Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process

Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process Anshu Anjali Singh*, Kishor Biswas, Dinesh, Priyanka and Sanjay Palsule Department of Polymer & Process Engineering, Indian Institute of Technology-R, IIT-R SRE Campus, Paper Mill Road, Saharanpur 247 001, India Received: 1 August 2014, Accepted: 29 August 2014 Summary Coconut fiber (CNF) reinforced high density polyethylene (HDPE) composites have been processed using maleic anhydride grafted high density polyethylene as compatibilizers by twin extrusion and injection moulding. Successful formation of the CNF/HDPE composites evident from increasing mechanical properties of composites with increasing CNF in them appears to have resulted from good fiber/matrix interfacial adhesion in CNF/HDPE composites due to the use of 1.2% maleic anhydride grafted high density polyethylene (MA-g-HDPE) as a compatibilizers. Mechanical properties of the composites decrease after moisture absorption. INTRODUCTION Natural fiber reinforced polymer composites are emerging as new eco-friendly polymeric composite materials and are offering commercial and engineering applications and techno-economic advantages, like, low price, low density, acceptable specific strength and specific stiffness, reduced tool wear and nonabrasiveness [1, 2]. These composites are environmentally friendly and reduce dependence on non-renewable sources, reduce pollutant and greenhouse gas emissions and also carbon dioxide sequestration, and offer enhanced energy recovery. The unlimited supply, easy availability and presence of cellulose imparting good mechanical properties to natural fibers is promoting natural fiber reinforced polymer composites [3]. *e-mail <anshuanjaliiitr@gmail.com> Smithers Information Ltd., 2014 Applied Polymer Composites, Vol. 2, No. 3, 2014 167

Anshu Anjali Singh, Kishor Biswas, Dinesh, Priyanka and Sanjay Palsule Several natural fibres have been used to develop polymer matrix-based composites, and these include, jute, hardwood, bamboo, banana, sisal, etc. However, of all these natural fibres, coir or coconut fibers contain least amount of celluloses but highest percentage of lignin that provides rigidity to the coconut fibers (CNF) [4]. Reviews on CNF reinforced polymer composites have also been also reported [5, 6]. The presence of cellulose makes natural fibers hydrophilic adversely affecting the adhesion with hydrophobic polymer matrix in the composite and thereby reducing load transfer from matrix to fiber in composite and limiting the mechanical properties of composites. Following three methods have been used to improve the fiber/matrix interfacial adhesion in natural fiber/ polyolefin composites: (i) chemical or physical treatment for surface modification of natural fibers and (ii) use of compatibilizers or coupling agent as third component and (iii) Palsule process of using chemically functionalized polyolefin as matrix. CNF treated using alkali (NaOH), dodecane bromide and silane coupling agent 3-(trimethoxysilyl) propylamine [7]; hydrogen peroxide and (2-4%) NaOH [8]; stearic acid [9] have been used to process treated CNF/HDPE composites. Composites based on chemically functionalized high density polyethylene CNF/CF-HDPE composites have been developed by Palsule process [10]. However, to the best of our knowledge no work has been reported on the use of compatibilizer to process coconut fiber reinforced high density polyethylene composite. Accordingly, this study develops 10/90, 20/80 and 30/70 coconut fiber (CNF) reinforced high density polyethylene (HDPE) composite by using 2% maleic anhydride grafted high density polyethylene (MA-g-HDPE) as a compatibilizer. EXPERIMENTAL Materials Reinforcing coconut fibers obtained from the local market in raw form were chopped to 4-5 mm length and were used, as received, without any fiber surface treatment. Coconut fibers have been termed as CNF. High Density Polyethylene was obtained commercially (RELENE F 46003) from Reliance Industry Limited, India has been used as matrix. It is available, commercially, as free flowing granules and has a reported density of 0.946 g/cm 3, and reported melt flow index (MFI) of 0.30 g/10 min (190 C, 2.16 Kg). Maleic anhydride grafted high density polyethylene (HDPE with 1.2% maleic anhydride grafted on it) used as a compatibilizer in this study was OPTIM E-156 obtained from Pluss Polymer Pvt. Ltd., and is termed as MA-g-HDPE. 168 Applied Polymer Composites, Vol. 2, No. 3, 2014

Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process Compounding and Processing High density polyethylene (HDPE), maleic anhydride grafted high density polyethylene (MA-g-HDPE) and 4-5 mm short reinforcing coconut fibers (CNF) were dried in hot air oven at 50 C for one day, and then at 60 C for 4 hours, prior to extrusion to remove moisture. Table 1 records the formulations of the composites developed in this study. Calculated amounts of HDPE matrix, MA-g-HDPE and reinforcing CNF were mixed manually with a view to finally obtain 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites. Mixtures with appropriate amounts of constituent materials were then fed into the hopper of the co-rotating twin screw extruder (model JSW TEX 30α). The screw speed of the co-rotating twin screw extruder was set at 125 rpm and the temperature profile for nine different zones in the extruder was varied from 145 C to 165 C. The CNF/HDPE/MA-g-HDPE mixtures, with appropriate amounts of the CNF, HDPE and MA-g-HDPE were compounded in the extruder, and the extruded composite compositions, termed as 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites, were cooled in water. Table 1. Formulations of coconut fiber reinforced compatibilized high density polyethylene composite (in weight%) CNF/HDPE/ MA-g-HDPE Composites 0/100/0 10/88/2 Coconut Fiber (CNF) wt% 0 10 High Density Polyethylene (HDPE) wt% 100 88 Maleic Anhydride Grafted High Density Polyethylene (MA-g-HDPE) wt% 0 2 20/78/2 20 78 2 30/68/2 30 68 2 These were then pelletized in a pelletizer to obtain granules that were dried in hot air oven at 60 C for overnight, and were then used to mold test specimens for tensile and flexural tests. To process samples for testing and characterization, as per ASTM standards, HDPE matrix and extruded and pelletized CNF/HDPE/MA-g-HDPE composite granules were molded by using injection molding machine (Electronica ENDURA 90) with the feed zone temperature of 165 C and nozzle temperature of 170 C. Applied Polymer Composites, Vol. 2, No. 3, 2014 169

Anshu Anjali Singh, Kishor Biswas, Dinesh, Priyanka and Sanjay Palsule Testing and Characterization of the CNF/HDPE/MA-g-HDPE Composite Mechanical Properties of the CNF/HDPE/MA-g-HDPE Composite Mechanical properties of the HDPE matrix and the processed 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites have been evaluated following ASTM D638 and ASTM D790 test methods to study the tensile and flexural properties respectively. Both the tensile tests and the three-point bending flexural tests were performed on a Universal Testing Machine, (Model 3382, INSTRON 25 Ton Capacity). The cross head speed for tensile test was 50 mm/min and that for flexural test was 1.36 mm/min. Five samples of HDPE matrix and five samples of each of the 10/88/2, 20/78/2 and 30/68/2 CNF/ HDPE/MA-g-HDPE composites compositions were tested for evaluation of mechanical properties and the results have been recorded as an average of five values. Water Absorption and Mechanical Properties of Wet Samples of CNF/ HDPE/MA-g-HDPE Composite Water absorption tests for HDPE matrix and 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites were conducted in accordance with ASTM D 570. Long-term tests for water absorption at room temperature for 2400 hours were performed for three samples of the HDPE and three samples of each of the 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composite compositions. The samples were placed in distilled water, in a container at room temperature, after conditioning, for which, the samples were dried in an oven at 80 C for 1 hour and were then allowed to cool to room temperature in desiccators. Samples were weighed to the nearest of 0.1 mg. The samples were then immersed in distilled water at room temperature for different time durations. The change in weight of each sample was measured periodically; and then the sample was again submerged in distilled water. Before taking weight, the sample was removed from water and all surface water was wiped with a clean dry cloth. The weight of the sample was measured at different time intervals up to 2400 hours and percent water absorption (WA) and was calculated according to the given following formula: Wt. after immersion time t-conditioned wt. Water absorption(%)= 100 Conditioned wt. (1) Tensile test of the water immersed samples of the HDPE and the processed 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites have 170 Applied Polymer Composites, Vol. 2, No. 3, 2014

Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process been performed following ASTM D 638 standards to evaluate the tensile properties (like the dry samples), to study the influence of water content on the mechanical properties of CNF/HDPE/MA-g/HDPE composites. RESULTS AND DISCUSSIONS Mechanical Characterization of CNF/HDPE/MA-g-HDPE Composites Mechanical properties of a composite material are governed by properties of the matrix, aspect ratio (length/diameter) and amount of the reinforcing fiber, and interfacial adhesion between the matrix and the reinforcing fiber. In this study, tensile and flexural properties of the HDPE matrix and all the compositions of the CNF/HDPE/MA-g-HDPE composites have been evaluated. Five samples of HDPE matrix and five samples of each of the CNF/HDPE/MAg-HDPE composite compositions were tested for evaluation of mechanical properties, and results have been recorded as an average of five values. Tensile Properties Figure 1 indicates the increase in tensile modulus and tensile strength of CNF/HDPE/MA-g-HDPE composites with increasing fiber content in them. In absolute terms, 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE Figure 1. Tensile modulus and tensile strength of CNF/HDPE/MA-g-HDPE composites Applied Polymer Composites, Vol. 2, No. 3, 2014 171

Anshu Anjali Singh, Kishor Biswas, Dinesh, Priyanka and Sanjay Palsule composites respectively have a tensile modulus of 0.32 GPa, 0.37 GPa and 0.41 GPa; that are higher than the tensile modulus of HDPE matrix that has a value 0.27 GPa. In relative terms, compared to the modulus of the HDPE matrix, the tensile modulus of 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/ MA-g-HDPE composites compositions are higher by 18%, 37% and 52% respectively. Similarly, in absolute terms 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g- HDPE composites respectively have tensile strength of 27.58 MPa, 29.97 MPa and 32.24 MPa; that are higher than the tensile strength of CF-PP matrix that has a value of 25.00 MPa. Moreover in relative terms, compared to the tensile strength of the CF-PP matrix, the tensile strength of 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites compositions is higher by 10%, 20% and 29% respectively. Flexural Properties Figure 2 shows the flexural modulus and flexural strength values of HDPE, and of the 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites and indicates the increase in flexural modulus and flexural strength of CNF/ HDPE/MA-g-HDPE composites with increasing fiber content in them. In absolute terms, the 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites respectively have a flexural modulus of 0.81 GPa, 0.89 GPa and 0.97 GPa; that are higher than the flexural modulus of CF-PP matrix that has a value of 0.7 GPa. In relative terms, compared to the flexural modulus of Figure 2. Flexural modulus and flexural strength of CNF/HDPE/MA-g-HDPE composites 172 Applied Polymer Composites, Vol. 2, No. 3, 2014

Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process CF-PP matrix, the flexural modulus of 10/90, 20/80 and 30/70 CNF/CF-PP composite compositions are higher by 16%, 27% and 38% respectively. Similarly, in absolute terms, 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MAg-HDPE composites respectively have a flexural strength of 32.54 MPa, 34.68 MPa and 35.73 MPa; that are higher than the flexural strength of HDPE matrix that has a value of 29.00 MPa. In relative terms, compared to the flexural strength of HDPE matrix, the flexural strength of 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composite compositions are higher by 12%, 19% and 23% respectively. Mechanical properties of the CNF/HDPE/MA-g-HDPE composites indicate that with the increasing amounts of coconut fibers in the CNF/HDPE/MAg-HDPE composite compositions, the tensile and flexural properties of the composites increase relative to that of the HDPE matrix and this establishes the successful formation of the CNF/HDPE/MA-g-HDPE composites. This successful formation of the CNF/HDPE/MA-g-HDPE composites appears to have resulted from good fiber/matrix interfacial adhesion in CNF/HDPE composites due to the use of 1.2% maleic anhydride grafted high density polyethylene (MA-g-HDPE) as a compatibilizer Effect of Fiber Loading on Water Absorption The long term water absorption (WA) by HDPE matrix and by the 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites was monitored by completely immersing the samples in distilled water for 2400 hours (100 days). Hydrophilic property of CNF is responsible for the water absorption in the CNF/HDPE/MA-g-HDPE composites. Water absorption of the CNF/HDPE/ MA-g-HDPE composite compositions is much higher than that of the HDPE matrix and increases with increasing fiber content in composite compositions. 10/88/2 and 20/78/2 CNF/HDPE/MA-g-HDPE composites show less water absorption as compared to the 30/68/2 CNF/HDPE/MA-g-HDPE due to more amount of CNF in the 30/68/2 CNF/HDPE/MA-g-HDPE composite. The maximum percentage weight gains by HDPE and 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites after immersion in distilled water at room temperature for 2400 hours were 0.257%, 0.543%, 0.825% and 1.543% respectively. The water uptake behavior of all CNF/HDPE/MAg-HDPE composites compositions is linear in the beginning and then slows down, but this behavior is not exhibited by the HDPE matrix. When CNF content increases in the composites, the number of free OH groups on CNF also increases, and these OH groups form hydrogen bonds with water and thereby absorb water, and that results in weight gain by the composite. Applied Polymer Composites, Vol. 2, No. 3, 2014 173

