Short sisal fiber reinforced polypropylene composites: the role of interface modification on...

This article was downloaded by: [Acadia University]On: 02 May 2013, At: 05:53Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK

Composite InterfacesPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/tcoi20

Short sisal fiber reinforcedpolypropylene composites:the role of interfacemodification on ultimatepropertiesP. V. Joseph , Kuruvilla Joseph & Sabu ThomasPublished online: 02 Apr 2012.

To cite this article: P. V. Joseph , Kuruvilla Joseph & Sabu Thomas (2002): Shortsisal fiber reinforced polypropylene composites: the role of interface modificationon ultimate properties , Composite Interfaces, 9:2, 171-205

To link to this article: http://dx.doi.org/10.1163/156855402760116094

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private studypurposes. Any substantial or systematic reproduction, redistribution,reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make anyrepresentation that the contents will be complete or accurate or up todate. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall notbe liable for any loss, actions, claims, proceedings, demand, or costs or

http://www.tandfonline.com/loi/tcoi20

http://dx.doi.org/10.1163/156855402760116094

http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/page/terms-and-conditions

damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3

Composite Interfaces, Vol. 9, No. 2, pp. 171–205 (2002)Ó VSP 2002.

Short sisal � ber reinforced polypropylene composites:the role of interface modi� cation on ultimate properties

P. V. JOSEPH 1, KURUVILLA JOSEPH 1 and SABU THOMAS 2;¤

1 Post-graduateDepartment of Chemistry, St. Berchmans’ College Changanacherry, Kottayam,Kerala, India

2 School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India

Received 22 May 2000; accepted 23 April 2001

Abstract—Sisal � bers have been used for the reinforcementof polypropylenematrix. The compatibi-lization between the hydrophilic cellulose � ber and hydrophobic PP has been achieved through treat-ment of cellulose � bers with sodium hydroxide, isocyanates, maleic anhydride modi� ed polypropy-lene (MAPP), benzyl chloride and by using permanganate. Various � ber treatments enhanced thetensile properties of the composites considerably, but to varying degrees. The SEM photomicrographsof fracture surfaces of the treated composites clearly indicated the extent of � ber–matrix interfaceadhesion, � ber pullout and � ber surface topography. Surface � brillation is found to occur during al-kali treatment which improves interfacial adhesion between the � ber and PP matrix. The grafting ofthe � bers by MAPP enhances the tensile strength of the resulting composite. It has been found thatthe urethane derivative of polypropylene glycol and cardanol treatments reduced the hydrophilic na-ture of sisal � ber and thereby enhanced the tensile properties of the sisal–PP composites, as evidentfrom the SEM photomicrographs of the fracture surface. The IR spectrum of the urethane derivativeof polypropylene glycol gave evidence for the existence of a urethane linkage. Benzoylation of the� ber improves the adhesion of the � ber to the PP matrix. The benzoylated � ber was analyzed by IRspectroscopy. Experimental results indicated a better compatibilitybetween benzoylated � ber and PP.The observed enhancement in tensile properties of permanganate-treated composites at a low con-centration is due to the permanganate-induced grafting of PP on to sisal � bers. Among the varioustreatments, MAPP treatment gave superior mechanical properties. Finally, experimental results of themechanical properties of the composite have been compared with theoretical predictions.

Keywords: Mechanical properties; chemical treatments; sisal–PP composites.

1. INTRODUCTION

Considerable efforts have been made in recent years to � nd light, strong and inex-pensive reinforcing � bers in order to reduce the cost of polymeric materials while at

¤To whom correspondence should be addressed.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3

172 P. V. Joseph et al.

the same time improving the mechanical performance. Cellulose � bers, which orig-inate from a renewable and common source, have properties that make them uniqueas inexpensive reinforcement [1]. Wood cellulose � bers have successfully been usedas reinforcement of polyole� nes [2–4]. Cellulosic � bers like sisal, pineapple, etc.have also been evaluated as reinforcements [5–8]. When cellulose � ber is used asreinforcement of polyole� nes, there is a lack of interfacial adhesion between thepolyole� ne matrix and the cellulose phase. A major disadvantage of the cellulose� bers is their highly polar nature which makes them incompatible with non-polarpolymers such as commodity thermoplastics [9]. This situation calls for the devel-opment of strategies for the surface modi� cation of cellulose surfaces, so as to havean effective control over the � ber/polymer interface.

The stress transfer at the interface between two different interphases is determinedby the degree of adhesion. A strong adhesion at the interface is needed for aneffective transfer of stress and load distribution throughout the interface [10]. Thisdemands surface treatment capable of producing a good quality interface. Theinterface, or interlayer between reinforcing � bers and matrix is widely regardedas an important factor in determining the mechanical properties of compositematerials [11].

Natural � ber composites combine good mechanical properties with a low speci� cmass; but their high level of moisture absorption, poor wettability and insuf� cientadhesion between untreated � bers and the polymer matrix leads to debondingwith age [12, 13]. In order to improve the wettability and thus the adhesion ofthe � bers by the matrix, a coupling or compatibilizing agent is deposited on the� ber or eventually reacted with the � ber, leading to an interface or interphaseof high adhesion [14–18], capable of inducing physical and chemical bondsbetween the � ber and matrix. The lack of interfacial interactions leads to internalstrains, porosity and environmental degradation [19]. To improve the propertiesof the composites, the natural reinforcing � bers can be modi� ed by physical andchemical methods. Physical methods such as stretching [20], calendering [21, 22],thermotreatment [23], electronic discharge (corona, cold plasma) [24] and theproduction of hybrid yarns [25, 26], do not change the chemical composition orstructure but only surface properties of the � ber.

The most important chemical modi� cation involves coupling methods. The cou-pling agent used contains chemical groups that can react with the � ber and the poly-mer. The bonds formed are covalent or hydrogen bonds which improve the interfa-cial adhesion. Kokta and coworkers [27–30] have reported that coupling agents likesilanes and isocyanates improve the mechanical properties and dimensional stabil-ity of cellulose � ber–PE composites. Peroxide induced adhesion in cellulose � berreinforced thermoplastic composites has attracted the attention of various workersdue to the easy processability and improvement in mechanical properties [31–35].Potassium permanganate has been reported by Tripathy et al. [36] and Moharanaet al. [37] to be a powerful initiator for grafting of methyl methacrylate onto jute

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3

Short sisal � ber reinforced polypropylene composites 173

� ber. Reports of grafting of dicarboxylic anhydrides on to polyole� nes and its useas compatibilizer have appeared in the literature [38–41].

In this paper, attempts have been made to study the effects of various chemi-cal treatments such as use of sodium hydroxide, polypropyleneglycol derivative oftoluene diisocyanate (PPG-TDI), polymethylene polyphenyl isocyanate (PMPPIC)maleic anhydride, maleic anhydride modi� ed polypropylene (MAPP), or benzoy-lation and permanganate on the mechanical properties of sisal � ber-polypropylenecomposites.

