Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites

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1 Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites Govardhan Goud 1* and R.N. Rao 2 1 *Department of Mechanical Engineering, Bahubali College of Engineering, Shravanabelagola , Karnataka, India 2 Department of Mechanical Engineering, National Institute of Technology, Warangal , Andhra Pradesh, India Received: 23 January 2013, Accepted: 16 April 2013 Summary Effect of fiber content and combined effect of alkali and silane coupling agent treatments on tensile and impact properties of unidirectional roystonea regia natural fiber reinforced epoxy based partially bio degradable composites is reported. The reinforcement roystonea regia fiber was collected from the foliage of royal palm tree. To overcome the problems of poor fiber/matrix interface bonding, alkali and silane treatments have been applied to fibers to process the composites. Alkali treatment has been found to be more effective in improving the tensile properties than the silane treatment; however mixed treatment further slightly improved the properties. In general, the impact strength of all the treated fiber composites decreased compared to the untreated fiber composites; however, the silane treated fiber composites have shown higher impact strength followed by alkali treated fiber composites. Morphology of composites examined by scanning electron microscopy has also been reported. Keywords: Roystonea regia fiber, Epoxy matrix, Alkali treatment, Silane treatment, Natural fiber epoxy composites 1 Corresponding author. pgovardhan0@yahoo.com; Fax: Smithers Rapra Technology, 2013 Applied Polymer Composites, Vol. 1, No. 3,

2 Govardhan Goud and R.N. Rao INTRODUCTION Natural fibers as reinforcement offer several advantages such as low cost, high specific strength, eco friendliness, and easy dispersion in polymer matrices, low density and biodegradability [1]. Low density of the natural fibers attracted the scientists to consider them as an alternative reinforcement to the glass fibers in many applications. Few natural fibers are already in vogue as reinforcement in polymer matrices [2-6]. Poor compatibility between hydrophilic natural fiber and hydrophobic polymer matrix poses severe problems in their manufacturing. In this regard treatments with alkali solution and silane coupling agents have been proved to be the best methods to strengthen the fiber/matrix interaction in natural fiber/polymer composites. Alkali solution and silane coupling agent treatments have been used to strengthen the fiber/matrix interactions in natural fiber polymer composites. Alkali treatments improved flexural properties of jute fiber reinforced unsaturated polyester composites [7]. 15% increase in tensile strength after alkali treatment of unidirectional sisal reinforced epoxy composites has also been reported [8]. Valadez-Gonzalez et al. investigated the effect of fiber surface treatment by dilute NaOH aqueous solution on the fiber-matrix bond strength of henequen natural fiber reinforced high density polyethylene composites and found improvement in bond strength [9]. Masud et al. reported that surface treated (with NaOH aqueous solution and silane coupling agent) kenaf fiber reinforced poly lactic acid (PLA) composites show superior mechanical properties than untreated fiber reinforced composites [10]. Present work investigates the effect of fiber content in weight percentage and the combined effect of alkali treatment and silane treatment on tensile and impact properties of roystonea regia natural fiber/epoxy composites. MATERIALS AND METHODS Materials The matrix system used is an epoxy resin (Lapox-12) and hardener (k-6) supplied by Atul Limited, Gujarat, India. Fibers were extracted from the foliage of roystonea regia tree. Fiber Extraction From the foliage sheath, the leaves and leaf stem were removed and the sheath was dried for three days in shade. In the next step it was immersed in water 188 Applied Polymer Composites, Vol. 1, No. 3, 2013

3 Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites retting tank for three weeks followed by hand rubbing and rinsing in water till the unwanted greasy material was dissolved and fine fiber was extracted. Alkali Treatment The dry fiber was treated with 5% solution of NaOH for 2 hours to remove the unwanted soluble cellulose, hemi cellulose, pectin, lignin etc. Treatment with Silane Coupling Agent The coupling agent, 3-Amino propyl triethoxy silane was diluted to 1% (v/v) in acetone and the fiber was dipped in diluted coupling agent solution for 1 hour and finally dried at 60 C for 24 hours. Mixed Treatment It is the combination of alkali and silane treatments. Silane treatment was carried out on alkali treated fiber. Composite Preparation A simple hand lay-up technique was used to obtain the composite plates of the size 200 x 150 x 3 mm 3. Tensile Testing of the Composites Tensile testing was performed as per ASTM D with the help of INSTRON-3369 model Universal Testing Machine. The specimen dimensions were 150 x 15 x 3 mm 3. Average of five tests was recorded. Izod Impact Tests of the Composites Izod Impact tests were performed as per ASTM D standard by Izod impact machine (Ceast model 6545) manufactured by Ceast Company, Italy with unnotched specimen. The specimen dimensions were 122 x 13 x 3 mm 3. The pendulum impact testing machine ascertains the impact strength of the material by shattering the specimen with a pendulum hammer, measuring the spent energy and relating it to the cross section of the specimen. Falling Applied Polymer Composites, Vol. 1, No. 3,

