Solvent and Catalyst-Free Depolymerization of Polylactic Acid Waste to Lactide Enabled by Dry Steam

The growing promise of biodegradable polymers, notably polylactic acid (PLA), as alternatives to petroleum-based nonrenewable plastic, is emphasized by their ecologically friendly characteristics. However, natural degradation of PLA produces CO2 and wastes renewable carbon resources. Herein, we demonstrate a dry steam method, enabling direct depolymerization of PLA to lactides (LT) in the absence of additional solvents or catalysts, which achieved a 43.4% yield of LT at 190 °C. It has been revealed that disconnected PLA fragments undergo a recrystallization process in the dry steam environment, which prevents the thorough depolymerization of PLA to lactic acids. The carbon footprint associated with LT derived from PLA waste via the dry steam method (0.07 CO2 eq/kg LT) is markedly reduced compared to conventional industrial LT production (1.02 CO2 eq/kg LT). This study presents a novel eco-friendly route to recycle PLA waste and offers a new strategy for polyester plastic depolymerization.