Fibre-matrix adhesion and properties evaluation of sisal polymer ...

Fibers and Polymers 2015, Vol.16, No.1, 146-152 DOI 10.1007/s12221-015-0146-2

ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version)

Fibre-matrix Adhesion and Properties Evaluation of Sisal Polymer Composite Ruhi Haque*, Mohini Saxena, S. C. Shit1, and P. Asokan CSIR-Advanced Materials and Processes Research Institute, Bhopal 462064, India Central Institute of Plastics Engineering and Technology, Ahmedabad 382445, India (Received November 26, 2013; Revised June 25, 2014; Accepted August 2, 2014)

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Abstract: Fibre matrix adhesions of sisal fibre with polymer were evaluated in terms of physico-chemical and mechanical properties. Effects of acetylation, acrylation, silanization, alkalization, and permanganate treatment on physical and chemical parameters as well as mechanical parameters such as tensile and impact behavior were investigated. Physical properties like density, moisture absorption, water absorption, void content and chemical properties like percentage of lignin, cellulose, and hemicelluloses were determined. From the findings, it was concluded that treatments such as acetylation, acrylation, and silanization can increase interfacial strength, wetting, and compatibility between fibre and matrix, leading to increase composite tensile strength. Acetylated sisal fibre and its polymer composites showed the highest tensile strength, less water absorption, and the acrylated sisal fibre composites showed the highest impact strength (46900 J/m2). Keywords: Fibres, Interfacial strength, Mechanical properties

micrograph of cross section of sisal fibre (bundle of fibrils) is shown in Figure 1 which shows that each individual fibre cell is made up of four main parts, namely the primary cell wall, the thick secondary wall, the tertiary wall and the lumen. The tensile properties of sisal fiber are not uniform along its length, i.e. stronger and stiffer at midspan and have moderate properties at tip. Almost 70 % of the fibres have a tensile strength in the range 200 to 400 MPa, tensile modulus in the range of 9-40 GPa and elongation at break (%) in the range 2-14 [1-6]. Mechanical properties of sisal with other natural fibres are summarized in Table 1. But due to the low interfacial adhesion between fibre and polymer matrix in composite, attracts researchers to optimize the interface of fibres [7]. Several mechanisms of activation of fibre i.e. highly cross linked structure formation, elimination of weak boundary layers, formation of tough or flexible layer, improvement in wetting between polymer and fibre etc were outlined. Rong et al. [8] optimized that alkalinized, acetylated, cyanoethylated; silanized sisal shows significantly improve adhesion as filler in epoxy composite. Ferreira et al. [9] characterized benzoylated sisal fibre and found many morphological changes such as the losses of the parenchyma cells, the defibrillation of the technical fibres into ultimate fibres, the micro fibrillation of the ultimate fibres, benzyl incorporation, overall mass gain etc. Valadez-Gonzalez et al. [10] concluded that the alkali treatment increases number of possible reaction site by increasing surface roughness. In respect to thermal behavior, Joseph et al. [11-13]. observed that urethane derivative of polypropylene glycol, maleic anhydride modified polypropylene and KMnO4 modified sisal exhibited an increased crystallization temperature and crystallinity Bismarck et al. [14] obtained increase performance of grafted sisal which confirms that more accessibility of surface functional groups resulted in lower zeta potential. Li et al. [15] found that permanganate and DCP-treated sisal fibre

Introduction The performance and properties of composite materials depend on the characteristics of the individual components and their interfacial compatibility. The use of polymers with fillers like short natural fibre reinforcement has grown rapidly due to their good processability, ability to recycle, non abrasive nature, less environmental pollution, combustibility, light weight, high stiffness, high strength, biodegradability and improved physico-mechanical properties. Among different natural fibres, utilization of sisal as reinforcing agent is increase day to day. Sisal fibre is a cellulose reinforced lignin composite material with high tensile strength and modulus, makes it suitable for reinforcement in composites for various applications [1-3]. The electron

Figure 1. Cross section of sisal fibre.

