Chemical Recycling of Polyester Wastes: Emerging Upcycling Technologies, Fundamental Mechanisms, Process Analysis, and Machine Learning

With annual production exceeding 100 million tons, the disparity between the scale of polyester manufacturing and current waste management capabilities presents a challenge to the global circular economy. Chemical recycling, capable of depolymerizing polyester waste into monomers or upcycling it into value-added products, is a strategy for achieving a potentially sustainable, closed-loop polyester economy. This review synthesizes recent advancements in the field and establishes a framework for future research. The molecular-level influence of polyester chemical structures on depolymerization pathways and efficiency is elucidated. Building upon these insights, the review critically examines progress in the recycling of polyethylene terephthalate and polylactic acid, providing an in-depth analysis of the transition from traditional solvolytic depolymerization to emerging approaches, such as photocatalytic and electrocatalytic upcycling. The conversion of mixed polyesters and the resilience of processes with complex feedstock impurities are further discussed. Furthermore, this review integrates analyses of recent industrial cases, techno-economic analysis, and life cycle assessment, while highlighting the potential of artificial intelligence in catalysis and process optimization. Finally, it critically identifies key barriers related to reaction efficiency, stability, and economic feasibility, offering a forward-looking perspective on future developments in the field.