Processing and Characterization of Sustainable Polymers: Recycling, Renewable Resources, and Reduction

This Ph.D. study aims to advance the understanding and know-how of sustainable polymers and composites to reduce their environmental impact and enhance their utilization. This can be done through recycling post-consumer plastics, using biodegradable polymers made from renewable resources, and reducing material usage in final products through foaming or stronger polymer composites. To evaluate the performance of these polymers and composites, the mechanical, thermal, rheological, morphological properties, and other relevant properties have been characterized.;The first chapter deals with recycling poly(ethylene terephthalate) (RPET), a commonly used material for beverage bottles. Melt-compounding and injection molding of RPET with various additives were performed. The addition of chain extenders greatly enhanced the moldability and mechanical properties of RPET. While the RPET and thermoplastic elastomer blends showed improved mechanical properties, the improvement was less significant and the blends were often immiscible due to the difference in polarities between the RPET and the thermoplastic elastomer.;Replacing non-biodegradable polymers with renewable/biodegradable polymers, e.g., poly(lactic acid) (PLA), was studied and reported in the second chapter. The injection molded PLA, after annealing treatment, offered several benefits such as a higher glass transition temperature, better heat resistance, and greater storage modulus and tensile strength. This study pointed to a new post-molding treatment that could enhance the heat resistance, which is one of the major weaknesses of PLA components. The degree of crystallinity after long annealing times resembled those observed at higher temperatures, suggesting a time-temperature super position relationship.;The study reported in chapters three and four reduced material usage by developing polymer composites or employing foaming. Nanofibrillated cellulose (NFC) from newable resources was used as a filler in both hydrophilic polymer polyvinyl alcohol (PVOH), and hydrophobic polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate, PHBV). An NFC fiber suspension was stirred with PVOH in water, followed by casting. PHBV powders were mixed with an NFC fiber suspension in water, freeze-dried, and melt compounded. NFC had a reinforcing effect and served as a nucleating agent but led to greater thermal degradation for both polymers. The addition of NFC yielded finer foamed morphologies in PVOH films but inhibited foaming in PHBV.