A Combined Thermochemical and Microbial Process for Recycling Polylactic Acid Polymer to Optically Pure l -Lactic Acid for Reuse

Polylactic acid polymer (PLA) produced from renewable resources can be recycled at the end of life to constituent monomer, optically pure lactic acid (LA), by a combination of chemical and biological processes. Efficient application of this closed loop of LA-PLA plastics-LA can minimize accumulation of plastics waste that pollute land and oceans. Temperature-dependent hydrolysis of PLA in water to LA follows apparent first order decay kinetics after a short lag. A modified Gompertz equation can explain the overall hydrolysis process. Alkali increased the rate of hydrolysis of PLA and reduced the length of lag period compared to water alone. The stoichiometry of base added to LA released was 1.0. The highest lactic acid yield was 0.95 g g −1 of PLA. d -LA in the syrup obtained after hydrolysis of PLA-plastics was removed using an engineered Escherichia coli to produce a l -LA syrup with an optical purity ≥ 99%. These results show that thermochemical hydrolysis of PLA-based plastics to LA with optimum amount of base followed by bio-based purification to l -LA is an effective method of recycling PLA-plastics for reuse.