Impact of temperature and soil type on biopolymer and bioplastic degradation

The aim of this project was to understand how the degradation of biopolymers used as an alternative to plastic varied across different soil environments and temperatures. An 8-month laboratory degradation experiment tested a traditional non-degradable polymer (Polypropylene) and biopolymers (Polyhydroxybutyrate, Polycaprolactone, compostable bags, tea, cotton), in three soil types (urban, rural and compost) at 4°C, 12°C and 20°C. A meta-analysis was also conducted on studies that investigated the degradation of polyhydroxyalkanoates in different soil environments and the impact of the different environmental variables influencing their degradation. The effect of temperature in the lab experiment showed that at higher temperatures degradation occurred more rapidly across the biopolymers. In compost there was a positive correlation showing that as temperature increased so did the degradation rates of PHAs. Degradation environment was shown to be significant in the lab experiment with the most degradation occurring in compost derived soil and the least degradation occurring in the urban soil. Environment type was significant in influencing the total degradation and the rate of degradation for the biopolymers. The order for most degradation to least was PHB > PCL > Polycomp > PLA > PP. In the meta-analysis there was a significant difference across environment types in total degradation and rate of degradation, with the most degradation occurring in the order of anaerobic digestion followed by compost, soil and the least in activated sludge. No significant differences were found between time to reach 25% and 50% across the different environments as well as no significant differences in monomer and copolymer degradation of PHAs across the different environments. Overall, this study showed the range in degradation potential for biopolymers and PHAs specifically in different environments and across temperatures. This work is relevant in helping to build suitable policies to manage the proper disposal of biopolymers.