2. EXPERIMENTAL

2.1. Materials

Isotactic polypropylene (Koylene M3060) was supplied by IPCL, Baroda. Sisal� ber (Agave Sisalana) was obtained from local sources. The physical and mechani-cal properties of PP and sisal � ber are given in Table 1. The � ber was washed thor-oughly with water and dried in an air oven at 80±C for 6 h, before being chopped intothe desired length of 6 mm for � ber treatment and the preparation of the composites.

Toluene-2,4-diisocyanate (TDI), poly[methylene poly(phenyl isocyanate)] (PMP-PIC), polypropylene glycol (PPG) of molecular weight 1000 were supplied byAldrich Chemical Company, USA. Dicumyl peroxide (DCP) (Varox DCP-R) wassupplied by R. T. Vanderbilt Co., Norwalk, USA. Cardanol, the principal componentof cashew nut shell liquid (CNSL) obtained from Anacardium occidentale L., is aplant-source raw material abundant in tropical countries like India (Southern part)and Vietnam. Cardanol was supplied by Satya Chemicals, Chennai. Dibutyl tindilaurate was obtained from Scienti� c and Industrial Supplies Corporation, Mum-bai. Maleic anhydride (BDH sample) was supplied by Citra Chemicals, Ernakulam.Potassium permanganate, sodium hydroxide, maleic anhydride and benzoyl chlo-ride used in the present study were of chemically pure grade.

Table 1.Physical and mechanical properties of PP and sisal � ber

Properties PP Sisal � ber

Melt � ow index (g/10 min) 3 —Density (g/ cm3) 0.9 1.45Cellulose content (%) — 85–88Lignin content (%) — 4–5Tensile strength (MPa) 35 400–700Tensile modulus (MPa) 498 9000–20 000Elongation at break (%) 10.33 5–14

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


2.2. Fiber treatment

2.2.1. Alkali treatment. The chopped � bers were taken in a stainless steel vessel.A 10% solution of NaOH was added into the vessel and stirred well. This was keptfor 1 h with subsequent stirring. The � bers were then washed thoroughly with waterto remove the excess of NaOH sticking to the � bers. Final washings were carriedout with distilled water containing little acetic acid. The � bers were then air dried.

2.2.2. PPG-TDI treatment.

2.2.2.1. Preparation of urethane derivative of polypropylene glycol (PPG) [7].The synthesis of the urethane derivative of PPG was carried out using a 1 : 5 molarratio of PPG and toluene diisocyanate (TDI) containing free isocyanate group. PPG(mol. wt. ¼ 1000) in chloroform was taken in a round bottomed � ask (500 ml)and 1 ml dibutyl tin dilaurate was added as catalyst. The � ask was immersed in awaterbath kept at 70±C. A 20% solution of TDI in CHCl3 was taken in a pressureequalizing funnel. Then TDI was added drop-wise into PPG under constant stirringuntil the addition of TDI was complete. The stirring was continued for one morehour for the completion of the reaction. The product formed contained one freeisocyanate group for further reaction as shown in Scheme 1. The product obtainedwas used as such for further reaction.

Treatment of sisal � ber with urethane derivative of PPG. The alkali treatedor untreated � bers were placed in a round bottomed � ask and soaked with anappropriate volume of CHCl3 and a little dibutyl tin dilaurate as catalyst. The� ask was then immersed in a water bath at 70±C. The round bottomed � ask was� tted with a pressure equalizing funnel containing the urethane derivative. Theurethane derivative was added into the � ask drop-wise with suf� cient stirring. After

Scheme 1. The reaction pathway for the preparation of the urethane derivative of polypropyleneglycol.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Scheme 2. A possible reaction between the free isocyanate groups in the urethane derivative of PPGand cellulosic sisal � ber.

the complete addition of urethane, the reaction was allowed to continue for onemore hour. The urethane treated � bers were puri� ed by re� uxing with acetone for8 h in a soxhlet extraction apparatus followed by repeated washings with distilledwater. Finally, the � bers were oven dried at 80±C. A possible reaction between thefree isocyanate groups in urethane derivative of PPG and cellulosic sisal � ber isshown in Scheme 2.

2.2.2.2. Preparation of urethane derivative of cardanol. The preparation of theurethane derivative of cardanol as reported elsewhere [35] was carried out using a1 : 1 molar ratio of cardanol and TDI containing a free isocyanate group. Cardanol(30 g, 0.1 mol) was taken in a pressure equalizing funnel and diluted with 50 mlchloroform (distilled) and 1 ml dibutyl tin dilaurate added as catalyst. TDI (17.4 g,0.1 mol) was taken in a round bottomed � ask (500 ml). The cardanol solution wasadded dropwise into TDI under constant stirring until the addition of cardanol wascomplete. The stirring was continued for one more hour for the completion of thereaction. The product formed contained one free isocyanate group which was usedfor further reaction (Scheme 3).

Treatment of sisal � ber with urethane derivative of cardanol. The alkali treateddried � bers were placed in a round bottomed � ask and soaked with an appropriatevolume of CHCl3 and a little (1 ml) dibutyl tin dilaurate catalyst. The roundbottomed � ask was � tted with a pressure equalizing funnel containing the urethanederivative. The urethane derivative was added into the � ask dropwise with suf� cient

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Scheme 3. The reaction pathway for the preparation of the urethane derivative of cardanol.

stirring. After the complete addition of urethane, the reaction was allowed tocontinue for one more hour (Scheme 4). The urethane treated � bers were puri� ed byre� uxing with acetone for 8 h in a Soxhlet apparatus followed by repeated washingwith distilled water. Finally, the � bers were oven dried at 80±C.

2.2.3. PMPPIC treatment. To the sisal � bers dipped in chloroform (distilled) ina 500 ml RB � ask, varying percentages of PMPPIC (5 to 12% by weight of � ber)in chloroform (50 ml) was added from a pressure equalizing funnel. The additioncontinued for 30 min and the contents stirred using a magnetic stirrer. The wholeassembly was immersed in a water bath at 70±C before the addition of PMPPIC.After the complete addition of PMPPIC, the reaction was allowed to continue for2 h more. The urethane modi� ed � bers were collected.

2.2.4. Maleic anhydride treatment. Maleic anhydride treatment was carried outby two methods.

Method 1, To a melt of polypropylene in the Haake Rheocord, at 170±C and at50 rpm, DCP (1 part) was added and mixed for 2 min and then maleic anhydride(3 to 12% by � ber weight) was introduced and mixed for another 2 min. To thissisal � ber was added and the mixing continued for another 6 min more.

Method 2, Preparation of maleic anhydride modi� ed polypropylene (MA-PP):Maleic anhydride modi� ed PP as reported elsewhere [42] was prepared by meltmixing PP with maleic anhydride (5 parts), benzoquinone (0.75 parts) and dicumyl

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Scheme 4. A possible reaction between the free isocyanate group in the urethane derivative ofcardanol and cellulosic sisal � ber.

Scheme 5. The mechanism for formation of MAPP.

peroxide (3 parts) in a Haake Rheocord at a temperature of 170±C at 50 rpm for10 min. In the MAPP, maleic anhydride groups are grafted on to the PP chainbackbone as shown in Scheme 5.

