Volume 38, Issue 6 (November 2010)
Industrial Composting of Poly(Lactic Acid) Bottles
In order to better understand the end of life scenario potential of poly(lactic acid) (PLA) packaging to reduce waste through composting when properly disposed, this study aimed to determine the rate at which 473 mL (16 oz) PLA bottles with and without associated high density polyethylene (HDPE) caps and polypropylene (PP) labels decomposed in an industrial compost pile. Temperature, moisture content, and pH levels of the compost pile were recorded throughout the study to determine their effects on the rate of decomposition and to ensure optimal conditions were met. Analyses performed at weeks 2, 4, and 8 showed that from week 2, a 94 % reduction of mass and weight average molecular weight occurred, along with a complete loss of structural integrity. PLA bottles without caps and labels were considered to be decomposed completely by week 4, while the bottles with the HDPE caps and PP labels showed plastic residues until week 8. The caps and labels acted as a barrier that slowed the rate of biodegradation. This study showed that PLA bottles can be composted in industrial composting facilities in 30–45 days, and it is recommended to remove all caps and labels. The results further indicated that if a proper infrastructure is put in place to allow large scale composting of PLA, this packaging polymer could have a significant impact on reducing municipal solid waste.