*Corresponding author: [email protected] 146

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Table 1. Physico-chemical and mechanical properties of different fibre Tensile Hemi Moisture Microfibriller Density Cellulose Wax Lignin Ash strength cellulose content angle 3 (g/cm ) (%) (%) (%) (%) (MPa) (%) (%) (o) Sisal 1.4 67-78 10.0-14.2 8.0-11.0 11.0 20.0 468-640 Coir 36-43 0.15-0.25 41-45 8.0 41-45 131-175 Oil palm 65 19 2 46 248 Jute 1.3-1.46 61-71 13.6-20.4 12- 13 12.6 8.0 0.5 393-800 Cotton 1.4 83 6 1 3 0.6 287-597 Flax 1.4-1.5 71-78 18.6-20.6 2.2 10.0 1.5 10.0 1.7 345-1500 Hemp 1.48 70.2-74.2 17.9-22.4 3.7-5.7 10.8 2.6 6.2 0.8 270-900 Banana 1.350 63-64 19 5 10-11 11 559±6.7 PALF 1.526 81 12.7 13.5 14 413+8 Glass 2.56 Nil Nil Nil Nil Nil 2000-3400 Carbon 2.54 Nil Nil Nil Nil Nil 2000 - 3500 Fiber

have lower tensile strength and fibre-matrix interphase adhesion as compared to silane coupling. Joseph et al. (2003) found CTDIC (Caranol derivative of toluene isocyanate) reduced hydrophilic nature thereby increasing the tensile properties and other treatment like sodium hydroxide, isocyanate, permanganate, peroxide also enhanced the mechanical properties at various extent of sisal polyethylene composite. Sydenstricker et al. [16] concluded that the 2 % N-iso propyl acrylamide shows best mechanical properties among different treated sisal reinforced polyester composite. Mishra et al. [18] observed that cyanoethylated treated sisal polyester composite had maximum tensile strength (84.29 MPa), alkali treated sisal polyester composite showed best flexural (153.9 MPa) and impact strength (197.88 J/m), which is 21.8 % and 20.9 % higher than untreated composite. Martins et al. [19] determined the best treatment condition for sisal fibres by mercerization (5 % NaOH, 3 h, 50 oC) and acetylation for 15 minutes with the help of NMR studies. Djdjelli et al. [20] assessed maleic anhydride treated sisal showed less moisture absorption, thus increasing mechanical performance. Stress transferability is mainly depends on the extent of interfacial interaction between the fibre and matrix. Extent of forming mechanical and chemical interlocking at the interface is influenced by surface morphology and chemical composition of fibres, reactive probes availability and polarity of the matrix resin and also by the hydrophilicity of the fibre [20]. Since the interface plays a major role in transferring the stress from the matrix to the fibre, it is important to work on fibre surface to increase interfacial adhesion between the fibre and matrix in composite.

Experimental Materials Sisal fibre was used as a reinforcing medium in making

Young’s Elongation modulus at break Reference (GPa) (%) 9.4-22 3-7 [27,28] 4.0-6.0 15-40 [28] 6.70 14 [28] 10-30 1.5-1.8 [07] 5.5-12.6 7.0-8.0 [29] 10-80 2.7-3.2 [30] 20-70 2.7-3.2 [07] 20 5-6 [30] 4.2 3-4 [30] 72 1.8-3.2 [31] 70 2.5 [32]

