that fibre, content, is directlyproportional to flexural strength and flexuralmodulus for both treated and untreated fibrecomposite and peak value is at 20% fibrecontent.

Type of composite


UTRF

ATRF

Table 3: Impact Strength of Untreated and Treated Composites at Various Fibre Contents


0

05

10

15

20

05

10

15

20

Impact strength(J/m)

30.6

74.36

92.35

116.52

148.94

69.32

87.94

98.06

116.43

Figure 5: The Effect of Fibre Content onFlexural Modulus of Untreated and


Figure 6: The Effect of Fibre Content onImpact Strength of Untreated and


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untreated fibre composites, the alkali-treated fibre com-posites recorded 8%increase in flexural strength and 7.7%increase in flexural modulus at 20% fibrecontent. This increase in tensile and flexuralproperties of alkali-treated fibre compositescould be due to the increased interfacebetween matrix and fibre after treatment. Thisis evidenced by the fracture morphology oftensile and flex-ural composites before andafter alkali treatment as shown in the figures7a-d. The fibre damage is more in untreatedfibre-reinforced composites when comparedwith the alkali-treated fibre-reinforcedcomposites. The alkali treatment by removinghemicellulose and lignin contents from thefibre yields the higher percentage of (alpha)cellulose in natural fibres Jayaramudu et al(2009). Chemical analysis revealed that afteralkali treatment, the percentage of -celluloseof Roystonea regia fibre increased from 58to 65%. This will render the fibre surfacecoarser, leading to better interface betweenmatrix and fibre. Alkalization also causesfibril-lation, i.e. breaking of fibre bundles into smaller fibres, which would increase theeffective surface area available for wettingby the matrix material (Yan et al., 2000). Afterfibrillation due to the reduced diameter of thefibre, the aspect ratio of the fibre increasesand yields rough surface topography, whichin turn offers a better fibre-matrix interface.This results in obtaining the enhanced proper-ties. The effect of alkali treatment in modifyingsurface of fibre can be observed by scanningelectron microscopy (SEM) as shown in theFigures 8a and b. The alkali-treated fibre hasbecome coarser (see Figure 8b) whencompared with the untreated fibre (see Figure8a).

Izod impact test results were reported intable 3 for untreated and alkali-treatedcomposites at various fibre contents and thecorresponding chart was shown in the Figure6. From the figure it is evident that althoughthere is an increase in impact strength withincrease in fibre loading, the values weredecreased after alkali treatment and, at 20%fibre loading, the impact strength was de-creased by 22%. This could be mainly dueto the reason that during the impactconsiderable part of energy absorp-tion takesplace through the fibre pull-out process, butafter alkali treatment, due to the removal ofsoluble greasy contents from the fibre, strongmechanical interlocking develops betweenfibre and matrix, and fibre pull-out isminimized. This, in turn, will decrease theimpact strength.

Figure 7: (a) Tensile Fractured Surface ofUntreated Composite (20% Fibre Content).(b) Tensile Frac-tured Surface of Alkali-treated Composite (20% Fibre Content).(c ) Flexural Fractured Surface of UntreatedComposite (20% Fibre Content). (d)Flexural Fractured Surface of Alkali-treatedComposite (20% Fibre Content)

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Figure 8: (a) Untreated Fibre Surface.(b) Alkali-treated Fibre Surface

CONCLUSION

Tensile strength, tensile modulus andpercentage of elonga-tion of untreated andalkali-treated sisal natural fibre-reinforcedepoxy composites were increased withincrease in fibre content and are highest at20% wt. fibre content. Alkali-treated fibrecomposites have shown superior tensileproperties than untreated composites. Alsoflexural strength and flexural modulus ofuntreated and alkali-treated fibre compositeswere increased with increase in fibre contentand are highest at 20% wt. fibre content.Alkali-treated composites have shownsuperior flexural properties than untreatedfibre composites. For both untreated andalkali-treated fibre composites, there is anincrease in impact strength with increase infibre con-tent and found to be highest at 20%wt. fibre content. But, the impact strength ofalkali-treated fibre composites wasdecreased at all fibre contents whencompared with the untreated fibrecomposites. Study demonstrated that sisalnatural-fibre-reinforced epoxy compo-sites

could be successfully produced with goodmechanical properties and the tensile andflexural properties can be further enhancedby alkali treatment. This study also revealsthat maximum strength and maximumtoughness cannot be achieved simul-taneously and optimum combinations ofdesired mechanical properties are possibleonly through careful design of composites.

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effect of alkali treatment on mechanical …mechanical proper-ties as compared to the untreated...

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