Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process

Transcription

1 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process Anshu Anjali Singh and Sanjay Palsule Department of Polymer & Process Engineering, Indian Institute of Technology-R, IIT-R SRE Campus, Paper Mill Road, Saharanpur , India Received: 13 October 2012, Accepted: 18 January 2013 Summary Jute fiber (JF) reinforced chemically functionalized high density polyethylene (CF- HDPE) composites (JF/CF-HDPE) of various compositions (10%, 20% and 30% JF) developed by Palsule process of using modified matrix were immersed in distilled water at room temperature for 6600 hours to study the effect of long term water absorption. Water absorption, thickness swelling, of the composite compositions was higher than that of the CF-HDPE and increased with increasing fiber content in composite compositions. Tensile modulus and tensile strength of the wet composite compositions was lower than that of the dry JF/CF-HDPE composite compositions. Voids, capillary water transport and hydrogen bonds promote water absorption in JF/CF-HDPE composites. Keywords: Jute fiber/chemically functionalized HDPE JF-CFHDPE composite, Palsule Process, Water absorption, Thickness swelling, Tensile properties, Fiber/ Matrix interface, Voids, Capillary water transport, Hydrogen bonds INTRODUCTION Natural fibers, for example, jute, flax, coconut, hemp, sisal etc. are being increasingly used as replacement of conventional fibers (e.g., glass, carbon, aramid), as reinforcers for polymer matrix composites due to their techno- Smithers Rapra Technology, 2013 Applied Polymer Composites, Vol. 1, No. 2,

2 Anshu Anjali Singh and Sanjay Palsule economic advantages, including, low density, good mechanical properties, low cost, and unlimited and easy availability, The environmental advantages of using natural fibers include, renewable and biodegradable nature, problem-free disposal, reduced dependence on non-renewable sources, lower pollutant emissions, lower greenhouse gas emissions, carbon-di-oxide sequestration, enhanced energy recovery, and end of life biodegradability of components [1, 2]. Among all the natural fibers, jute fibers appear to be the most commonly used fibers. Like all other natural fibers, jute fibers are also lingo-cellulosic in nature with more percentage of cellulose than lignin. Presence of lingo-cellulosic components makes jute fibers hygroscopic and thereby incompatible with hydrophobic polyolefin creating poor fiber/matrix interfacial adhesion in natural fiber reinforced polyolefin composites. High moisture absorption by natural fibers due to their hydrophilic nature adversely affects mechanical properties of natural fiber/polyolefin composites and also leads to their poor dimensional stability and low thermal stability [3, 4]. Several studies performed on water absorption by natural fiber/polyolefin composites, and their susceptibility to moisture indicate that properties of natural fiber/polymer composites are adversely affected as the composites absorb moisture when exposed to humid atmosphere or when immersed in water [5-10]. Karmaker et al. [5] investigated the influence of water absorption on mechanical properties of jute fiber-reinforced polypropylene composites. Espert et al. [6] observed decrease in the tensile properties of water absorbed wet wood fiber/polypropylene composites as compared to the dry samples. Dhakal et al. [8] processed hemp fiber reinforced unsaturated polyester composites (HFRUPE) to evaluate the effects of water absorption on their mechanical properties and observed that as the fiber volume fraction increases in the composite compositions, the percentage of moisture uptake increases due to the increased cellulose content. Girisha et al. [10] studied the water absorption behavior and its effect on the mechanical properties of natural fibers (coconut/coir and sisal fibers) reinforced epoxy composites. A review on moisture durability of natural fiber/polymer composites has also been reported [11]. Three different mechanisms have been indicated in literature for water absorption in polymeric composite materials [6, 8, 11]. 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 [6, 8, 11]. Several factors influence water absorption by a natural fiber/polyolefin composites, for example; volume fraction of fibers, viscosity of matrix, voids, humidity and temperature. 114 Applied Polymer Composites, Vol. 1, No. 2, 2013