sisal reinforced polyester composite. The commercial grade unsaturated polyester resin (Polylite PO-9123) was used as a binder. Glacial acetic acid, ethyl acetate, concentrated sulfuric acid, KMnO4, acetone, NaOH, water, three amino-propyl trimethoxy Silane, acryl amide were obtained from Merk and used as received. Method Chemical Treatment In acetylation, chopped sisal fibre was kept soaked in glacial acetic acid for 1 hour at room temperature and after acid decantation, the fibres were soaked for 10 min in ethyl acetate containing two drops of concentrated sulphuric acid, dried in an oven at 40 oC for 24 hours after separation and washing. In acrylation, fibres were treated with 2 % acrylamide solution (aqueous) for the duration of two hours and dried after separation. In alkali treatment, sisal fibres were treated with 5 % NaOH solution, washed with distilled water and dried in air oven for 24 hours at 40 oC. In permanganate treatment, alkali treated sisal fibre were dipped in 0.5 % KMnO4 solution for one minutes duration and dried in an air oven at 40 oC after separation and washing. In silane treatment, sisal fibre were treated with 1 % silane A 174 (three amino-propyl trimethoxy silane) solution in acetone for 3 hours and air dried after in an oven at 40 oC. Fabrication Composite fabricated by hand layup technique in the ratio of 2:1 of polymer and sisal fibre with 2 % accelerator and 2 % hardener. Characterizations Physical Properties Density of composite had calculated according to ASTM D792. Water uptake studies were carried out according to ASTM D570-98. Moisture absorption capacity of sisal and sisal composite has been determined on LCGC moisture absorption analyzer, at AMPRI, Bhopal.

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Chemical Properties Determination of lignin content by gravimetric method: 1.5 g fibres (Ws) were treated with 72 % H2SO4 solution and then submitted to reflux for 4 hours after adding 560 ml distilled water. Filter and oven dried at 105 oC for 2 hours and weigh (W2). Again kept the crucible in the furnace at 550 oC for 3 hrs and weigh it (W1). % Lignin = W2 − W1/Ws × 100 Determination of cellulose: 1 g sisal (Ws) was treated with 25 ml of 80 % acetic acid, 1 ml of conc. HNO3 and refluxed. After filtration, centrifuge and finally oven dried the precipitate at 105 oC for 1 hrs and weighed (W2). Again kept the crucible in the furnace at 550 oC for 3 hrs and weigh it (W1). The percentage of cellulose calculated as % Cellulose = W2 − W1/Ws × 100 Determination of hemicelluloses: 0.5 g sisal was treated with 5 % KOH solution. Then hemicelluloses are quantitatively precipitated by the addition of alcohol (ethanol) and separate out in a crucible after centrifugation. Then dried at 105 oC in oven for 2 hrs and weighed it (W2). Again kept the crucible in the furnace at 550 oC for 3 hrs and weigh it (W1). Hence the hemicelluloses percent compositions of the samples were calculated as follows: % Hemicelluloses = W2 − W1/Ws × 100 [21] where, W1=dried weight of hemicelluloses precipitate W2=dried weight of hemicelluloses sample Measurement of Void Content Void contents of the sisal polyester composites was measured using V = 100 (ρth – ρm)/ρth

where ρth is the theoretical composite density, ρm is the measured composite density. Theoretical density (ρth) was calculated according to the following equation ρth = Vf · ρf + (1 − Vf) ρr where Vf is the sisal fibre in volume %, ρr is the density of the resin and ρf is the density of sisal fibre. The void structure of composite was also examined with a JEOL SCAN Electron Microscope at AMPRI [18]. Mechanical Properties Tensile strength of sisal fibre and their composite were evaluated on AMETEK LLOYD instruments according to ASTM D638. Impact strength of composite was evaluated on Impact tester make Tinius Olesen, according to ASTM D256. SEM Studies of Fractured Sisal Composite Fibre-matrix interphase evaluated through surface studies by SEM (JEOL).

Results and Discussion Physico-chemical Properties of Sisal Fibre and Its Polyester Composite Physical parameter like density, moisture absorption, water absorption, void content and chemical parameter like percentage of lignin, cellulose, and hemicelluloses were determined and summarized in Table 2. Density of treated fibres was found to be decreasing due to the removal of lignin, hemicelluloses, wax and other impurities. In case of composite, density of sisal reinforced polyester composite was higher than the density of neat polyester composite. Little quantity of water or moisture can considerably vary

Table 2. Physical and chemical parameter of sisal fibre and sisal-polyester composite S. no. 1 2 3 4 5 6 7 8 9 10 11 12 13