The grafting of MA-PP on to the sisal � bers was performed as follows. To amelt of PP in the Haake Rheocord at 170±C and at 50 rpm sisal � ber was added(20%), followed by the addition of MA-PP in varying amounts (5 to 15 parts) andthe mixing was performed for 10 min.

2.2.5. Benzoyl chloride treatment (benzoylation). A � xed amount (35 g) ofwashed � ber as reported elsewhere [8] was soaked in 10% NaOH for 1 h, � lteredand washed with water. The treated � ber was suspended in 10% NaOH solutionand agitated well with 50 ml benzoyl chloride. The mixture was kept for 15 min,

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


� ltered, washed thoroughly with water, and dried between � lter paper. The isolated� ber was then soaked in ethanol for 1 h to remove the unreacted benzoyl chlorideand � nally was washed with water and dried.

2.2.6. Permanganate treatment. Sisal � bers were soaked for 2 min in KMnO4

solution (in acetone) of various concentrations. These � bers were then decantedand dried in air.

2.2.7. Preparation of PP–sisal composites. The PP–sisal composites wereprepared by the melt mixing method. In this method, the � ber was added to amelt of polypropylene and mixing was performed in a Haake Rheocord mixerat a temperature of 170±C and a rotor speed of 50 rpm for 10 min durationas reported elsewhere [7]. The mix was taken from the mixer while hot andthen subjected to sheeting in a two roll mill. Rectangular specimens measuring150 £ 150 £ 2:5 mm3 were prepared by compression molding at a pressure about8 MPa and at a temperature of 170±C. It was then cut to specimens measuring120 £ 12:5 £ 2:5 mm3.

2.2.8. Mechanical testing. Tensile testing of rectangular specimens of size120£ 12:5 £ 2:5 mm3 was carried out using electronic tensile testing machine TNEseries 9200 at a cross-head speed of 50 mm min¡1 and a gauge length of 50 mm.The tensile modulus and elongation at break of the composites were calculated fromthe load–displacement curve. At least � ve specimens were tested for each set ofsamples and the mean values were reported.

2.3. IR spectroscopy

A Shimadzu IR-490 spectrophotometer was used to analyze the changes in chemicalstructure of treated and untreated sisal � ber. Powdered � ber pelletized withpotassium bromide was used for recording the spectra.

3. RESULTS AND DISCUSSION

3.1. Effect of alkali treatment

Table 2 shows the variation in tensile properties of sisal –PP composites (bothuntreated and alkali treated) with different � ber loading. It is evident from the tablethat there is an enhancement in tensile strength and modulus with � ber loading,i.e. the alkali-treated composites showed superior tensile properties compared withuntreated composites. This is due to the fact that alkali treatment improves the� ber surface adhesive characteristics by removing natural and arti� cial impurities,thereby producing a rough surface topography [35]. It may be noted that the � bersbecome thinner upon alkali treatment. This may be due to the dissolution and

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Table 2.Variation of tensile properties of alkali treated sisal � ber-PP composites with � ber content (� berlength: 6 mm)

Fiber Tensile Standard Modulus Standard Elongation Standardcontent strength deviation (MPa) deviation at break deviation(%) (MPa) (%)

0 35 0.641 498 0.707 10.3 0.36510 36.5 (35.6) 0.5 (0.351) 958 (578) 0.568 (0.8) 9.1 (9.1) 0.753 (0.115)20 40.35 (36.5) 0.507 (0.252) 1094 (680) 1.25 (0.586) 8.67 (8.3) 0.335 (0.075)30 44.35 (37) 0.634 (0.361) 1194 (735) 0.764 (0.436) 7.4 (8.0) 0.579 (0.252)

Values given in parentheses are those of untreated composites.

leaching of fatty acids and some of the lignin component of the � ber. As a result,the surface of the � ber becomes rough. Figures 1a and 1b are SEM photographs ofthe surface of untreated and alkali treated sisal � ber, respectively. The treated � berhas a rough surface topography. This will promote mechanical anchoring between� ber and matrix, which is schematically presented in Fig. 2. In other words, alkalitreatment reduces � ber diameter and thereby increases the aspect ratio. Therefore,the development of a rough surface topography and increase in aspect ratio givebetter � ber–matrix interface adhesion and an increase in mechanical properties.

Figure 3 shows the IR spectrum of sisal � ber: (a) untreated and (b) NaOHtreated. The characteristic feature of IR spectrum of sisal � ber is due to thelignin and hemicellulose components that exist in � bers. From the IR spectrum(Fig. 3a), the following peaks have been observed. The strong broad peak at3300–3400 cm¡1 in the spectrum of sisal � ber is the characteristic hydrogen bonded

OH stretching vibrations. The strong peak at 2900 cm¡1 is due to CH stretchingvibrations [43]. The peak at 1730 cm¡1 is the characteristic band for carbonyl( C O) stretching. With the alkali treatment this band disappears (Fig. 3b). Itappears that in alkali treatment a substantial portion of uranic acid, a constituent ofhemicellulose xylan, is removed resulting in the disappearance of this peak. Theband near 1420 cm¡1 is assigned to the CH2 symmetrical deformation. Thebands at 1370, 1330 and 1310 cm¡1 are due to CH deformation, OH in-planebending and CH2 wagging respectively. The band near 1245 cm¡1 is due to the

C O C band in the cellulose chain. The peak near 900 cm¡1 is characteristicof ¯-linkages.

3.2. Effect of TDI-PPG treatment

The cellulose hydroxyl groups in the � ber are relatively unreactive, since they formstrong hydrogen bonds. Alkali treatments may destroy the hydrogen bonding incellulose hydroxyl groups, thereby making them more reactive [42, 44]. Thisfacilitates the reaction between the alkali treated � ber and the isocyanate groupin TDI. The possible reaction between the free isocyanate group in the urethanederivative of PPG and cellulose is illustrated in Scheme 2. The linking of the

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


(a)

(b)

Figure 1. SEM photographs of (a) the surface of untreated sisal � ber (£400) and (b) the surface ofalkali treated sisal � ber (£400).

isocyanate (TDI) to the cellulose is through strong covalent bonds and forms aurethane linkage.

R N C O C H O Cellulose ¡! R

H O

N C O Cellulose (1)

The IR spectrum of untreated and isocyanate (urethane derivative of PPG) mod-i� ed � ber is shown in Figs 3a and 4, respectively. Emergence of bands near

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 2. A schematic picture showing better adhesion between PP and sisal � ber during alkalitreatment.

1700 cm¡1 ( C O stretching) 1538 cm¡1 ( C N H stretching) and 1280 cm¡1

( N C O stretching) are typical of polyurethane segments [45]. SEM pho-tographs given in Figs 5a and 5b show the surface of urethane derivative of PPGand urethane derivative of cardanol-treated � ber PP composites. A clear coating ofurethane derivative on the � ber surface is evident from the � gure.