3 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process In view of poor fiber/matrix interfacial adhesion, following three processes have been used to improve fiber/matrix interfacial adhesion in natural fiber/ polyolefin composites: (i) chemical and/or physical treatment of surface of natural fibers (ii) use of third components i.e; compatibilizer (iii) Palsule process of modified polyolefin matrix. This study describes water absorption behavior and its effects on fiber/matrix interfacial adhesion and tensile properties of jute fiber reinforced chemically functionalized modified polyethylene (JF/ CF-HDPE) composites developed by Palsule process [12-15]. Details of development of JF/CF-HDPE composites by Palsule process have been described in literature [15]. EXPERIMENTAL Materials Jute fibers, termed as JF, used as reinforcer, obtained from the local market in raw form were chopped to 3-6 mm length. Jute fibers mainly contain 64.4% cellulose, 12% hemicelluloses, 11.8% lignin, 0.2% pectin and 0.5% wax [1]. Jute fibers were used as received, and no fiber surface treatment was performed. Polyethylene, that requires a compatibilizer or fiber surface treatment for better fiber/matrix interfacial adhesion in natural fiber/polyethylene composites, was not used as matrix, but chemically functionalized high density polyethylene, with 1.2% maleic anhydride grafted on it (OPTIM E-156, Series 300) obtained from Pluss Polymer Pvt. Ltd., India was used as matrix and has been termed as CF-HDPE. CF-HDPE is available as off white to light yellow colored free flowing granules having densities of gm/ml, melting temperature 132 C and melt flow index (MFI 190 C, 2.16 kg) of 4.5. Compounding and Processing JF and CF-HDPE were dried in an oven at 80 C for 3-4 hrs. Calculated amounts JF and CF-HDPE were mixed manually with a view to finally obtain 10/90, 20/80 and 30/70 JF/CF-HDPE composites. Mixtures with appropriate amounts of JF and CF-HDPE constituents, were fed into the hopper of the co-rotating twin screw extruder (model JSW TEX 30α) having 30 mm screw diameter and L/D ratio of 36:1 and the screw speed was set at 145 rpm. There are nine different temperature zones in TEX 30α extruder and the temperature profile for these zones varies from 155 C to 175 C. The temperature profiles of the various zones of the extruder were C-155 C -160 C-160 C Applied Polymer Composites, Vol. 1, No. 2,

4 Anshu Anjali Singh and Sanjay Palsule -165 C -170 C-175 C-175 C-165 C. The extruded 10/90, 20/80 and 30/70 JF/CF-HDPE composites were cooled in water. These were then pelletized in a pelletizer to obtain granules that were kept in hot air oven at 80 C for overnight and were then used to mold test specimens of 10/90, 20/80 and 30/70 JF/CF-HDPE composites for tensile tests using Electronica ENDURA 90 injection molding machine with feed zone temperature and the nozzle temperature of 145 C and 170 C respectively. Water Absorption and Thickness Swelling Water absorption and thickness swelling tests for CF-HDPE matrix and 10/90, 20/80 and 30/70 JF/CF-HDPE composites were conducted in accordance with ASTM D Long-term tests for water absorption at room temperature for 6600 hours were performed for three samples of the CF-HDPE and three samples of each of the 10/90, 20/80 and 30/70 JF/CF-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 the distilled water at room temperature for different time durations. The change in weight and in thickness 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 6600 hours and both percent water absorption (WA) and percent thickness swelling (TS) were calculated according to the given following formula 1 and 2: wt after immersion time t-conditioned wt Water absorption (%)= x100 conditioned wt thickness after time t-initial thickness Thickness swelling (%)= x100 initial thickness (1) (2) Tensile Testing Tensile tests of the CF-HDPE and the processed 10/90, 20/80 and 30/70 JF/ CF-HDPE composites have been performed following ASTM D 638 standards to evaluate the tensile properties of, both, the dry and water immersed (wet) samples, to study the influence of water content on the mechanical properties 116 Applied Polymer Composites, Vol. 1, No. 2, 2013

5 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process of JF/CF-HDPE composites. Tensile tests were performed on a Universal Testing Machine, (Model 3382, INSTRON 25 Ton Capacity) with crosshead speed of 50 mm/min. RESULTS AND DISCUSSIONS Effect of Fiber Loading on Water Absorption and Thickness Swelling The long term water absorption (WA) and thickness swelling (TS) of the CF-HDPE matrix and 10/90, 20/80 and 30/70 JF/CF-HDPE composites were monitored by completely immersing the samples in the distilled water for 6600 hours (275 days). Figures 1 and 2 show water absorption (WA) and thickness swelling (TS) of the CF-HDPE matrix and JF/CF-HDPE composites plotted as a function of time (hours), for composite compositions with different percentages of jute fibers respectively. Hydrophilic property of jute fiber is responsible for water absorption in the JF/CF-HDPE composites. Water absorption and thickness swelling of the JF/CF-HDPE composite compositions is much higher than that of the CF-HDPE matrix and increases with increasing fiber content in composite compositions. 10/90 and 20/80 JF/CF-HDPE composites show less thickness swelling and water absorption as compared to the 30/70 JF/CF- HDPE due to more amount of jute fibers in the 30/70 JF/CF-HDPE composite. Figure 1. Water absorption of the CF-HDPE and JF/CF-HDPE composites at different fiber loadings Applied Polymer Composites, Vol. 1, No. 2,

