Process Integration and Life-Cycle Assessment of Moist-Solid Hydrolysis of Polylactic Acid with Lactic Acid Recovery...

Poly(lactic acid) (PLA), a biodegradable plastic derived from starch, has gained prominence as a sustainable alternative to petroleum-based plastics. However, the slow degradation of PLA in natural environments and contamination of recycling streams due to incompatibility with other plastics highlight the need for efficient recycling techniques. This study reports a sustainable closed-loop PLA recycling strategy by hydrolysis depolymerization under moist-solid condition and recovery of the valuable monomer lactic acid. By employing ball milling and resonance acoustic mixing, the effects of milling speed, time, ball size, alkali type, and ageing on lactate yield are investigated, to optimize the performance and the efficiency of mechanical and moist-solid conditions in polymer chain scission without bulk heating is demonstrated. Furthermore, a bipolar membrane electrodialysis process for conversion of lactate to lactic acid is integrated with simultaneous NaOH production, enhancing the sustainability of the recycling process. Life-cycle assessment (LCA) is employed to assess the environmental impact of such PLA recycling approach for lactic acid production and provide recommendations for future improvements. This work demonstrates the effectiveness and environmental benefits of mechanically induced moist-solid chemical recycling and integration with advanced membrane separation processes, offering a promising pathway for sustainable PLA waste management and lactic acid production.