Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process

Transcription

1 Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process Anshu Anjali Singh and Sanjay Palsule* Department of Polymer & Process Engineering, Indian Institute of Technology, IIT-R SRE Campus, Paper Mill Road, Saharanpur India Received: 3 June 2014, Accepted: 9 November 2014 Summary 10/90, 20/80 and 30/70 CNF/CF-HDPE Coconut fibre (CNF) reinforced chemically functionalized high density polyethylene composites developed by Palsule process were immersed in distilled water at room temperature for 6600 hours. The amount of water absorbed by the CNF/CF-HDPE composites immersed in the water, increases with increasing amounts of the reinforcing coconut fibers in the composites. Tensile modulus and tensile strength of the water absorbed wet CNF/CF-HDPE composites are lower than those of the dry composites; but are higher than the dry and wet CF-HDPE matrix. Introduction Natural fibre reinforced polymer composites are offering several technoeconomic and environmental advantages, and are replacing conventional synthetic or inorganic fibre reinforced polymer composites in some applications. Hydrophilic natural fibres have poor compatibility with hydrophobic thermoplastic polymer matrix in a natural fibre reinforced polymer composite. Consequently, the weak fibre/matrix interfacial adhesion in natural fibre reinforced thermoplastic polymer composites limits proper load transfer from the matrix to the fibre and limits the mechanical and other properties of the *macrofpt@gmail.com, macrofpt@iitr.ac.in Smithers Information Ltd., 2014 Applied Polymer Composites, Vol. 2, No. 4,

2 Anshu Anjali Singh and Sanjay Palsule composites. Therefore, following three processes have been used to improve fibre/matrix interfacial adhesion in natural fibre reinforced thermoplastic composites: (i) Modification of Natural Fibre process (ii) Compatibilizer process; and (iii) Palsule process based on self compatibilizing polyolefin matrix, in place of polyolefin. Several studies reported on water absorption behaviour of natural fibre reinforced polymer composites indicate that properties of natural fibre reinforced polymer composites are adversely affected as the composites absorb moisture when exposed to humid atmosphere or when immersed in water [1-7]. Three different mechanisms have been indicated in literature for water absorption by polymeric composite materials [2, 4, 8]. These are: (i) diffusion of water molecules inside the micro gaps in the polymer matrix, (ii) water absorption via capillary transport into the gaps, and (iii) transport of water molecules through micro cracks formed during the processing of the composite [2, 4, 8]. Several factors influence water absorption by a natural fibre reinforced polymer composites, including; volume fraction of fibres, viscosity of matrix, voids, humidity and temperature. A review on moisture absorption by natural fibre reinforced polymer composites has also been reported [8]. This study deals with the water absorption behaviour and its effect on the mechanical properties of coconut fibre reinforced self compatibilizing high density polyethylene (CNF/CF-HDPE) composites developed by Palsule process [9]. Processing and structure and properties of these CNF/CF-HDPE composites have been reported in literature [9]. Experimental Materials (a) Matrix Polymer In this study, chemically functionalized high density polyethylene (CF-HDPE) with 1.2% maleic anhydride grafted on it, has been used as matrix for the composites. CF-HDPE was obtained commercially (OPTIM E-156, Series 300) from Pluss Polymer Pvt. Ltd., India. It is available, as free flowing granules and is off white to light yellow in appearance. It has a reported density of g/cm 3, reported melting temperature (T m ) of 132 C and the melt flow index (MFI) of 4.5 g/10 min (190 C, 2.16 kg). 230 Applied Polymer Composites, Vol. 2, No. 4, 2014