Sample name USF - Untreated sisal fibre AceTSF - Acetylated treated sisal fibre AcrTSF - Acrylamide treated sisal fibre AlTSF - Alkali treated sisal fibre PTSF - Permanganate treated sisal fibre SiTSF - Silane treated sisal fibre USPC - Untreated sisal polyester composite AceTSPC - Acetylated treated sisal polyester composite AcrTSPC - Acrylamide treated sisal polyester composite AlTSPC - Alkali treated sisal polyester composite PTSPC - Permanganate treated sisal polyester composite SiTSPC - Silane treated sisal polyester composite Polyester resin

Moisture Water Hemi Cellulose Density absorption absorption celluloses 3 (%) (g/cm ) (%) (%) (%) 1.45 16.46 45 14.2 0.913 3.60 38.5 12.5 0.907 1.37 45 11.2 0.861 2.13 40 10.8 0.873 4.32 42.5 13.5 0.890 3.89 40 13.8 1.24 2.96 26 1.22 1.79 6.7 1.24 1.98 10 1.218 2.37 15 1.25 2.28 25 1.25 0.88 7.8 1.16 0.36 5.0 -

Lignin (%) 20.5 4.5 4 3.5 18.5 12.5 -

Void content (vol %) 4.38 2.8 2.8 4.38 2.04 2.04 -



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Figure 2. Void structure of untreated sisal polyester composite.

the mechanical properties of natural fibre reinforced composite [18]. Seventy five percent reductions in moisture absorption of treated sisal fibre were found in comparison to untreated sisal fibre. Among all treated fibre, acryl amide treated sisal showed least moisture absorption value (1.37 %) instead of 16.46 % of untreated fibre. Moisture absorption and water absorption study of composite showed a decrease from untreated sisal reinforced polyester composite to treated sisal polyester composite and among them silane and acetylated treated showed best results. The reason behind that is the hygroscopic nature of fibres cell wall is greatly reduced due to the swelling of cell wall after acetylation which increased dimensional stability of fibres [23] and in case of Silane treatments, surface coating to the fibres reduces the water absorption. Determination and comparison of chemical composition reveals that the % amount of lignin and hemicellulose decreases remarkably with respect to cellulose content after treatment. Void (Figure 2) is the property of composite, which is formed due to insufficient adhesion and, incompatibility between fibre and matrix in the composite and affects the physico-mechanical properties. It was found that void content of composite decreases 2 to 4.5 volume % after treatments (least in permanganate and silane treated composite). This shows that compatibility between fibre and polymer increases.

Mechanical Properties of Sisal Fibre and Its Polyester Composite Tensile Strength of Sisal Fibre Optimum tensile properties were observed for acetylated fibre and acrylated treated sisal fibre which is reported in Table 3. Acetylated and acrylated sisal showed higher tensile strength i.e. 897 MPa and 855 MPa respectively in comparison to untreated sisal 698 MPa. Sisal treated with silane, alkali and permanganate showed a decreasing trend in tensile strength with respect to acetylated and acrylated but all treatment showed higher tensile strength in comparison with

Figure 3. Tensile strength of different raw and treated sisal fibre.

Table 3. Tensile strength of untreated and treated sisal fibre Type of sisal fibre UNS - Untreated sisal AceTSF - Acetylated treated sisal fibre AcrTSF - Acrylamide treated sisal fibre AlTSF - Alkali treated sisal fibre PerTSF - Permanganate treated sisal fibre SiTSF - Silane treated sisal fibre

Diameter 0.12 mm 0.09 mm 0.09 mm 0.075 mm 0.071 mm 0.10 mm

Load at maximum load 805 gf 582 gf 555 gf 359 gf 316 gf 641 gf

Strain at maximum load 0.03597 0.02822 0.01965 0.02070 0.01769 0.02896

Tensile strength (MPa) 698.41 897.82 855.16 797.86 782.25 801.24

Stiffness (kN/m) 6.3493 5.4244 8.5063 5.3181 5.2584 6.8041

Young’s Percentage total modulus elongation at (MPa) fracture (%) 28070 3.6056 42633.0 2.8225 66855.0 1.9653 60188.0 2.0777 66408 2.0830 43316 2.8964

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Table 4. Mechanical properties of sisal-polyester composite (40 %fiber volume) S. no.