4 Govardhan Goud and R.N. Rao weight on a pendulum strikes a cantilevered sample. Results were recorded as average of five samples. RESULTS AND DISCUSSION Tensile Strength of Untreated and Treated Composites Tables 1-3 list the tensile properties of the composites. From Tables 1-3 and Figures 1, 2 and 3 it is evident that with the increase in fiber content in Table 1. Tensile strength of untreated and treated composites at different fiber contents Composite Tensile strength(mpa) at fiber content(%wt) 0% 5% 10% 15% 20% UT AT ST AT+ST Table 2. Tensile modulus of untreated and treated composites at different fiber contents Composite Tensile modulus(mpa) at fiber content(%wt) 0% 5% 10% 15% 20% UT AT ST AT+ST Table 3. Percentage elongation at break of untreated and treated composites at different fiber contents Composite Percentage elongation at fiber content(%wt) 0% 5% 10% 15% 20% UT AT ST AT+ST Applied Polymer Composites, Vol. 1, No. 3, 2013

5 Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites composite compositions, there is an increase in tensile strength, tensile modulus and % elongation at break for both treated and untreated fiber composites indicating improved fiber/matrix interfacial adhesion due to surface treatment of fibers. When compared with the neat epoxy (0% fiber content), tensile strength and tensile modulus of 5% and 10% fiber composites are low. This is due to the lower fiber loading acting as flaws in the matrix. Figure 1. Tensile strength of untreated and treated composites at different fiber contents. Figure 2. Tensile modulus of untreated and treated composites at different fiber contents. Applied Polymer Composites, Vol. 1, No. 3,

6 Govardhan Goud and R.N. Rao Figure 3. Percentage elongation at break of untreated and treated composites at different fiber contents. UT Untreated; AT Alkali Treated; ST Silane Treated; AT+ST Alkali and Silane Treated The increase in tensile properties of alkali treated fiber composites could be due to the increased interface between matrix and fiber after treatment. The alkali treatment, by removing hemi cellulose and lignin contents from the fiber, yields higher percentage of alpha cellulose in natural fibers [11]. This makes the fiber surface coarser leading to better interface bonding between matrix and fiber. Alkalization also causes fibrillation i.e. breaking of fiber bundles into smaller fibers and that increases the effective surface area available for wetting by the matrix material [12]. Removal of hemicelluloses and lignin creates a larger area of contact between fiber and matrix resulting in enhanced tensile strength [13]. This results in enhanced tensile properties. Silane coupling agent treatment has proved to be effective in reducing the number of cellulose hydroxyl groups in the fiber-matrix interface. In the presence of moisture, silanols are formed and these silanols react with the of the fiber and form stable covalent bonds to the cell wall that are chemisorbed onto the fiber surface. This results in better bonding between fiber and matrix leading to better stress transfer between the matrix and the fiber. The mixed treatment yields the advantages of both alkali and silane treatments. The tensile fractured morphology of untreated and treated fiber composites is shown in Figure 4a-d. The fiber damage is more in untreated fiber reinforced composite (Figure 4a) compared with the treated fiber reinforced composites (Figure 4b-d). The interface bonding of mixed treated fiber composite (Figure 4d) appears to be good among treated fiber composites. Silane 192 Applied Polymer Composites, Vol. 1, No. 3, 2013

7 Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites treated fiber composite (Figure 4c) has shown poor interface compared to alkali treated fiber composite (Figure 4b). (a) (b) (c) (d) Figure 4. Tensile fractured surface of (a) untreated fiber composite, (b) alkali treated fiber composite, (c) silane treated fiber composite, and (d) mixed treated fiber composite (at 20% wt. fiber content) Impact Strength of Untreated and Treated Composites Izod impact test results are shown in Figure 5 and Table 4. From the figure it is evident that though there is an increase in impact strength with increase in fiber loading, the values decreased after treatment. At 20% fiber loading, impact strength of alkali treated fiber composites was decreased by 22%, for silane treated fiber composites impact strength was decreased by 17% and for mixed treated fiber composites impact strength was decreased by 26% when compared with untreated fiber composites. This could be mainly due Applied Polymer Composites, Vol. 1, No. 3,