3 Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process (b) Reinforcing Fibre Reinforcing coconut fibres, of 0.06 mm average diameter, obtained from the local market in raw form, were chopped to 3-5 mm length and were used, as received, without any fibre surface treatment. Coconut fibres have been termed as CNF. Compounding and Processing of CNF/CF-HDPE Composites Chemically functionalized high density polyethylene (CF-HDPE), and 3-5 mm short coconut fibres (CNF) were dried in hot air oven at 50 C for one day, and then at 80 C for 3-4 hours, prior to extrusion to remove the moisture. Table 1 records the formulations of the CNF/CF-HDPE composites developed in this study. Calculated amounts of CNF and CF-HDPE matrix were mixed manually with a view to finally obtain 10/90, 20/80 and 30/70 CNF/CF-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 JSW TEX 30α co-rotating twin-screw extruder was set at 145 rpm and the temperature profile for nine different zones in the extruder was varied from 155 C to 175 C. In particular, the temperature profiles of the various zones of the extruder for processing CNF/CF-HDPE composites were C C C C C C C -175 C C. Table 1. Formulations of coconut fibre reinforced chemically functionalized high density polyethylene (CNF/CF-HDPE) composites (in weight %) CNF/CF-HDPE Composites 0/100 10/90 Coconut Fibre (CNF) (Wt%) 0 10 Chemically Functionalized- High Density Polyethylene (CF-HDPE) (Wt%) / / The CNF/CF-HDPE mixtures, with appropriate amounts of the CNF and CF-HDPE, were compounded in the extruder, and the extruded composite compositions, termed as 10/90, 20/80 and 30/70 CNF/CF-HDPE composites, were cooled in water. These were then pelletized in a pelletizer to obtain granules that were dried in hot air oven at 80 C for overnight, and were then used to mold test specimens. To process samples for testing and characterization, as per ASTM standards, CF-HDPE matrix and extruded and pelletized CNF/ Applied Polymer Composites, Vol. 2, No. 4,

4 Anshu Anjali Singh and Sanjay Palsule CF-HDPE composite granules were molded by using injection molding machine (Electronica ENDURA 90), with the feed zone temperature of 145 C and nozzle temperature of 170 C. Water absorption by the composites and the effects of absorbed water on mechanical properties of 10/90, 20/80 and 30/70 CNF/CFHDPE composites have been evaluated as per ASTM standards using the state of the art equipment, as described in the following sections. Testing and Characterization of CNF/CF-HDPE Composite Water Absorption In this study water absorption test for the CF-HDPE matrix and the processed CNF/CF-HDPE composites, have been conducted in accordance with ASTM D 570. To weigh the samples, an analytical balance capable of reading g was used. An oven, capable of maintaining uniform temperature of 50±3 C and of 105 to 110 C was also used to condition the samples. Dumbbell shaped specimen (similar to the one used for tensile tests) of the CF-HDPE matrix and CNF/CF-HDPE composites are used for the measurements of water absorption. For conditioning, the samples were dried in an oven at 80 C for 1 hour, cooled to room temperature in a desiccator, and immediately weighed to the nearest g. The conditioned samples were immersed in distilled water in a container maintained at room temperature. At different time interval, the samples were removed from water, wiped with a dry cloth and immediately weighed to the nearest of g, and then replaced in water. The weighing of the samples is repeated at a regular interval until the specimens achieve considerable saturation. Percent water absorption (%WA) was calculated as follows: %Water absorption = Weight of the sample after immersion time t - Conditioned weight of sample x 100 Conditioned weight of sample Tensile Testing of Dry and Wet Sample In this study, the tensile properties of dry and wet CF-HDPE matrix and the processed CNF/CF-HDPE composites were evaluated by a Universal Testing Machine (UTM), (Model 3382, INSTRON, 100 kn Capacity) as per ASTM D638. In this study, the crosshead speed for the testing of the sample was set at 50 mm/min. 232 Applied Polymer Composites, Vol. 2, No. 4, 2014

