Anaerobic biodegradation under slurry thermophilic conditions of poly(lactic acid)/starch blend compatibilized by maleic anhydride

Abstract

TPS/MA/PLA is a blend of thermoplastic starch (TPS) and polylactic acid (PLA) compatibilized by maleic anhydride (MA) that can be a substitute for petro-based plastics in certain applications. At the end of its life, this material must be properly disposed in treatment systems such as composting or anaerobic digestion. The biodegradability of TPS/MA/PLA, PLA, TPS and the non-compatible mixture (TPS/PLA) was evaluated in a slurry thermophilic anaerobic digestion system (STAD) according to ISO 13975-2012 standard. The anaerobic inoculum was prepared from cow manure and the organic fraction of municipal solid waste. After 31 days of incubation, the pure PLA exhibited a 12-day lag phase and 40.41% of biodegradability. TPS, TPS/PLA and TPS/MA/PLA did not exhibit lag phase and reached 92.11%, 65.48% and 64.82% of biodegradation respectively. The slow degradation rate of PLA is attributed to its high glass transition temperature and crystallinity. In TPS/MA/PLA and TPS/PLA, about 50% of PLA and 13% to 10% of the TPS remains undegraded and MA did not affect the biodegradation of TPS/MA/PLA compared to TPS/PLA. Results suggest that, in very short retention times STAD systems, PLA based materials could not exhibit enough biodegradability.