Chemically treated sisal polyester composite

Density (g/cm3)

1

USPC - Untreated sisal polyester composite

1.24

13.0

2.9

50.18

2

AceTSPC - Acetylated treated sisal polyester composite

1.22

13.0

2.8

64.37

3

AcrTSPC - Acrylamide treated sisal polyester composite

1.24

13.0

2.9

60.51

4

PTSPC - Permanganate treated sisal polyester composite

1.25

13.0

3.0

60.49

5

AlTSPC - Alkali treated sisal polyester composite

1.22

13.0

2.9

52.95

6

SiTSPC - Silane treated sisal polyester composite

1.25

13.0

4.2

51.86

7 NPC - Neat polyester composite

5.36

13.0

5.8

7.42

Width Thickness (mm) (mm)

untreated sisal. Elongation at break (%) was found to be higher in untreated sisal because of cementing agent present in sisal fibrils, which opposes the deformation, whereas acrylation and acetylation also showed considerable elongation. The young’s modulus of the fibre was improved due to crystalline region of the fibre (cellulose). The stress-strain curve of treated and untreated sisal fibre is given in Figure 3. Each individual fibre is bounded by non-cellulosic substance like lignin, pectin etc. Failure of the fibre occurs gradually upon the stress application. Increase of the stress causes the rupture of the cell walls and decohesion of cells. This property may be understood from the stress-strain curve slope. Stress-strain curve of the treated fibre showed that the cementing material is removed after treatment [5]. Mechanical Properties of Sisal Polyester Composite Tensile Properties Tensile properties of 40 % sisal fibre volume sisal-polyester composite were examined and summarized in Table 4 which revealed that the acetylated sisal-reinforced polyester composite showed highest tensile strength (64.37 MPa) in comparison with 5 % alkali treated sisal composite which showed least tensile strength (52 MPa). Tensile strength of acryl amide treated (61 MPa), permanganate treated (61 MPa) and silane treated sisal composite (51.86 MPa) also found greater than untreated sisal composite (50.18 MPa). Since acryl amide and acetylated treatment showed lesser moisture absorption and water absorption which is reflected in increased interfacial adhesion and compatibility, and finally in higher tensile properties. On the other side, Alkali increases the brittleness of fibre by removal of lignin, which might have resulted in lowering in mechanical properties. Acryl amide treatment gradually attacks the fibers inner layer, significantly alter its surface and react with cellulose

Tensile strength (MPa)

Tensile strength Impact strength Young Load at Elongation Temp. Strength modulus max load (%) (oC) (J/m2) (GPa) (kN) RT 24700 1.15 8.45 2.17 100 33000 RT 21600 1.41 6.40 2.34 100 19600 RT 46900 1.15 7.74 2.28 100 33300 RT 25000 1.24 6.51 2.35 100 17740 RT 14750 1.16 5.64 2.0 100 25000 RT 13950 1.079 6.09 2.830 100 12050 74.39 16.07 0.56 RT 2380

fibrils [20]. In case of permanganate treated sisal fibre, surface was etched and became quite rough due to the oxidation function of the permanganate which increases mechanical interlocking between fibre and polymer matrix [5,18,24]. On other side, silane coated cellulose has – OH groups which interacts with polymer more effectively and increases tensile properties [17,25]. Hence, Chemical bonding with mechanical interlocking affect the frictional shear stress transfers across the interface [24]. Impact Strength Ability of a material to resist the fracture under stress applied at high speed is known as impact strength which is directly related to overall toughness of material [26]. Impact strength of 40 % fibre volume treated sisalpolyester composite showed ten times increase in impact strength with respect to neat polyester composite (in Table 4). Fibres may impart a remarkable effect on the impact resistance through the principle of stress transfer. Among alkali, Silane, acryl amide, acetylated, permanganate and untreated sisal polyester composite, acryl amide composite showed highest improvement in impact strength at room temperature and at 100 oC both. The acryl amide treated sisal polyester composite showed highest impact strength i.e. 46900 J/m2 at room temperature which decreases on increasing the test temperature at 100 oC and becomes 33300 J/m2. Morphology of Sisal Fibre and Fractography of Sisal Fibre Reinforced Polyester Composite SEM micrographs of tensile fractured surfaces clearly reveal the interfacial adhesion between the fibre and matrix. Figure 1 shows the bundle structure of sisal fibre formed by elementary fibres held together mainly by lignin, pectin and amorphous polymer found in the primary cell wall and in the



