NATURAL FIBER REINFORCED FUNCTIONALIZED STYRENIC POLYMER COMPOSITE

Abstract

Renewable, eco-friendly, biodegradable, and sustainable natural fibers offer good properties and are replacing synthetic and inorganic fibers, as reinforcements for polymer composites. Eco-friendly natural fiber reinforced polymer composites have good properties and therefore offer several commercial and industrial applications and support agro-based economy. Due to the presence of hydroxyl groups in their constituents, natural fibers are polar and hydrophilic and polymers are non-polar and hydrophobic, and this creates a poor interfacial adhesion between them and that limits the mechanical properties of a natural fiber/polymer composite. Following three processes are used to improve the fiber/matrix interfacial adhesion in natural fiber/polymer composites: (i) Fiber treatment process (ii) Compatibilizer process (iii) Palsule process. Their combinations are also used: (iv) Combined Fiber Treatment and Compatibilizer Process (v) Combined Fiber Treatment and Palsule process. Matrix polymers for the composites by Palsule process have been functionalized by maleic anhydride (MA) and by glycidyl-methacrylate (GMA). The MA functional groups of the polymer react with the –OH groups of the reinforcing natural fiber and develop adhesion between them in the composites by Palsule process by developing ester and hydrogen bonds. In the case of GMA functionalized matrix, the GMA functional groups of the polymer react with the –OH groups of the reinforcing natural fiber and develop interfacial adhesion in the composites by developing ether bonds and hydrogen bonds. Natural fiber reinforced composites have been developed by the Palsule process that are based on a MA functionalized graft or block copolymer as the matrix, which has a relatively small content (up to 10%) of the MA functional group and the composites have been processed up to 150oC, except the two composites that have been processed at relatively higher temperatures, around 190oC, retaining the stability of thermally sensitive natural fibers. This study extends the Palsule process to natural fiber reinforced MA chemically functionalized polymer composites, based on a MA functionalized matrix polymer requiring processing at higher temperatures, (relative to the reported composites by Palsule process) retaining the thermal stability of the thermally sensitive natural fibers, and also evaluates their recycling. Accordingly, this study, selects a newer polymer, that is functionalized, not as graft nor as block co polymer, but as a random copolymer, and also contains higher amounts (18%) of functional groups. Given the success of the styrenic CF-SEBS, CF-ABS and CF-SAN matrix composites by the Palsule process, this study evaluates a styrenic polymer as the matrix, a polystyrene polymer functionalized with 18% maleic anhydride (MA), a chemically functionalized polystyrene (CF-PS), as the matrix, that requires relatively higher processing temperature (up to 210℃). This study selects two original untreated natural fibers as reinforcement, Bagasse fibers (BGSEF) and Sisal fibers (SLF), as reinforcements. Thus, this study develops two composites, BGSEF/CF-PS composites and SLF/CF PS composites, evaluates their structure and properties, and also recycles them, to examine the reinforcement / matrix adhesion in the recycled composites and recycling effects on the properties of the recycled composites. The BGSEF/CF-PS and SLF/CF-PS Composites were processed with twin screw extrusion and injection moulding to obtain their ASTM standard specimens. Both, the BGSEF/CF-PS and SLF/CF PS composites showed higher tensile and flexural properties, but lower unnotched Izod impact strength than their respective matrix. The SEM micrographs show reinforcement embedded and covered with matrix, with a possibility of reinforcing fibre breakage, but no fibre pull out and no voids. FTIR spectroscopy of the composites, establishes this good fiber/matrix adhesion in the BGSEF/CF-PS composites and SLF/CF-PS composites, as resulting from the esterification reaction and the hydrogen bonding between the hydroxyl groups of the natural fibers and the maleic anhydride group of the chemically functionalized CF-PS polymer matrix, as per the Palsule process. Both the composites, the BGSEF/CF-PS composites and SLF/CF-PS composites have thermal stability in-between their respective reinforcing natural fiber and the matrix and are thermally stable at-least upto 290oC. The water absorption percentage and thickness swelling of the BGSEF/CF-PS composites and SLF/CF-PS composites increased with the increase in the amount of reinforcement in them. The water absorbed wet composites show lower tensile and flexural properties with reference to the dry composites, but higher than that of the dry CF-PS matrix. The BGSEF/CF-PS and the SLF/CF-PS composites have several potential applications in commodity, commercial and also light engineering systems. The R-(BGSEF/CF-PS) and R-(SLF/CF-PS) Composites have been obtained by the first recycling of the original BGSEF/CF-PS and the original SLF/CF-PS composites respectively and processed with twin screw extrusion followed by their injection molding for their ASTM standard samples. Both the composites, (R-(BGSEF/CF-PS) and R-(SLF/CF-PS), show higher tensile and flexural properties, but lower unnotched Izod impact strength relative to the recycled matrix. The SEM micrographs show that the reinforcement has remained embedded in and covered with matrix, even after recycling, establishing the retention of good adhesion between the matrix and the reinforcement in the recycled composites, and the FTIR spectroscopy establishes this retention due to the esterification reaction and the hydrogen bonding between the hydroxyl groups of the reinforcement and the matrix, (as in the original composites), as per the Palsule process. Both the composites, the R-(BGSEF/CF-PS) and R-(SLF/CF-PS) composites are thermally stable at-least upto 269oC. The R (BGSEF/CF-PS) composites and the R-(SLF/CF-PS) composites have the potential to replace the respective original composites (with lower reinforcement (BGSEF/SLF) contents and similar properties) for the respective commodity, commercial and also light engineering systems. Of all the composites (the two original and the two recycled composites), the highest tensile strength and tensile modulus, is exhibited by the 30/70 SLF/CF-PS composite, however, the lowest tensile elongation at break is exhibited by the 30/70 R-(BGSEF/CF-PS) composite and the highest flexural modulus and strength is exhibited by the 30/70 SLF/CF-PS composite. The highest unnotched Izod impact strength is demonstrated by the 30/70 BGSEF/CF-PS composite. The 30/70 SLF/CF-PS composite shows the highest thermal stability up to a temperature of approx. 305°C.