6 Anshu Anjali Singh and Sanjay Palsule Figure 2. Thickness swelling of the CF-HDPE and JF/CF-HDPE composites at different fiber loadings The maximum percentage weight gains by 10/90, 20/80 and 30/70 JF/CF- HDPE composites after immersion in distilled water at room temperature for 6600 hours were approximately, 1.2%, 2.5% and 3.2% respectively. The water uptake behavior of all JF/CF-HDPE composite compositions is linear in the beginning and then slows down, but this behavior is not exhibited by the CF-HDPE matrix. The initial rate of water absorption and the maximum water uptake behavior increases for all the JF/CF-HDPE composite compositions with increase in the fiber fraction in the composite compositions. When jute fiber content increases in the composites, the number of free OH groups on jute fiber also increases, and these OH groups form hydrogen bonds with water and thereby absorb water, and that results in weight gain by the composite. The thickness swelling of the CF-HDPE and the JF/CF-HDPE composite compositions containing different content of jute fibers is shown in the Figure 2. It has been observed that the thickness swelling of the JF/CF-HDPE composite compositions increases with immersion time, reaching certain saturation value after which no more thickness swelling is observed. The thickness swelling was highest for 30/70 JF/CF-HDPE composite composition that also absorbs the highest amount of water. The maximum thickness swelling of 10/90, 20/80 and 30/70 JF/CF-HDPE composites after 200 days were approximately 2%, 118 Applied Polymer Composites, Vol. 1, No. 2, 2013

7 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process 2.4% and 2.8% respectively. The increase in the thickness swelling with increasing jute fiber content in composite compositions is due to the increased number of micro voids caused by the decrease in fiber/matrix interfacial bonding between the hydrophilic jute fiber and the CF-HDPE matrix. The thickness swelling of the CF-HDPE matrix increased for about 50 days when the maximum thickness increase was recorded as 0.70%; and after that no significant increase in thickness of CF-HDPE was observed. Effect of Water Absorption on Tensile Properties of JF/CF-HDPE Composite Tables 1 and 2 represent the tensile modulus and tensile strength for both dry and wet (water immersed for 6600 hours) samples of CF-HDPE and 10/90, 20/80 and 30/70 JF/CF-HDPE composites respectively. Tensile modulus and tensile strength of wet (water immersed) samples of CF-HDPE matrix and 10/90, 20/80 and 30/70 JF/CF-HDPE were found to be lesser than those of their respective dry samples. Studies on tensile modulus of wet CF-HDPE and wet JF/CF-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 10/90, 20/80 and 30/70 JF/CF-HDPE composites decreases by 5%, 8.5% and 22% respectively, as compared to that of the dry Table 1. Tensile Modulus of dry and wet sample of CF-HDPE matrix and JF/CF-HDPE composite Sample Tensile Modulus (GPa) (Dry) Tensile Modulus (GPa) (Wet) CF-HDPE /90 JF/CF-HDPE /80 JF/CF-HDPE /70 JF/CF-HDPE Table 2. Tensile Strength of dry and wet sample of CF-HDPE matrix and JF/CF-HDPE composite Sample Tensile Strength (MPa) (Dry) Tensile Strength (MPa) (Wet) CF-HDPE /90 JF/CF-HDPE /80 JF/CF-HDPE /70 JF/CF-HDPE Applied Polymer Composites, Vol. 1, No. 2,

8 Anshu Anjali Singh and Sanjay Palsule sample of the same composite composition. However, in absolute terms, the tensile modulus of the wet 10/90, 20/80 and 30/70 JF/CF-HDPE composites were 0.59 GPa, 0.70 GPa and 0.77 GPa respectively that are lower than tensile modulus of 0.62 GPa, 0.76 GPa and 0.94 GPa of dry sample of 10/90, 20/80 and 30/70 JF/HDPE composites respectively. Similarly the studies on tensile strength of wet CF-HDPE and wet JF/CF- 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 10/90, 20/80 and 30/70 JF/CF-HDPE composites decreases by 5%, 6% and 9% respectively, as compared to that of the dry sample of the same composite composition. However, in absolute terms, the tensile strength of the wet 10/90, 20/80 and 30/70 JF/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 JF/ HDPE composites respectively. This study shows that the tensile properties of the JF/CF-HDPE composites are adversely affected by moisture absorption and water uptake because water adversely affects the fiber/matrix interfacial adhesion in the composite. Natural 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. Figure 3. Water absorption in JF/CF-HDPE composite and its effect on fiber/matrix interface 120 Applied Polymer Composites, Vol. 1, No. 2, 2013