Figure 6 shows the effect of the variation of molar ratio of PPG to TDI on thetensile strength of sisal –PP (untreated � ber) composite at 20% � ber loading. Fromthe � gure it is clear that the tensile properties increases from 1 : 2 molar ratio to1 : 5 molar ratio of PPG : TDI and then a leveling off is observed. So for TDI-PPG treatment, 1 : 5 molar ratio of PPG : TDI is used. Table 3 shows the tensileproperties of the urethane derivative of PPG treated, urethane derivative of cardanoltreated, alkali treated and untreated sisal –PP composites having 30% � ber loading.It is found that the urethane derivative of cardanol and the urethane derivative ofPPG treated sisal –PP composite show superior mechanical properties comparedwith the alkali-treated and untreated sisal –PP composites. The long chain structureof urethane derivatives linked to the cellulosic � ber makes the � ber hydrophobic,compatible and highly dispersible in the PP matrix. This will result in a stronginterfacial bond between � ber and PP matrix. SEM photomicrograph given in Fig. 7shows the tensile fracture surface of the urethane derivative of PPG treated � ber PPcomposite. From the � gure, the better � ber–matrix adhesion between isocyanatetreated sisal � bers and PP matrix can be understood. This facilitates effectivestress transfer between the � ber and PP matrix. When the � ber surface is modi� edby a polymeric interphase, interdiffusion between PP and cellulosic � ber mightbe expected, leading to increased tensile strength of the composite. The longerthe chain of the modi� er, the larger are the tensile properties of the composites.The longer, � exible chain of urethane derivative of isocyanate is able to diffusemore deeply into the PP matrix and becomes involved more fully in interchainentanglements. This contributes to the enhanced mechanical performance of the

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


(a)

(b)

Figure 3. IR spectra of (a) untreated sisal � ber and (b) sodium hydroxide treated � ber.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 4. IR spectrum of the urethane derivative of PPG treated � ber.

Table 3.Variation of tensile properties of sisal–PP composites with � ber treatment (� ber length 6 mm and� ber content 30%)

Components Tensile Standard Modulus Standard Elongation Standardstrength deviation (MPa) deviation at break deviation(MPa) (%)

Untreated 37 0.361 735 0.436 8.3 0.252Alkali treated 44.35 0.643 1194 0.535 7.4 0.264Urethane derivative 49.8 0.436 1598 0.424 6.8 0.264of cardanol treated(NaOH washed � ber)Urethane derivative 51.2 0.361 1663 0.624 6.5 0.346of PPG treated(NaOH washed � ber)

system. The possible hypothetical chemical structure of cellulose � ber-urethanederivative of PPG-PP and cellulose � ber-urethane derivative of cardanol-PP in theinterfacial area are given in Fig. 8.

The improvement in the tensile properties of sisal � ber-urethane derivative ofPPG-PP composite over sisal � ber-urethane derivative of cardanol-PP composite isattributed to the presence of polypropylene structures in treated � ber similar to that

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


(a)

(b)

Figure 5. SEM photographs showing the surface of the urethane derivative of (a) PPG treated� ber/PP composites (£800) (� ber loading 20%, � ber length 6 mm), and (b) cardanol treated � ber/PPcomposites (£800) (� ber loading 20%, � ber length 6 mm).

of PP matrix, which improves the thermodynamic compatibility between PPGTDItreated � ber and PP matrix.

3.3. PMPPIC treatment

It has already been reported that poly[methylene(poly(phenyl isocyanate))] (PMP-PIC) treated cellulose � ber–polymer composites exhibit superior mechanical prop-erties and dimensional stability [28]. The functional group N C O in PMPPIC

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 6. The variation of molar ratio of PPG to TDI with the the tensile strength of sisal–PP(untreated � ber) composite at 20% � ber loading (� ber length 6 mm).

Figure 7. SEM photograph showing the tensile fracture surface of the urethane derivative of PPGtreated � ber/PP composite (£800) (� ber loading 20%).

is highly reactive to the OH groups of cellulose and lignin. This leads to thedevelopment of a urethane linkage through a strong covalent bond as representedbelow.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 8. The possible hypothetical chemical structures of the cellulose � ber/urethane derivative ofPPG-PP and cellulose � ber/urethane derivative of cardanol-PP in the interfacial area.

Figure 9. IR spectrum of PMPPIC modi� ed sisal � ber.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 10. The effect of PMPPIC concentrationon the tensile properties of PMPPIC treated sisal/PPcomposites at 20% � ber loading.

N C O C HO ¡!

H O

N C O (2)

The IR spectrum of untreated and PMPPIC modi� ed � ber is shown in Figs 3aand 9, respectively. On PMPPIC treatment, new bands appear in the spectrumat 1700, 1538 and 1280 cm¡1 corresponding to ( C O) stretching (C N H)stretching and N C O stretching respectively. Figure 10 represents the effectof PMPPIC concentration on the tensile properties of PMPPIC treated sisal /PPcomposites at 20% � ber loading. It is observed that PMPPIC treatment signi� cantlyimproves the performance of the composite. The SEM photomicrograph given inFig. 11 shows a clear coating of PMPPIC on the surface of sisal � ber. The two-step process (i.e. � bers are � rst coated with PMPPIC and then these coated � bersare retreated with PMPPIC during mixing of � ber and polypropylene) helps toincrease the interfacial area and hence mechanical properties. Tensile strength ofthe composite increases and reaches a maximum at 10% isocyanate concentrationand thereafter it decreases. Maximum modulus is observed at 10% concentrationand thereafter it remains almost a constant. At higher concentration, the unreactedisocyanate tends to decrease the tensile properties of the composite.

Table 4 shows the effect of PMPPIC (10% by weight of the � ber) treatment ontensile properties of sisal –PP composite at different � ber loadings. In all cases, asigni� cant increase in tensile properties is observed. The overall improvements in

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 11. SEM photograph showing the surface of PMPPIC treated � ber (£800).

Table 4.Effect of PMPPIC (10% by wt of � ber) treatment on tensile properties of sisal–PP composites atdifferent � ber loading (� ber length 6 mm)

Fiber Tensile Standard Modulus Standard Elongation Standardloading strength deviation (MPa) deviation at break deviation(wt%) (MPa) (%)

10 37.5 (35.6) 0.3 (0.351) 1022 (578) 1 (0.8) 8.6 (9.1) 0.2 (0.115)20 44.8 (36.5) 0.59 (0.252) 1425 (680) 0.529 (0.586) 7.8 (8.3) 0.494 (0.075)30 48.9 (37) 0.4 (0.361) 1591 (735) 0.7 (0.436) 6.4 (7.8) 0.4 (0.252)


mechanical properties due to the addition of isocyanates to composites indicate thatPMPPIC acts as a good coupling agent and improves interfacial contact between� ber and polymer. The long chain molecules present in PMPPIC interact with PPleading to van der Waals type of interactions. A possible hypothetical chemicalstructure of bonding of PMPPIC at the interfacial area of sisal � ber and PP isdepicted in Fig. 12.