5 Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process Results and Discussions Water Absorption by CNF/CF-HDPE Composites Natural fibre reinforced polymer composites absorb moisture when immersed in water or exposed to humid atmosphere. Water absorption by CF-HDPE matrix and 10/90, 20/80 and 30/70 CNF/CF-HDPE composites was measured in accordance with ASTM D 570. Effect of Coconut Fibre Content on Water Absorption by CNF/CF- HDPE Composites Water absorption (WA) by CF-HDPE matrix and by 10/90, 20/80 and 30/70 CNF/ CF-HDPE composites processed in this study, was monitored by completely immersing the samples in distilled water for 6600 hours at room temperature. Three samples of CF-HDPE and three samples of each of the 10/90, 20/80 and 30/70 CNF/CF-HDPE composite compositions were evaluated for water absorption and their average has been recorded. Figure 1 shows percentage water absorption (WA%) by the CF-HDPE and by the different compositions of the CNF/CF-HDPE composites at different time interval, at room temperature. In the beginning the rate of water absorption by the materials was higher but as the number of days increased the samples started approaching saturation and the change in the weight due to water absorption was either very less or negligible. Figure 1. Water absorption of the CF-HDPE matrix and different compositions of the CNF/CF-HDPE composites at different time interval and at room temperature Applied Polymer Composites, Vol. 2, No. 4,

6 Anshu Anjali Singh and Sanjay Palsule The initial rate of water absorption and the maximum water uptake increases for all the CNF/CF-HDPE composite compositions with increase in the fibre content in the composite compositions. Hydrophilic property of coconut fibre is responsible for the water absorption in the CNF/CF-HDPE composites. When the coconut fibre content increases in the CNF/CF-HDPE composites, the number of free OH groups also increases, and these OH groups form hydrogen bonds with water and thereby absorb water. The water uptake behaviour of all CNF/CF-HDPE composite compositions is linear in the beginning and then slows down, but this behaviour is not exhibited by the CF-HDPE matrix. Figure 2 shows that the maximum water absorption (%) by 10/90, 20/80 and 30/70 CNF/CF-HDPE composites, after immersion in distilled water at room temperature for 6600 hours is approximately 1.33%, 2.22% and 4.31% respectively. Thus, least amount of water is absorbed by 10/90 CNF/CF-HDPE that has the least amount of CNF, the highest amount of water is absorbed by 30/70 CNF/CF-HDPE composite that has the maximum amount of reinforcing CNF in this study and the 20/80 CNF/ CF-HDPE composite absorbs intermediate amount of water. Figure 2. Maximum water absorption (%) by CF-HDPE matrix by CNF/CF-HDPE composites at room temperature, after 6600 hours Effect of Water Absorption on Tensile Properties of CNF/CF-HDPE Composite Table 2 shows the tensile modulus and tensile strength recorded as per ASTM D 638 as an average of three samples of wet CF-HDPE and three samples of the wet 10/90, 20/80 and 30/70 CNF/CF-HDPE composite compositions after immersion in water. Table 2, Figure 3 and Figure 4 show, respectively, the tensile modulus and the tensile strengths of both dry and wet samples 234 Applied Polymer Composites, Vol. 2, No. 4, 2014

7 Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process (after immersion in water for 6600 hours) of CF-HDPE and 10/90, 20/80 and 30/70 CNF/CF-HDPE composites. Table 2. Tensile properties of water immersed samples of CF-HDPE matrix and CNF/CF-HDPE composites Materials Tensile Modulus Tensile Strength Average Value (GPa) Standard Deviation Average Value (MPa) Standard Deviation Wet CF-HDPE Wet 10/90 CNF/CF-HDPE Wet 20/80 CNF/CF-HDPE Wet 30/70 CNF/CF-HDPE Figure 3. Tensile modulus of dry and wet samples of CNF/CF-HDPE composites Figure 4. Tensile strength of dry and wet CNF/CF-HDPE composites Applied Polymer Composites, Vol. 2, No. 4,

