Degradability of biodegradable plastic under controlled composting conditions

Biodegradability of poly(ß-propiolactone) (PPL), one of biodegradable plastics, was tested in a bench-scale composting reactor under controlled conditions, with uniform temperature, moisture content, and aerobiosis maintained. The composting raw mixture was prepared by mixing commercial dog food instead of real organic waste, saw dust as a bulking agent, commercial inoculum sold for acceleration of composting, and PPL in the ratio of 10:9:1:10 on dry weight basis. The degree and rate of PPL degradation were determined by comparing the difference in the CO₂ evolution for composting with and without addition of PPL. The influence of temperature on the degradability of PPL was investigated at 40, 50, and 60 °C and the optimum temperature was found to be around 40-50°C where ca. 40 wt.-% of PPL was decomposed in 8 days. The effect of inoculum on the degradability of PPL during 50 °C composting was then examined, a considerable difference (100%) being observed in the biodegradability using two different inocula.