Recycling of Poly(lactic acid): From Molecular Degradation to Circular End-of-Life Strategies

Poly(lactic acid) (PLA) is widely recognized as a biodegradable bioplastic, yet reliance on industrial composting alone can forfeit embedded material and energy value when recovery is technically feasible. Recycling can retain this value, but PLA performance is affected by service-life aging, hydrolytic cleavage, thermal and shear history, and contamination. Whereas previous literature often treats end-of-life routes separately, this review integrates mechanical reprocessing, reactive upgrading, chemical and hydrothermal depolymerization, and life-cycle assessment within a feedstock–process–structure–performance–safety–circularity framework. We examine how molar mass, rheology, crystallinity, and mechanical performance evolve during recycling, and compare upgrading strategies, including chain extenders, plasticizers, blends, and fillers, in terms of property restoration, recyclability, migration, and ecotoxicity trade-offs. Chemical and hydrothermal routes are evaluated according to monomer yield, stereochemical purity, additive tolerance, repolymerization potential, and process severity. Life-cycle evidence shows that circularity cannot be defined solely by climate impact or biodegradability, as burden shifting may occur in terms of toxicity, energy demand, land use, and resource consumption. Accordingly, we propose a decision map linking feedstock quality with suitable routes and target applications. Overall, clean, dry, and traceable PLA should be prioritized for mechanical recycling, whereas degraded or contaminated streams require evidence-based upgrading or depolymerization instead of default disposal or composting practices.