8 Anshu Anjali Singh and Sanjay Palsule Tensile modulus and tensile strength of wet (water immersed) samples of CF-HDPE matrix and 10/90, 20/80 and 30/70 CNF/CF-HDPE were found to be lesser than those of their respective dry samples. Studies on tensile modulus of the wet CNF/CF-HDPE composite compositions indicate that in absolute terms, the tensile modulus of the wet 10/90, 20/80 and 30/70 CNF/ CF-HDPE composites were 0.43 GPa, 0.50 GPa and 0.62 GPa respectively that are lower than tensile modulus of 0.50 GPa, 0.62 GPa and 0.81 GPa of dry sample of 10/90, 20/80 and 30/70 CNF/HDPE composites respectively [9]. In relative terms, with the amount of fibres in the composites increasing from 10% to 20% to 30%, the tensile modulus of the wet 10/90, 20/80 and 30/70 CNF/CF-HDPE composites decreases by 16%, 24% and 31% respectively, as compared to that of the dry sample of the same composite composition. However the tensile modulus values of the wet water immersed samples of 10/90, 20/80 and 30/70 CNF/CF-HDPE composites are higher than the tensile modulus (0.41 GPa) of the dry CF-HDPE matrix [9]; and also higher than the tensile modulus of the wet CF-HDPE (0.38 GPa). Similarly the studies on tensile strength of wet CNF/CF-HDPE composite compositions indicate that, in absolute terms, the tensile strength of the wet 10/90, 20/80 and 30/70 CNF/CF-HDPE composites were MPa, MPa and MPa respectively that are lower than the tensile strengths of MPa, MPa and MPa of dry 10/90, 20/80 and 30/70 CNF/HDPE composites respectively [9]. In relative terms, with the amount of fibres in the composites increasing from 10% to 20% to 30%, the tensile strength of the wet 10/90, 20/80 and 30/70 CNF/CF-HDPE composites decreases by 4%, 12% and 13% respectively, as compared to that of the dry sample of the same composite composition. However the tensile strength values of the wet water immersed samples of 10/90, 20/80 and 30/70 CNF/CF-HDPE composites are higher than those of the tensile strength (22.83 MPa) of the dry CF-HDPE [9] and also higher than the tensile strength of the wet CF-HDPE (20.58 MPa). This study shows that the tensile properties of the CNF/CF-HDPE composites are adversely affected by moisture absorption and water uptake. Conclusions 10/90, 20/80 and 30/70 CNF/CF-HDPE - Coconut fibre (CNF) reinforced functionalized self compatibilizing high density polyethylene (CF-HDPE) composites developed by Palsule process absorb significant amount of water when immersed in distilled water at room temperature for a long duration of 6600 hours. Water absorption by the composite compositions is higher 236 Applied Polymer Composites, Vol. 2, No. 4, 2014

9 Effect of Water Absorption on Coconut Fibre Reinforced Functionalized Polyethylene Composites Developed by Palsule Process than that of the CF-HDPE matrix and increases with increasing fibre content in CNF/CF-HDPE composite compositions. Tensile modulus and tensile strength of the wet CNF/CF-HDPE composite compositions are lower than those of the dry CNF/CF-HDPE composite compositions, but higher than dry CF-HDPE matrix. References 1. Karmaker A.C., Journal of Material Science Letter, 16, , (1997). 2. Espert A., Vilaplana F., and Karlsson S., Composites Part A, 35, , (2004). 3. Yang H.-S., Kim H.-J., Park H.-J., Lee B.-J. and Hwang T.-S., Composite Structures, 72, (2006). 4. Dhakal H.N., Zhang Z.Y., and Richardson M.O.W., Composites Science and Technology, 67(7-8), , (2007). 5. Shakeri A. and Ghasemian A., Applied Composite Materials, 17, (2010). 6. Girisha C., Sanjeevamurthy and Srinivas G.R., International Journal of Engineering and Innovative Technology, 2(3) , (2012). 7. Singh A.A., and Palsule S., Applied Polymer Composites, 1(2), , (2013). 8. Azwa Z.N., Yousif B.F., Manalo A.C., and Karunasena W., Materials and Design, 47 (2013) Singh A.A. and Palsule S., Journal of Composite Materials; 48 (29) (2014). Applied Polymer Composites, Vol. 2, No. 4,

10 Anshu Anjali Singh and Sanjay Palsule 238 Applied Polymer Composites, Vol. 2, No. 4, 2014