As a result of coupling action, the hydrophilicity of the sisal � ber is reducedthereby favoring a good adhesion between the � ber and the matrix. The longerand � exible chain of PMPPIC is able to diffuse more deeply into the PP matrix,thereby favoring entanglements with the matrix. This contributes to the enhancedmechanical performance of the system. The wettability of polymer by � ber dependson the viscosity of the polymer and surface tension of both materials [46]. Forbetter wettability, the surface tension of the matrix should be lower than the surfacetension of the � ber. Due to coupling action, the adhesion improvement arises fromthe relatively high surface energy of the � ber.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 12. A possible hypothetical chemical structure of bonding of PMPPIC at the interfacial areaof sisal � ber and PP.

Figure 13. The effect of maleic anhydride concentration on tensile properties of sisal/PP compositeat 20% � ber loading.

3.4. Effect of maleic anhydride treatment

Figure 13 shows the effect of varying the concentration of maleic anhydride ontensile properties of sisal –PP composite at 20% � ber loading. It is clear from the� gure that there is an enhancement in strength and modulus values on increasingthe maleic anhydride concentration. Enhancement is maximum at a concentration

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 14. A hypothetical model of the interphase between MAPP with the cellulose OH of thesisal � ber.

Table 5.Effect of MA (9%) concentration on the mechanical properties of sisal–PP composite at different� ber loading

Loading Tensile Standard Modulus Standard Elongation Standard(%) strength deviation (MPa) deviation at break deviation

(MPa) (%)

0 35 0.641 498 0.707 10.3 0.36510 38.1 (35.6) 0.793 (0.351) 1090 (578) 0.808 (0.8) 8.9 (9.1) 0.397 (0.115)20 43.6 (36.5) 0.436 (0.252) 1465 (680) 0.436 (0.586) 7.66 (8.3) 0.371 (0.075)30 42.9 (37) 0.608 (0.361) 1468 (735) 0.804 (0.456) 8.4 (8.0) 0.141 (0.252)


of 9%. Thereafter, the tensile modulus remains almost constant while the tensilestrength decreases slowly. Maleic anhydride modi� ed polypropylene (MAPP)formed during the course of the reaction (Scheme 5) modi� es the reaction course.The bene� cial effects of maleated polypropylene on the strength properties ofcellulose � ber–polypropylene composites have been attributed to the esteri� cationreaction between cellulose � ber hydroxyl groups and the anhydride functionality ofmaleated PP [47]. A hypothetical model of the interface between MAPP with thecellulose OH of the sisal � ber is shown in Fig. 14. The strong interfacial adhesionbetween the treated � ber and PP matrix can be evidenced from the model (due tothe formation of MAPP graft).

Table 5 shows the effect of 9% maleic anhydride on tensile properties of sisal –PPcomposite at different � ber loading. It is clear that there is an increase in tensileproperties from 10% to 20% � ber concentration. On further increase of � berconcentration a leveling off is observed in tensile modulus while the tensile strengthshows a slight decrease. It was reported [48] that severe chain scission occurs inPP phase during the peroxide-catalyzed grafting PP. A higher amount of DCP wasthought to induce more chain scission and thus result in a decline in the stiffness.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 15. The effect of MAPP concentration of the tensile properties of sisal/PP composite at 20%� ber loading.

However, too large or too small a proportion of DCP is less advantageous to thebondability of the grafted PP.

3.5. Effect of maleic anhydride modi� ed polypropylene (MAPP) treatment

Figure 15 shows the effect of varying the concentration of MAPP (coupling agent)on tensile strength of sisal –PP composite at 20% � ber loading. With increase inMAPP concentration, the tensile strength is found to increase up to 10 wt% of theMAPP and then leveling off is observed. In the MAPP, maleic anhydride groups aregrafted on to the PP chain backbone as shown in Scheme 5. The increase in tensilestrength is due to the esteri� cation reaction between sisal � ber hydroxyl groupsand anhydride part of MAPP which causes a reduction in interfacial tension and anincrease in interfacial adhesion between PP and the � ber.

Table 6 shows the effect of 10% MAPP on tensile properties of sisal –PPcomposite at different � ber loading for both untreated and sodium hydroxidewashed � bers. The tensile strength increases up to 20% � ber content in the caseof untreated and NaOH washed � bers. A further increase in tensile strength isobserved in the case of washed � bers whereas a slight decrease is observed foruntreated � bers.

The excess maleic anhydride remaining after the formation of PP-graft-MA isdispersed in the matrix and modi� es the mechanical properties. The eliminationof pectic substances by washing of the � bers (with NaOH) is favorable for the

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Table 6.Effect of MAPP (10%) treatment on the tensile strength and modulus at different � ber loading

Fiber Tensile strength (MPa) Tensile modulus (MPa)

loading Case I Case II Case I Case II

Mean SD Mean SD Mean SD Mean SD

10 39.2 0.436 41.6 0.265 1086 0.872 1230 120 45.8 0.453 49.8 0.458 1466 0.436 1685 1.05230 44.78 0.544 53.4 0.361 1471 0.424 1735 0.566

SD — standard deviation; Case I — no NaOH pretreatment given to � ber; Case II — NaOHpretreated � ber.

Figure 16. SEM photograph showing the fractured surface of MAPP modi� ed sisal–PP composite(£200) (20% � ber loading).

mechanical properties of the composite. The longer, more � exible PP chain ofMAPP is able to diffuse more deeply into the matrix, become involved more fullyin interchain entanglements and thereby contributed to the mechanical contiguityof the system [48]. The chemical bonding between the anhydride and the hydroxylgroups of the � ber caused a better stress transfer from the matrix into the � bers,leading to a higher tensile strength [48]. The increased properties due to the MA-PPcoupling agent are mainly based on a reduction of � ber pull-out and less � ber onmatrix debonding [49, 50]. This should lead to micropores at the interphase [49].SEM investigations (Fig. 16) demonstrated that � ber pullout is reduced after themodi� cation with the coupling agent (MAPP). The improved � ber/matrix adhesionis due to the formation of bonds existing between � ber and matrix provided by thecoupling agent, and the stress transfer from matrix to � ber is improved leading toimproved reinforcing effect.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Table 7.Variation in tensile properties of benzoylated sisal � ber-PP composites with � ber content (� ber length6 mm)


10 37.8 (35.6) 0.3 (0.351) 768 (578) 0.608 (0.8) 8.4 (9.1) 0.36 (0.115)20 43.9 (36.5) 0.4 (0.252) 1268 (680) 0.424 (0.586) 7.6 (8.3) 0.32 (0.075)30 45.8 (37) 0.603 (0.361) 1342 (735) 0.458 (0.436) 7 (8.0) 0.2 (0.252)


Figure 17. SEM photograph of the fractured surface of benzoylated � ber composite (£800) (� bercontent 20 wt%).

The decrease in tensile properties of maleic anhydride treated composites overMAPP treated composites may be due to degradation of the PP matrix duringtreatment with DCP in the initial stage.

