INVESTIGATION OF A SUSTAINABLE ALTERNATIVE - WOOD BIO-PLASTIC COMPOSITES
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Bio-polymers have become a focus for developing wood bio-plastic composites since they can be sustainably renewed from agricultural resources. One of the bio-polymers, poly-3-hydroxybutyrate (PHB), has been widely studied for its performance enhancement by blending with wood flour and coupling agents. One riddle of the influence from coupling agents on PHB/wood flour (WF) composites was discussed in this study. A lab-scale composting evaluation test was developed based on ASTM standards in order to understand the compostability of PHB/WF composites. During the compostability evaluation, multiple phases of biodegradation such as lag, biodegradation, and slow down phases were observed. Theoretically, microcracks occurred during the lag phase, which is a combination of physical (microcracks) and chemical (decomposition) degradation. The following phase of biodegradation occurs when the organic matter of PHB/WF composites rapidly converts to carbon dioxide, known as mineralization behavior in its biological definition. In addition, this carbon conversion process is involved in a carbon cycling ecosystem. Mineralization results indicated that PHB was consumed faster than wood flour. Wood flour was then believed to challenge the compostability of the PHB/WF composite. It was also observed that hypha could not reach the PHB located in the core of the composite. This phase is the slow down phase. Without coupling agents, an in accordance with ASTM standards and the results found this study, the PHB/WF composite is certified as a compostable polymeric material. Furthermore, purification of producing neat PHB has been reported as consuming more energy than producing polyolefin. By eliminating the purification step of PHB production, energy consumption could be limited and seen to reduce. In this study, the PHB/wood flour/cell debris (PWC) composites were successfully developed and produced through injection molding and extrusion processes. The mechanical performance and moisture diffusion behaviors of the PWC composites were comparable with a commercial wood plastic composite. Therefore, a sustainable alternative - wood bioplastic composite was developed by maintaining biodegradability and its carbon footprint was effectively controlled, both of which are sustainable requirements.