Depolymerization of Post-Consumer Polylactic Acid Products

Presented in this study is a novel recycling strategy for poly(lactic acid) (PLA) in which the depolymerization is rapidly promoted by the base-catalyzed hydrol-/alcohol-ysis of the terminal ester bonds under mild conditions. Post-consumer PLA water bottles were cut into approximately 6 x 2 mm plastic chips and heated to 50-60 degrees C in water, ethanol, or methanol as the depolymerization medium. A variety of carbonate salts and alkaline metal oxides were screened as potential catalysts. High-power ultrasound was also investigated as a means to accelerate the PLA decomposition. Both mass loss and HPLC analysis of the treated suspensions showed that the conversion of PLA to lactic acid/lactic esters was achieved with yields over 90% utilizing either ultrasonics or a hot bath. It was found that the most rapid decomposition occurred in solution of sodium hydroxide in methanol at 50 degrees C, in which maximum depolymerization was complete in 5 min. It was also seen that the degree of crystallinity affected the rate of depolymerization.