3.6. Effect of benzoyl chloride (benzoylation)

Table 7 shows the variation in tensile properties of benzoylated sisal –PP compositeswith � ber loading (� ber length 6 mm). Benzoylated � ber composite showsconsiderable improvement in tensile strength at all � ber loadings. The improvementin tensile strength is due to the better adhesion between the benzoylated � ber and thePP matrix, which can be evidenced from the SEM photomicrographs of the fracturedsurface of benzoylated � ber composite (Fig. 17). The fracture surface of treated� ber composite shows � ber breakage rather than pullout, which in turn indicatesbetter interfacial strength. As a result of benzoylation, the hydrophilicity of the � beris reduced, which makes the � ber more compatible with hydrophobic PP, thereby

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


increasing the properties of the resulting composite. Because benzoylation reducesthe modulus of the sisal � ber considerably [8], the modulus of the benzoylated � bercomposites was expected to be lower than that of untreated � ber composites. Thisis in fact true in the case of 10% treated sisal –PP composites. At 20 and 30%loading, however, the treated � ber composite shows improvement in modulus. The� ber /matrix adhesion in these cases is quite strong and overshadows the effect ofdecrease in modulus of the � ber upon benzoylation.

The hydrophilicity of the � ber is reduced due to the reaction between thecellulosic-OH group of the � ber and benzoyl chloride which may be shown as

Because some of the components of the � ber are extractable with NaOH, it isdif� cult to � nd the extent of reaction. A higher ratio of 1.5 g of benzoyl chloride for1 g of � ber can be used without signi� cant deterioration in the physical propertiesand � brous nature of the � ber and is the one used in the present work.

Upon benzoylation, � ber diameter decreases and hence the aspect ratio increases.This may be due to the leaching out of alkali-soluble fractions like waxy layer,lignin, etc. during alkali treatment and benzoylation. The reduction in the thicknessof the � ber upon benzoylation can be evidenced from the SEM photomicrograph asshown in Fig. 18. Moreover, the treatment provides a number of small voids on thesurface of the � ber that promote mechanical interlocking between the � ber and the

Figure 18. SEM photograph showing the surface of benzoylated sisal � ber (£400) (� ber content20 wt%).

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 19. A hypotheticalmodel of benzoylated � ber/PP interface.

matrix. SEM photographs also show a rough surface for the treated � ber. Therefore,the development of a rough surface topography and increase in aspect ratio givebetter � ber/matrix interfacial adhesion and an increase in mechanical properties. Ahypothetical model of benzoylated � ber-PP interface is shown in Fig. 19.

The IR spectrum of benzoylated � ber exhibited a number of characteristic bands.Hydroxyl vibration absorption at about 3400 cm¡1 diminished after benzoylationas a result of esteri� cation of the hydroxyl group. Absorption bands around 1950,1600 and 710 cm¡1 indicate the presence of aromatic groups, and the peaks around1725 and 1300 cm¡1 indicate the presence of ester groups.

3.7. Effect of permanganate treatment

Figure 20 shows the effect of permanganate concentration on the tensile propertiesof sisal –PP composites at 20% � ber loading. It is clear from the � gure thatpermanganate treatment of sisal � ber improves the tensile properties of PP–sisalcomposite, but improvement is only up to 0.05% concentration of permanganate.Beyond 0.05% concentration, the properties show a sharp decrease. This may bedue to the degradation of cellulose � bers at higher permanganate concentration.So the permanganate concentration is a critical factor in determining the tensileproperties of permanganate treated sisal – PP composites. The SEM photograph(Fig. 21) of the tensile fracture surfaces of the permanganate treated compositesindicate the grafting of PP on to cellulose � bers. It is also observable from Fig. 21that the broken end of the treated � ber is split due to strong interaction betweensisal � ber and PP matrix. The improved interaction can be explained in terms of thepermanganate induced grafting of PP on to sisal � bers as follows.

Cellulose H C Mn.III/ ! Cellulose H Mn.III/ .Complex/

Cellulose H Mn.III/ .Complex/ ! Cellulose· C HC C Mn.II/

Cellulose· C PP ! Cellulose PP·

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 20. The effect of permanganateconcentrationon the tensile properties of sisal–PP compositesat 20% � ber loading (£400).

Figure 21. SEM photographs showing (a) the surface of permanganate treated � ber, and (b) tensilefracture surface of the permanganate treated composites (� ber content 20 wt%).

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Table 8.Effect of KMnO4 (0.05%) treatment on the tensile properties of sisal–PP composites at different � berloading (� ber length 6 mm)


10 37.3 (35.6) 0.3 (0.351) 1109 (578) 0.451 (0.8) 8.6 (9.1) 0.058 (0.115)20 42.5 (36.5) 0.458 (0.252) 1195 (680) 0.36 (0.586) 8 (8.3) 0.1 (0.075)30 45.7 (37) 0.793 (0.361) 1271 (735) 0.424 (0.436) 7.6 (8.0) 0.08 (0.252)

Values given in parenthesis are those of untreated composites.

Cellulose PP· C nPP ! Cellulose PP·nC1

Cellulose PP·nC1 C Mn.III/ ! Cellulose PPnC1 C Mn.II/ C HC

The highly reactive Mn3C ion is responsible for initiating the graft reaction.Table 8 shows the tensile properties of permanganate treated (0.05%) sisal –PP

composites at different � ber loading. It is interesting to note that the tensileproperties of permanganate treated composite showed a signi� cant improvementas compared to untreated composites.

3.8. Comparative effectiveness of different treatments

After studying the tensile modulus and tensile strength of various treatments [alkali,PPG TDI (1 : 5 molar ratio), PMPPIC (10%), MAPP (6%), KMnO4 (0.05%),benzoylation], it is important to compare their relative effectiveness. It is interestingto note that all treatments improve the tensile properties of the composites todifferent extents.

Figures 22 and 23 represent the comparison in the tensile strength and tensilemodulus of the above mentioned treatments respectively at different � ber loading.It is interesting to note that all treatments improve the tensile properties of thecomposites to different extents. From the � gure it is clear that MAPP and isocyanatetreatments show superior tensile strength and modulus over other chemically treatedsisal � ber composites. The ef� ciency of the different treatments varies in the order:NaOH < KMnO4 < benzoylation < PMPPIC < PPG-TDI < MAPP.

From an economic point of view, alkali treatment is very cheap. MAPP treatmentand KMnO4 are also not very expensive since the amount of the reagents requiredis very small. Figure 24 shows the stress– strain behavior of composites at differentchemical treatments. It is found that treated composites show superior stiffnesscompared to untreated � ber composites.

3.9. Theoretical modeling

Modulus is a bulk property which depends primarily on geometry, particle sizedistribution and concentration of the � ller. But tensile strength of a composite

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 22. The comparison of the tensile strength of different chemically treated � ber composites atdifferent � ber loading (� ber length 6 mm).

depends strongly on the local polymer/ � ller interaction as well as the above factors.The � ller particle geometry has a signi� cant in� uence on the strength of a � lledpolymer. In literature, a number of theories and equations have been developedto predict the tensile properties of the composites. These are (1) Modi� ed ruleof mixtures (MROM); (2) Series model, (3) Parallel model, (4) Hirsch model,(5) Halpin–Tsai model and (6) Bowyer–Bader’s model.

