Purification and Modification of Poly (β-hydroxybutyrate) for Food Packaging and Biomedicine Applications

Abstract

Due to growing concern over the environmental impact of the global polymer industry, there is increasing interest in sustainable alternatives. Poly (β-hydroxybutyrate) (PHB) is posed as a viable renewable and biodegradable alternative to conventional polyolefins, particularly for food packaging and biomedical applications. However, PHB has limitations in that it is extremely brittle, hydrophobic and contains trace amounts of undesirable embedded impurities. Addressing these limitations is necessary to enable the commercial application of PHB and is the focus of this thesis. High pressure CO2 technologies, can effectively remove up to 93 ± 3 wt% of these embedded residues, this purification process makes PHB suitable for use in food packaging and for biomedicine. A novel tri-blend of PHB with Polypropylene Carbonate (PPC) and a PHB-based modifier can achieve comparable tensile strength (up to 17 MPa), rigidity (up to 320 MPa) and elasticity (up to 240%) to conventional polyolefins currently used for food packaging. The performance of the novel blend was further evaluated by the fabrication of effective orthopaedic screws. Similarly, the inclusion of a PHB-based crosslinking agent in a conventional hydrogel provided 4-17 fold superior strength per strain performance over the other commercially available cross-linkers examined, such as poly (ethylene glycol) diacrylate (PEGDA) and methacryl-polyhedral oligomeric silsesquioxane. These PHB-based hydrogels were found also to have superior rigidity (0.95-18 MPa) and comparable strength (580-1750 kPa) to some toughened hydrogel systems. The simplified fabrication method of these PHB hydrogels can be easily utilised in advanced processing technologies, such as 3D printing. The three technically feasible solutions proposed in this dissertation overcome the limitations to the further utilisation of PHB within the food packaging and biomedical markets leading PHB to become the biopolymer of the 21st century.