9 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process In case of JF/CF-HDPE composites some more reasons appear to influence the adverse effects of water on properties of the composites. Jute fibers swell due to water absorption and possibly create micro cracks in the CF-HDPE matrix (Figure 3). The matrix is also adversely affected by water uptake by processes such as chain reorientation and shrinkage [6]. The cracks, and damage due to cracks in the CF-HDPE matrix, promote capillary transport of water involving the flow of water molecules along fiber/matrix interface. Water attacks the interface, possibly de-bonding the fiber/matrix interface. As discussed above, the JF/CF-HDPE composites absorb water when immersed in water for long duration, and the -OH groups of jute fiber form hydrogen bonds with water (Figure 4). As shown in Figure 5, maleic anhydride undergoes hydration reaction and forms maleic acid [Figure 5 (I)], through a reversible reaction. Maleic acid forms hydrogen bonds either with water molecules present inside the composite [Figure 5 (II)] or with the cellulosic components Figure 4. Formation of hydrogen bonds between cellulose and water molecules Figure 5. Schematic representation of reaction in the interface of JF/CF-HDPE composite in the presence of water Applied Polymer Composites, Vol. 1, No. 2,

10 Anshu Anjali Singh and Sanjay Palsule of the jute fiber [Figure 5 (III)]. As a result, lesser ester bonds are formed between the anhydride group of CF-HDPE matrix and hydroxyl group of jute fibers because of the presence of moisture and consequently the strength and modulus of the composite decreases. This results in poor interfacial bonding between the fiber and the matrix, prevents stress transfer from the matrix to the fiber, decreases the mechanical properties of the composite, and also leads to poor dimensional stability and dimensional variation of composites. Conclusions Jute fiber (JF) reinforced chemically functionalized high density polyethylene (CF-HDPE) composites of 10/90, 20/80 and 30/70 JF/CF-HDPE compositions developed by Palsule process of using modified matrix were absorb significant amount of water when immersed in distilled water at room temperature for a long duration of 6600 hours. Water absorption and thickness swelling of the composite compositions is higher than that of the CF-HDPE matrix and increases with increasing fiber content in JF/CF-HDPE composite compositions. Tensile modulus and tensile strength of the wet JF/CF-HDPE composite compositions was lower than that of the dry JF/CF-HDPE composite compositions. Voids and capillary facilitate water transport and hydrogen bonds between Jute fibers, CFHDPE matrix and absorbed moisture promote water absorption in JF/CF-HDPE composites that adversely affects fiber/matrix interface, stress and load transfer from matrix to fiber, tensile mechanical properties and dimensional stability of the composites. References 1. Bledzki A.K. and Gassan J., Progress in Polymer Science, 24 (1999) Mohanty A.K., Misra M., and Drzal L.T., Journal of Polymers and the Environment, 10(1/2) (2002) Mohanty A.K. and Misra M., Polymer-Plastics Technology and Engineering, 34(5) (1995) Rana A.K. and Jayachandran K., Molecular Crystals and Liquid Crystals, 353 (2000) Karmaker A.C., Journal of Material Science Letter, 16 (1997) Espert A., Vilaplana F., and Karlsson S., Composites Part A, 35 (2004) Yang H.-S., Kim H.-J., Park H.-J., Lee B.-J., and Hwang T.-S., Composite Structures, 72 (2006) Applied Polymer Composites, Vol. 1, No. 2, 2013

11 Effect of Water Absorption on Interface and Tensile Properties of Jute Fiber Reinforced Modified Polyethylene Composites Developed by Palsule Process 8. Dhakal H.N., Zhang Z.Y., and Richardson M.O.W., Composites Science and Technology, 67(7-8) (2007) Shakeri A. and Ghasemian A., Applied Composite Materials, 17 (2010) Girisha. C., Sanjeevamurthy, and Srinivas G.R., International Journal of Engineering and Innovative Technology, 2(3) (2012) Azwa Z.N., Yousif B.F., Manalo A.C., and Karunasena W., Materials and Design, 47 (2013) Palsule S., Proc International Conference on Natural Polymers their Composites, (ICNP), 42, IMSE, Kottayam, India Priyanka, Palsule S., Composite Interface, Accepted (2013) doi: / Palsule S., Ogusile B.O., Priyanka, and Singh A.A., Applied Polymer Composites, 1(1) (2013) Singh A.A. and Palsule S., Composite Interface, Submitted, (2013). Applied Polymer Composites, Vol. 1, No. 2,

12 Anshu Anjali Singh and Sanjay Palsule 124 Applied Polymer Composites, Vol. 1, No. 2, 2013