3.9.1. Modi�ed rule of mixtures (MROM). The modi� ed rule of mixtures [51]can be given as follows.

Tc D Tm.1 ¡ Vf/ C TfVfe; (3)

where Tc is the ultimate strength of composites, Tm is the matrix strength atthe failure strain of the � ber, Tf is the ultimate strength of � ber, Vf is the � bervolume fraction and Vfe is the effective � ber volume fraction. The effective � bervolume fraction is given in terms of the � ber volume fraction and the ratio of realcontribution as follows.

Vfe D Vf.1 ¡ P /; (4)

where P is the degradation parameter for the effective � ber volume fraction,lying between 0 and 1. P can be calculated from the microgeometry of thecomposite components and depends only on the � ber volume fraction because the

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 23. The comparison of the tensile modulus of different chemically treated � ber composites atdifferent � ber loading (� ber length 6 mm).

Figure 24. Effect of different chemical treatments on stress–strain behavior of sisal–PP composites.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


microgeometry is intimately related to the � ber volume fraction under identicalmanufacturing conditions.

P can be calculated from the equation,

P D1Tc

TfVf; (5)

where 1Tc is the difference between the experimentally measured strength and thestrength predicted by the rule of mixtures.

3.9.2. Parallel and series models. The parallel and series models [52] are used todetermine the modulus and tensile strength of short � ber composites. The equationsfor tensile strength are

Tc D TfVf C TmVm (Parallel model); (6)

Tc DTmTf

TmVf C TfVm(Series model); (7)

where Tc, Tm and Tf are the tensile strength of the composite, matrix and � berrespectively. If modulus is the parameter under study, notations such as Mc, Mm andMf may be used instead of Tc, Tm, and Tf where Mc, Mm and Mf are the Young’smoduli of composite, matrix and � ber respectively.

3.9.3. Hirsch model. The Hirsch model [53] is a combination of parallel andseries models. Using this model, the tensile strength and Young’s modulus aredetermined by the equations,

Tc D x.TmVm C TfVf/ C .1 ¡ x/TfTm

.TmVf C TfVm/; (8)

where x is a parameter which determines the stress transfer between the � ber andmatrix.

In terms of modulus, the equation is

Mc D x.MmVm C MfVf/ C .1 ¡ x/MfMm

MmVf C MfVm: (9)

3.9.4. Halpin–Tsai model. Several researchers used this model [54] to deter-mine the properties of composites that contain discontinuous � bers oriented in theloading direction. The tensile strength can be calculated using the model as follows.

Tc D Tm

³1 C A´Vf

1 ¡ ´ÃVf

´; (10)

where

´ DTf=Tm ¡ 1Tf=Tm C A

; (11)

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


where A is the measure of � ber geometry, � ber distribution and � ber loadingconditions,

Ã D 1 C³

1 ¡ Ámax

Á2max

´Vf; (12)

where Ámax is the maximum packing fraction which has a value 0.785 for squarearrangement of � bers and 0.907 for hexagonal array of � bers and 0.82 for randompacking of � bers.

A D K ¡ 1; (13)

K D 1 C 2l=d; (14)

where l and d are the length and diameter of the � ber used.

3.9.5. Bowyer–Bader’s model. According to Bowyer–Bader’s [55] model, thetensile strength is given by

Tc D TfK1K2Vf C TmVm; (15)

where K1 is the � ber orientation factor. Depending on � ber orientations, K1 alsochanges. K2 is the � ber length factor.

For � bers with

` > `c; K2 D ` ¡ `c=2`: (16)

For � bers with

` < `c; K2 D `=2`c; (17)

where ` is length of � ber and `c its optimum length. According to the above model,Young’s modulus also can be calculated using the equation.

Mc D MfK1K2Vf C MmVm: (18)

The experimental and theoretical values of tensile strength of the composite(MAPP treatment) as a function of � ber loading are given in Fig. 25. Onanalyzing the � gure, it is very clear that the experimental value exactly � ts withthe theoretical value in the case of the modi� ed rule of mixtures. It is assumedthat the model predicts the actual composite strength because the value of ½

(as suggested by MROM) is de� ned to account for the microgeometry of realcomposites [51]. Halpin–Tsai and Series models show negative deviation fromexperimental value. The Hirsch model is in close agreement with the experimentalvalue but the Bowyer–Bader model and Parallel model show positive deviationfrom experimental value at all � ber loadings, which increases with � ber loading.

The Young’s modulus value of the composite samples (MAPP treatments) arecompared with the theoretical predictions in Fig. 26. It is interesting to note that at

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


Figure 25. The experimental and theoretical value of tensile strength of MAPP treated composite asa function of � ber loading (� ber length 6 mm).

Figure 26. The experimental and theoretical values of tensile modulus of MAPP treated compositeas a function of � ber loading (� ber length 6 mm).

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


all � ber loadings, the Parallel model shows positive deviation while other models— Series, Hirsch (value of x D 0:1), Halpin–Tsai, and Bowyer–Bader’s models —show negative deviation to different extents. But at 10% � ber loading, in the case ofthe Parallel model, the extent of deviation is much less and it is in good agreementwith the experimental value.

The deviation from the experimental data is because of various reasons, suchas presence of voids and � ber agglomeration at higher � ber loading. Moreover,most of the models assume a cylindrical shape for the � bers while sisal � ber is notperfectly cylindrical due to surface irregularities which is evident from Fig. 1a. Thechance of formation of transcrystallinity at the � ber–matrix interface also affectsthe tensile properties of composites which is not accounted for in any of the abovemodels. Since the models used in the study do not take account of the presenceof voids, � ber–� ber interactions, non-uniform shape of sisal � ber and formationof transcrystallinity at the interphase between the � ber and the matrix, the modelsshow some deviations from the experimental behavior.

4. CONCLUSION

The in� uence of various chemical treatments like alkali, isocyanates, maleatedpolypropylene grafts, benzoylation and permanganate on the tensile properties ofsisal –PP composites was studied. Mechanical anchoring of PP-matrix onto � bersis proposed to be responsible for the observed improvement in adhesion during thealkali treatment. In addition to this, other factors like rough surface topography,which increased aspect ratio during alkali treatment, also favors better tensileproperties. The superior mechanical properties exhibited by the urethane derivativeof sisal –PP composites may be due to the fact that the long chain structureof the urethane part linked to the cellulosic � bers makes the � ber hydrophobic,compatible and highly dispersible in the PP matrix. SEM photographs also suggestthe strong � ber–matrix adhesion in sisal –PP composites. The grafting of sisal� bers by PP-graft-MA occurs more readily on cellulose for washed � bers (alkaliwashed) and leads to composites with higher tensile strength than for untreated� bers. SEM investigations demonstrated that � ber pullout is reduced after themodi� cation with the PP-g-MA. The improved � ber–matrix adhesion is due tothe bond formed between � ber and matrix provided by the coupling agent (PP-g-MA), and the stress transfer from matrix to � ber is improved leading to highreinforcing effect. Benzoylation of the sisal � ber considerably improves the tensileproperties of the composite. Permanganate-treated composite also showed a similartrend because of the permanganate-induced grafting. Among the various typesof chemical treatments, maleated polypropylene grafts and isocyanate treatmentsshowed the most useful properties. Finally, the experimental results were comparedwith theoretical predictions.