8 Govardhan Goud and R.N. Rao to the reason that during the impact, considerable part of energy absorption takes place through the fiber pull-out and plastic deformation processes [14] but after treatment strong mechanical inter locking develops between fiber and matrix and fiber pull out and plastic deformation of matrix are minimized. This in turn decreases the impact strength. Mixed treatment of fiber proved to be effective followed by alkali treatment in improving the fiber matrix interface bondage when compared to silane treatment. Figure 5. Impact strength of untreated and treated composites at different fiber contents. UT Untreated; AT Alkali Treated; ST Silane Treated; AT+ST Alkali and Silane Treated Table 4. Impact strength of untreated and treated composites at different fiber contents Composite Impact strength(j/m) at fiber content(%wt) 0% 5% 10% 15% 20% UT AT ST AT+ST Also from Figure 5 it is evident that there is an increase in impact strength with increase in fiber loading and at 20% fiber loading the impact strength is highest. In composites with higher fiber loading, fibers capacity to hold stresses in the matrix before break would be enhanced and it also improves 194 Applied Polymer Composites, Vol. 1, No. 3, 2013

9 Combined Effect of Alkali and Silane Treatments on Tensile and Impact Properties of Roystonea Regia Natural Fiber Reinforced Epoxy Composites the resistance to crack propagation in the matrix. Thus the impact failure of the composite is reduced with the addition of fibers. This is evident from SEM images of impact fractured surfaces as shown in Figure 6a and b. Composite with 20% fiber content (Figure 6b) shows less damage when compared with the composite with 10% fiber content (Figure 6a). (a) (b) Figure 6. Impact fractured surface of (a) composite with 10% wt. fiber content, and (b) composite with 20% wt. fiber content CONCLUSIONS Tensile strength, tensile modulus and % of elongation of untreated and treated roystonea regia natural fiber reinforced epoxy composites were increased with Applied Polymer Composites, Vol. 1, No. 3,

10 Govardhan Goud and R.N. Rao increase in fiber content and are highest at 20% wt. fiber content. Treated fiber composites have shown superior tensile properties than untreated fiber composites. Mixed treatment has found to be effective followed by alkali treatment in enhancing the tensile properties. Impact strength of treated fiber composites was decreased at all fiber contents when compared with the untreated fiber composites. Silane treated fiber composites have shown higher impact strength followed by alkali treated fiber composites. However mixed treated fiber composites have shown poor impact strength. REFERENCES 1. Jayaramudu J., Obireddy K., Uma Maheshwari C., Jeevan Prasad Reddy D. and Varada Rajulu A., Journal of Reinforced Plastics and Composites, 28 (2009) Varma I.K., Anantha Krishnan S.R., and Krishnamurthy S., Composites, 20 (1989) Sridhar M.K., Basavarajappa G., Kasturi G.S., and Balasubramanian N., Indian Journal of Technology, 22 (1984) Roe P.J. and Ansel M.P., Journal of Material Science, 20 (1985) Dhakal H.N., Zhang Z.Y., and Richardson M.O.W., Composite Science and Technology, 67 (2007) Wibowo A.C., Mohanty A.K., Misra M., and Drzal L.T., Industrial and Engineering Chemistry Research, 43 (2004) Sinha E. and Rout S.K., Bulletin of Materials Science, 32 (2009) Min Zhi Rong, Ming Qiu Zhang, Yuan Liu, Gui Cheng Yang and Han Min Zeng, Composites Science and Technology, 61 (2001) Valadez-Gonzalez A., Cervantes-Uc J.M, Olayo R. and Herrera-Franco P.J., Composites: part B, 30 (1999) Huda M.S., Drzal L.T., Mohanty A.K. and Misra M., Composites Science and Technology, 68 (2008) Jayaramudu J., Guduri B.R. and Rajulu A.V., International Journal of Polymer Analysis and Characterization, 14 (2009) Baiardo M., Frisoni G., Scandola M., and Licciardello A., Journal of Applied Polymer Science, 83 (2002) Bisanda E.T.N. and Ansell M.P., Composites Science and Technology, 41 (1991) Pukanszky B. and Maurer F.H.J., Polymer, 36 (1995) Applied Polymer Composites, Vol. 1, No. 3, 2013