| Wood/Natural fiber plastic composites (W/NPCs) have been widely accepted and are an enormously growing segment of the commodity plastics market. These are predominantly being used in decking, household interiors, etc., and more recently have made inroads in automotive interior applications. These are short fiber composites developed by using wood/natural fiber as reinforcement in the plastic matrix. Generally, plastic constitutes from 30 to 70% of the entire product mass of the composite and the most used plastics are conventional petroleum based i.e., polyethylene, polyvinyl chloride, polypropylene and nylon. Polyhydroxyalkanoates (PHAs) are bacterially produced plastics from commonly available biomass, and are projected to be sustainable and viable alternatives to petroleum based plastics. This research focuses on a holistic approach to shift W/NPCs from partially to fully green biocomposites, by replacing the conventional plastic constituent in the W/NPCs with a renewable source based and biodegradable bioplastic i.e., PHAs. This broadly addresses the evolving environmental concerns related to conventional petro-plastics. In this process of transformation from partially to fully green bio-composites, issues coupled to biopolymers based W/NPCs such as, cost, processablity, performance, compatibility of reinforcing agent and matrix, and raw material availability are addressed. These fully green biocomposites can find potential applications in rigid packaging, distribution, household items and automotive interiors.This dissertation advances in four consecutive syllogistic stages: (1) In the first stage, the development of wood fiber reinforced bio-plastic i.e., polyhydroxybutyrate-co-valerate (PHBV) bio-composites is accomplished on the performance evaluation, and comparison to conventional WPCs is addressed. (2) In the second stage, bio-composites from natural fiber, i.e., bamboo fiber, and PHBV, at 30 & 40 wt% fiber content, were fabricated and their analogy to wood fiber reinforced PHBV bio-composites is determined. (3) In the third stage, a comparative study of anisotropy, static and dynamic mechanical evaluation of biocomposites fabricated using two different molding processes, i.e. injection and compression molding, was accomplished. (4) In the final stage, "green hybrid bioplastic composites" containing synergistic reinforcements of talc and wood fiber were designed and fabricated.The biocomposites were extrusion processed followed by injection molding and analyzed for static and dynamic mechanical, thermal & morphological aspects. The tensile and flexural modulus of the bio-composites with 40 wt% of the wood fiber was enhanced by ~167%, and the heat deflection temperature by 21%. Statistically, there was no effect of the fiber type (i.e., bamboo and wood fiber) on the mechanical properties, except for notch impact strength and heat deflection temperature. The squeeze flow test revealed the anisotropy in the injection molded short fiber bio-composites. Synergetic reinforcement of the talc platelets and cylindrical wood fibers increased Young's and flexural modulus, by ~200%, at 20 wt% of each in PHBV. The high surface energy of talc platelets allows good talc-PHBV interfacial interactions as shown by the morphological study and no additional crystallization of PHBV was observed. |