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


REFERENCES

1. J. O. Karlsson, J. F. Blachot, A. Peguy and P. Gatenholm, Polym. Compos. 17, 300 (1996).2. C. Klason, J. Kubat and P. Gatenholm, in: ACS Symposium Series, Viscosity of Biomaterials,

W. Glasser (Ed.) (1990).3. P. Zadorecki and A. J. Mitchell, Polym. Compos. 10, 2 (1989).4. R. G. Raj, B. V. Kokta, D. Maldas and C. Daneault, J. Appl. Polym. Sci. 37, 1089 (1989).5. K. Joseph, S. Thomas, C. Pavithran and M. Brahmakumar, J. Appl. Polym. Sci. 47, 1731 (1993).6. J. George, S. S. Bhagawan, N. Prabhakaran and S. Thomas, J. Appl. Polym. Sci. 57, 843 (1995).7. P. V. Joseph, K. Joseph and S. Thomas, Compos. Sci. Technol. 59, 1625 (1999).8. K. C. Manikandan Nair, S. M. Diwan and S. Thomas, J. Appl. Polym. Sci. 60, 1483 (1996).9. J. M. Felix and P. Gatenholm, J. Appl. Polym. Sci. 42, 609 (1991).

10. I. Ulkem and H. P. Schreiber, Composite Interfaces 2, 253 (1994).11. A. Gati and H. D. Wagner, J. Adhesion 58, 25 (1996).12. J. Gassan and A. K. Bledzki, Angew. Makromol. Chem. 236, 129 (1996).13. D. Maldas, B. V. Kokta, R. G. Raj and C. Daneault, Polymer 29, 1255 (1988).14. D. Maldas and B. V. Kokta, J. Appl. Polym. Sci. 40, 917 (1990).15. P. Bataille, L. Ricard and S. Sapieha, Polym. Compos. 10, 103 (1989).16. D. Maldas and B. V. Kokta, J. Appl. Polym. Sci. 41, 185 (1990).17. R. G. Raj, B. V. Kokta, D. Maldas and C. Daneault, Polym. Compos. 9, 404 (1988).18. C. Joly, R. Gauthier and B. Chabert, Compos. Sci. Technol. 56, 761 (1996).19. A. K. Bledzki, S. Reihmana and J. Gassan, J. Appl. Polym. Sci. 59, 1329 (1996).20. S. H. Zeronian, H. Kawabata and K. W. Alger, Text Res. Inst. 60 (3), 179 (1990).21. M. A. Semsazadeh, Polym. Compos. 7 (1), 23 (1986).22. E. T. N. Bisanda and M. P. Ansell, Compos. Sci. Technol. 41, 165 (1991).23. P. K. Ray, A. C. Chakravarty and S. B. Bandyopadhyay, J. Appl. Polym. Sci. 20, 1765 (1976).24. S. C. O. Ugbolue, Text. Inst. 20 (4), 1 (1990).25. A. N. Shan and S. C. Lakkard, Fiber Sci. Technol. 15, 41 (1985).26. L. Hua, P. Flodin and T. Ronnhult, Polym. Compos. 8 (3), 203 (1987).27. A. D. Beshay, B. V. Kokta and C. Daneault, Polym. Compos. 6, 261 (1985).28. R. G. Raj, B. V. Kokta and C. Daneault, J. Adhesion Sci. Technol. 3, 55 (1989).29. R. G. Raj, B. V. Kokta, G. Groleau and C. Daneault, Plast. Rubber Proc. Appl. 11, 215 (1989).30. B. V. Kokta, D. Maldas, C. Daneault and P. Beland, Polym. Plast. Technol. Engng. 29, 87 (1990).31. S. Sapieha, P. Allard and Y. H. Zang, J. Appl. Polym. Sci. 41, 2039 (1990).32. S. Sapieha, J. F. Pupo and H. P. Schreiber, J. Appl. Polym. Sci. 37, 233 (1989).33. P. Cousin, P. Bataille, H. P. Schreiber and S. Sapieha, J. Appl. Polym. Sci. 37, 3057 (1989).34. P. Flink, M. Rigdahl and B. Stenberg, J. Appl. Polym. Sci. 35, 2155 (1988).35. K. Joseph, S. Thomas and C. Pavithran, Polymer 37, 5139 (1996).36. S. S. Tripathy, S. Jena, S. B. Misra, N. P. Padhi and B. C. Singh, J. Appl. Polym. Sci. 30, 1399

(1985).37. S. Moharana, S. B. Misra and S. S. Tripathy, J. Appl. Polym. Sci. 40, 345 (1990).38. G. Samay, T. Nagy and J. L. White, J. Appl. Polym. Sci. 56, 1423 (1995).39. F. Hyndryckx, P. H., Dubois, M. Patin, R. Jerome, P. H. Teyssie and M. Garcia Marti, J. Appl.

Polym. Sci. 56, 1093 (1995).40. P. Hedenberg and P. Gatenholm, J. Appl. Polym. Sci. 56, 641 (1995).41. A. R. Sanadi, C. Clemons, R. M. Rowell and R. A. Young, J. Reinforced Plast. Compos. 13, 54

(1994).42. S. George, R. Joseph, S. Thomas and K. T. Varughese, Polymer 36, 54 (1994).43. C. Saha, B. K. Das, P. K. Ray, S. N. Pandey and K. Goswami, J. Appl. Polym. Sci. 43, 1885

(1991).44. S. Varghese, B. Kuriakose, S. Thomas and A. T. Koshy, Indian J. Nat. Rubber Res. 4, 55 (1991).

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3


45. H. W. Siesler and K. H. Meritz, Infrared and Raman Spectroscopy of Polymers. Marcel Dekker,New York (1980).

46. B. S. Westerlind and J. C. Berg, J. Appl. Polym. Sci. 36, 523.47. M. Kazayawoko, J. J. Balatinecz and R. T. Woodhams, J. Appl. Polym. Sci. 66, 1163– 1173

(1997).48. N. G. Gaylord and M. K. Mishra, J. Polym. Phys. Polym. Lett. Ed. 21, 23 (1983).49. A. Karmaker and J. Schneider, J. Mater. Sci. Lett. 15, 201 (1996).50. S. Dong, S. Sapieha and H. P. Schreiber, Polym. Eng. Sci. 33, 343 (1993).51. C. Lee and W. H. Wang, J. Mater. Sci. 17, 1601 (1998).52. L. J. Broutman and R. M. Krock, Modern Composite Materials. Addison Wesley, Reading, MA

(1967).53. T. J. Hirsch, J. Am. Composition Inst. 59, 427 (1962).54. L. E. Nielsen, Mechanical Properties of Polymers and Composites, Vol. 2. Marcel Dekker, New

York (1974).55. W. H. Bowyer and M. G. Bader, J. Mater. Sci. 7, 1315 (1972).

Dow

nloa

ded

by [

Aca

dia

Uni

vers

ity]

at 0

5:53

02

May

201

3

Short sisal fiber reinforced polypropylene composites: the role of interface modification on...

Documents

Transcript of Short sisal fiber reinforced polypropylene composites: the role of interface modification on...