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Figure 4. Scanning electron microscope of sisal polyester composite.

middle lamellae region. Fibrillation is observed between fibre-cells in treated sisal fibre (Figure 4(a)) and this fibrillation between fibrils resulted in the small non-linear region, in the stress-strain curve, prior to failure of the fibre as shown in the Figure 3. Initiation of fracture of the individual fibre-cells was also observed in Figure 4(b). More roughness of sisal surface observed in SEM of treated sisal in Figure 4(d) as compare to the surface of raw sisal in Figure 4(c). This increased roughness surfaces are responsible for increased mechanical interlocking [27]. SEM of cross section of tensile fractured surface of untreated sisal polyester composite as shown in Figure 4(f), containing the gap between the fibre and matrix shows less interfacial adhesion whereas SEM of long length sisal at tensile fracture surface

of treated sisal polyester composite shown in the Figure 4(e) occurs due to the increase interfacial adhesion and high mechanical properties.

Conclusion Fibrous reinforcement in Polyester resin enhanced the physico-chemical and mechanical properties of the composite. Treatments can deactivate the cellulosic hydrophilic groups, increases roughness and fibrillation of fibre and due to deactivation of hydrophilic moiety on lignocellulosic fibre, moisture absorption, water absorption decreased and mechanical properties in composites were increased. Increased surface roughness and surface area can also increase the mechanical

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interlocking leading to increase in the fibre-matrix bonding. Results revealed that various treatments (acetylation, acrylation, alkalization, permanganate treatment, silanization) of sisal fiber improved surface properties by altering morphology, chemical composition and hydrophobic character. Among all treatments, acetylation resulted in optimum tensile strength (897 MPa) and acetylated sisal fiber reinforced polyester composites showed increased tensile strength (64.37 MPa) in comparison to untreated sisal reinforced polyester composite (56.47 MPa) because acetylation deactivated the hydrophilic moiety on cellulosic fibre. Acryl amide treated sisal fiber reinforced polyester composite showed highest impact strength (47000 J/m2) in comparison to untreated sisal reinforced polyester composite (24000 J/ m2) because coating increases surface interlocking. Hence, the finding of this study recommends performing acetylation and acrylamide treatment on fibres to improve the mechanical properties of sisal fibre reinforced polyester composites.

Acknowledgments Authors are thankful to Council of Scientific and industrial Research (CSIR) India, for permission to carry out the work.

References 1. H. Y. Kim and D. W. Seo, Int. J. Fatigue, 28, 1307 (2006). 2. K. Joseph, S. Thomas, and C. Pavithran, Polymer, 37, 5139 (1996). 3. M. S. Sreekala, M. G. Kumaran, S. Joseph, and M. Jacob, Appl. Compos. Mater., 7, 295 (2000). 4. A. K. Mohanty and M. Misra, Compos. Interface, 8, 313 (2001). 5. K. L. Fung, X. S. Xing, R. K. Y. Li, S. C. Tjong, and Y. W. Mai, Compos. Sci. Technol., 63, 1255 (2003). 6. R. D. T. Filho, F. A. Silva, E. M. R. Fairbarin, and J. A. M. Filho, Const. Build. Mater., 23, 2409 (2009). 7. S. Kalia, B. S. Kaith, and I. Kaur, Polym. Eng. Sci., 49, 1253 (2009). 8. M. Z. Rong, M. Q. Zhang, Y. Liu, G. C. Yang, and H. M. Zeng, Compos. Sci. Technol., 61, 1437 (2001). 9. F. C. Ferreira, A. A. S. Curvelo, and L. H. C. Mattoso, J. Appl. Polym. Sci., 89, 2957 (2003). 10. A. Valadez-Gonzalez, J. M. Cervantes-U, R. Olayo, and P. J. Herrera-Franco, Compos. Pt. B-Eng., 30, 321 (1999). 11. K. Joseph, S. Varghese, G. Kalaprasad, S. Thomas, L. Prasannakumari, P. Koshy, and C. Pavithran, Eur. Polym.,

