Biodegradation of Treated Polylactic Acid (PLA) under Anaerobic Conditions

Abstract

Biodegradation of untreated and treated thermoformed polymer polylactic acid (PLA) under anaerobic conditions was investigated. Treatments consisted of subjecting PLA to irradiation (gamma source and e-beam) and steam (120°C for 3 h). Absorbed doses were 72 and 172 kGy for gamma-irradiated samples and 72, 144, and 216 kGy for e-beam irradiated samples. Methods to assess biodegradation were weight loss of irradiated PLA and biochemical methane potential (BMP) of steam-treated PLA during anaerobic digestion at mesophilic (37°C) and thermophilic (58°C) conditions. Untreated PLA degraded only at thermophilic conditions. Treated PLA degraded at both conditions and was more sensitive to biodegradation, showing greater weight loss and methane yield. The order of effectiveness of treatments from greatest to lowest was steam exposure, gamma irradiation, and e-beam irradiation. Under thermophilic conditions, gamma-irradiated PLA lost 45% of its weight in 180 days, and steam-treated PLA produced methane at 225 cc CH4 per gram in 56 days. The most significant finding of this work is that PLA degrades under anaerobic thermophilic conditions, suggesting that post-consumer PLA material may be used in anaerobic digestion for energy recovery, instead of being treated as waste disposal.