Pretreatment technologies to enhance enzymatic biodegradation of polyurethanes

Polyurethanes represent one of the most widely produced synthetic polymers, with applications in construction, automotive, consumer goods, and biomedical sectors. Their extensive use, combined with high durability, complex formulations, and insufficient end-of-life management, has resulted in significant environmental accumulation and recycling challenges. Conventional disposal routes are associated with slow degradation rates and the release of hazardous byproducts, while chemical recycling methods are often constrained by high energy demands and limited economic viability. Enzymatic biodegradation has emerged as a sustainable alternative due to its lower energy requirements and reduced environmental impact. However, resistance of polyurethanes to biological attack, arising from their segmented structure, high crystallinity, cross-linked networks, and widespread use of additives, limits enzymatic efficiency. To date, most reported polyurethane-degrading enzymes exhibit esterolytic activity and are primarily effective against polyester-based polyurethanes, while efficient enzymatic cleavage of urethane bonds, particularly in polyether-based systems, remains limited. Recent studies indicate that pretreatment strategies can enhance polyurethane susceptibility to enzymatic degradation, although systematic evaluation remains limited. To address the limitations of standalone recycling methods, this review provides a systematic, comparative analysis of pretreatment technologies aimed at breaking down complex polyurethane networks to enhance enzymatic degradation. We examine how different pretreatments alter polyurethane structure and improve enzymatic accessibility, and identify key challenges, knowledge gaps, and future research directions. Pretreatment is therefore needed for efficient enzymatic polyurethane recycling, and chemical depolymerization combined with enzymatic hydrolysis is currently the most effective approach.