Anshu Anjali Singh, Kishor Biswas, Dinesh, Priyanka and Sanjay Palsule Figure 3. Maximum water absorption by CNF/HDPE/MA-g-HDPE composites after 2400 hours Effect of Water Absorption on Mechanical Properties of CNF/HDPE/ MA-g-HDPE Composite Figure 4 represents the tensile modulus and tensile strength for both dry and wet (water immersed for 2400 hours) samples of HDPE and 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites respectively. Figure 4. Effect of water absorption on tensile properties of CNF/HDPE/MA-g-HDPE composites after 2400 hours of immersion 174 Applied Polymer Composites, Vol. 2, No. 3, 2014

Coconut Fiber Reinforced High Density Polyethylene Composites By Compatibilizer Process Tensile modulus and tensile strength of wet (water immersed) samples of HDPE matrix and 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE were found to be lesser than those of their respective dry samples. Studies on tensile modulus of wet HDPE and wet CNF/HDPE/MA-g-HDPE composite compositions indicate that with the amount of fibers in the wet composites increasing from 10% to 20% to 30%, the tensile modulus of the wet 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites decreases by 6%, 9% and 14% respectively, as compared to that of the dry sample of the same composite composition. However, in absolute terms, the tensile modulus of the wet 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites were 0.30 GPa, 0.34 GPa and 0.0.36 GPa respectively that are lower than tensile modulus of 0.32 GPa, 0.37 GPa and 0.41 GPa of dry sample of 10/88/2, 20/78/2 and 30/68/2 CNF/ HDPE/MA-g-HDPE composites respectively. Similarly the studies on tensile strength of wet HDPE and wet CNF/HDPE/ MA-g-HDPE composite compositions indicate that with the amount of fibers in the composites increasing from 10% to 20% to 30%, the tensile strength of the 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites decreases by 10%, 14% and 18% respectively, as compared to that of the dry sample of the same composite composition. However, in absolute terms, the tensile strength of the wet 10/88/2, 20/78/2 and 30/68/2 CNF/ HDPE/MA-g-HDPE composites were 25.00 MPa, 26.37 MPa and 27.34 MPa respectively that are lower than the tensile strengths of 27.58 MPa, 29.97 MPa and 32.24 MPa of dry 10/88/2, 20/78/2 and 30/68/2 CNF/HDPE/MA-g-HDPE composites respectively. This study shows that the tensile properties of the composites are adversely affected by moisture absorption and water uptake by natural fiber reinforced polymer composites, like the CNF/HDPE/MA-g-HDPE composites because water adversely affects the fiber/matrix interfacial adhesion in the composite. In natural fiber/polymer composites these cracks arises due to swelling of the natural fibers. Plant fibers swell due to moisture/water absorption and forms voids at the fiber/matrix interface, creates cracks in the polymeric matrix, reduce load transfer from matrix to fiber in the composite and reduce mechanical properties and dimensional stability. CONCLUSIONS Maleic anhydride grafted high density polyethylene with 1.2% grafting works efficiently as a compatibilizers for coconut fiber (CNF) reinforced high density polyethylene (HDPE) composites. Composites processed by twin extrusion Applied Polymer Composites, Vol. 2, No. 3, 2014 175

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