NATURAL FIBER REINFORCED FUNCTIONALIZED STYRENE ACRYLONITRILE COMPOSITES

Abstract

Recent work is directed towards significant advancements in the applications of renewable, eco friendly, biodegradable, and sustainable natural fibers as reinforcements for polymer composites. Due to their excellent properties, these natural fibers are replacing synthetic and inorganic fibers as reinforcements for several polymer composites. Natural fibers reinforced polymer composites have many commodity, commercial, and engineering applications, and these composites promote agro-based agricultural economy and support farmers cultivating these natural fibers. However, the inherent polarity and hydrophilicity of natural fibers, due to the presence of hydroxyl groups in their ligno-cellulosics, in contrast with the non-polar and hydrophobic nature of polymers results in their poor interfacial adhesion, limiting the mechanical performance of these natural fiber/polymer composites. Following three processes and their combinations have been developed to enhance the fiber/matrix interfacial adhesion in natural fiber/polymer composites, as follows: (i) Fiber Treatment Process, for the reinforcement (ii) Compatibilizer Process to improve the reinforcement/matrix interface and (iii) Palsule process, wherein the used matrix is a functionalized polymer. Their combinations are also being used: (iv) Combined Fiber Treatment and Compatibilizer Process, and (v) Combined Fiber Treatment and Palsule Process. In Palsule process, the functional groups of a chemically functionalized polymer matrix react with functional groups of lingo-cellulosic of a natural fiber and impart improved interfacial adhesion between the reinforcing natural fiber and the functionalized polymer matrix. The process does not need any fiber treatment and also does not need any compatibilizer, for processing the natural fiber/polymer composite. Composites based on following functionalized polymers have been reported by Palsule process: functionalized polyolefin (CF-PE and CF-PP) based composites; functionalized thermoplastic elastomer (CF-EPR and CF-SEBS) based composites: functionalized thermoplastic (CF-ABS) based composites. All these composites are based on matrix polymers functionalized by maleic anhydride (MA). In these composites, fiber/matrix adhesion results from esterification and hydrogen bonding between them. Palsule process has been extended to composites based on matrix polymers functionalized by glycidyl methacrylate (GMA) and GMA functionalized CF-VLDPE and CF- EBA composites have been reported. In these composites, fiber/matrix adhesion results from etherification and hydrogen bonding between them. iii Reported natural fiber-reinforced composites developed by the Palsule process are based on polymer matrix functionalized by grafting, but containing a relatively low concentration (up to 3%) of the MA / GMA functional groups. These composites have been processed at temperatures up to 150°C, with the exception of CF-ABS composites processed at higher temperatures around 190°C, while still maintaining the stability of thermally sensitive natural fibers. This study extends Palsule process to a matrix polymer, functionalized by a method, other than grafting, and having higher (approx. 10%) functionality; and requiring higher (195oC) processing temperature and processing by extrusion at more than 350 rpm of the twin screws of the extruder. In view of success of styrenic polymers based natural fibers reinforced composites by Palsule process; this study selects a styrenic polymer, a chemically functionalized styrene-acrylonitrile polymer (CF-SAN), as the matrix. This CF-SAN is a random ter-polymer (not graft) with higher functionality (approx. 10%), and requires processing at a temperature of 195oC. This study selects two reinforcing natural fibers, untreated kenaf fibers (KNF) fibers and untreated hemp fibers (HMPF) that have approx. 10% difference between their holo-cellulose and also lignin contents. This study develops two composites: KNF/CF-SAN composites and HMPF/CF-SAN composites and evaluates their structure and properties. This study also performs only one, the first recycling of these composites, to assess the impact of recycling on the reinforcement/matrix adhesion in the recycled composites, and its effects on the properties of the composites. Following properties of the composites are evaluated: Mechanical: tensile, flexural and impact properties; dynamic mechanical thermal: tan-, storage modulus and loss modulus properties and thermal properties: initiation of degradation temperature, temperature at the maximum rate of degradation and residual mass at 800oC. The KNF/CF-SAN and HMPF/CF-SAN composites have been processed by twin-screw extruder, operated at more than 350 rpm, and their ASTM standard samples have been processed by injection molding process. FE-SEM micrographs reveal reinforcing fibers embedded in and coated with the matrix, with potential fiber breakage observed, though no fiber pull-out or voids were detected. ATR-IR spectroscopy confirmed fiber/matrix adhesion in both composites, attributed to the esterification reaction and hydrogen bonding between the hydroxyl groups of the natural fibers and the maleic anhydride groups in the chemically functionalized CF-SAN iv polymer matrix, in accordance with the Palsule process. Tensile and flexural modulus and strengths, and unnotched Izod impact strength of both, KNF/CF-SAN and HMPF/CF-SAN, composites are higher than that of their respective CF-SAN matrix and increase with the increasing amounts of reinforcing KNF and HMPF, in the composites; however, their tensile elongation at break is lower than that of their respective CF-SAN matrix and decreases with increasing amounts of reinforcing fibers, KNF and HMPF in them. The measured tensile strength and tensile modulus values of KNF/CF-SAN and HMPF/CF-SAN composites developed in this study have been compared with the values predicted by various equations. Dynamic mechanical thermal properties (storage modulus and loss modulus) of both, KNF/CF-SAN and HMPF/CF SAN, composites are higher than that of their respective CF-SAN matrix and increase with the increasing amounts of reinforcing KNF and HMPF, in the composites. Thermal analysis indicates that the thermal stability of both, KNF/CF-SAN and HMPF/CF-SAN, composites is intermediate between that of the reinforcing KNF and HMPF and the CF-SAN matrix. Both composites, KNF/CF-SAN and HMPF/CF-SAN, are environmentally friendly and provide both technological and economic benefits. They also offer various potential applications.