Polyhydroxyalkanoate (PHA) bioplastics from organic waste

Polyhydroxyalkanoates (PHA) bioplastics, which are produced by pure and mixed culture biotechnology, are high-performance and truly biodegradable materials. The use of organic wastes as feedstocks for PHA production has been widely documented, though the focus has been on increasing PHA yield; knowledge of the resulting polymer quality and processability has been lacking. In this chapter, it is shown that copolymer composition, blend composition, thermal properties, molecular weight, type of processing and other characteristics such as microstructure and crystallisation kinetics all govern the mechanical properties, but property-structure relationships are complex, and therefore more research in this space is needed, regardless of the feedstock. Still, there is no doubt that organic wastes can be used as feedstocks for PHA production—particularly if they are pretreated—and there is now interest in commercialisation of PHA bioplastics from such wastes. But further advances are tempered with the conclusion that, for organic wastes to be viable feedstocks, the waste must be relatively abundant, concentrated and readily degradable. For some perspective, mass flows of organic wastewater streams from some relevant Australian industries are presented. It is shown that only if all the wastes from any given industry were collected and consolidated would there be sufficient feedstock for production of industrially relevant volumes of PHA