Ruhi Haque et al.

32, 1243 (1996). 12. K. Joseph, R. D. T. Filho, B. James, S. Thomas, and L. H. Carvalho, Revista Brasileira de Engenharia Agrícola e Ambiental, 3, 367 (1999). 13. P. V. Joseph, M. S. Rabello, L. H. C. Mattoso, K. Joseph, and S. Thomas, Compos. Sci. Technol., 62, 1357 (2002). 14. A. Bismarck, A. K. Mohanty, I. Aranberri-Askargorta, S. Czapla, M. Misra, and G. Hinrichsen, Green Chem., 3, 100 (2001). 15. Y. Li, C. Hu, and Y. Yu, Compos. Pt. A-Appl. Sci. Manuf., 39, 570 (2006). 16. T. H. D. Sydenstricker, S. Mochnaz, and S. C. Amico, Polym. Test, 22, 375 (2003). 17. P. A. Sreekumar, K. Joseph, G. Unnikrishnan, and S. Thomas, Compos. Sci. Technol., 67, 453 (2007). 18. S. Mishra and J. B. Naik, Poly.-Plast. Technol. Eng., 44, 511 (2005). 19. A. R. Martin, S. Monolache, L. H. C. Mattoso, R. M. Rowell, and F. Denes, “Proc. Third Internatl. Symposium on Natural Polymers and Composites”, pp.431-436, Brazil, 2000. 20. H. Djidjelli, A. Boukerrou, R. Founas, A. Rabouhi, M. Kaci, J. Farenc, J. Martinez-Vega, and D. Benachour, J. Appl. Polym. Sci., 103, 3630 (2007). 21. D. N. Saheb and J. P. Jog, Adv. Polym. Tech., 18, 351 (1999). 22. I. O. Oladele, J. A. Omotoyinbo, and J. O. T. Adewara, J. Min. Mat. Charac. Eng., 19, 569 (2010). 23. K. C. M. Nair, S. M. Diwan, and S. Thomas, J. Appl. Polym. Sci., 60, 1483 (1996). 24. A. Leao, “Proc. Internatl. Conf. on Frontiers of Polymers and Advanced Materials”, pp.755-760, Egypts, 1999. 25. Y. Li and Y. Wi, Compos. Sci. Technol., 60, 2037 (2002). 26. A. Valadez-Gonzalez, J. M. Cervantes-U, R. Olayo, and P. J. Herrera-Franco, Compos. Pt. B-Eng., 30, 309 (1999). 27. F. C. Ferreira, A. A. S. Curvelo, and L. H. C. Mattoso, J. Appl. Polym. Sci., 89, 2957 (2003). 28. J. B. Zhong and J. L. C. Wei, Express Polym. Lett., 1, 681 (2007). 29. A. K. Mohanty, M. Misra, and L. T. Drzal, “Natural Fibers, Biopolymers and Biocomposites”, CRC Press, 2005. 30. L. Y. Mwaikambo and M. P. Ansel, “Proc. Internatl. Wood and Natural Fibre Composites”, pp.1211-1216, Kassel, 1999. 31. J. D. Megiatto, W. Hoareau, C. Gardrat, E. Frollini, and A. Castellan, J. Agric. Food Chem., 55, 8576 (2007). 32. F. D. A. Silva and R. D. T. Filho, “Proc. CBM-CI”, p.575, Pakistan, 1996.