Enzymatic plastic depolymerization: From lab promise to circular reality

Global plastic production continues to rise, yet most recycling strategies fail to deliver true circularity. Enzymatic plastic depolymerization has been widely promoted as a scalable solution. However, its real-world potential remains poorly defined. This review critically examines why many enzymatic approaches succeed in the laboratory yet break down when applied to heterogeneous post-consumer plastic waste. Evidence across polymers and processes shows that enzymatic depolymerization is fundamentally constrained by polymer chemistry rather than enzyme availability. Plastics with hydrolyzable backbones allow true depolymerization and closed-loop monomer recovery. In contrast, dominant polyolefins largely resist enzymatic attack, with reported effects limited to surface oxidation rather than verified chain scission. Many claimed advances rely on indirect measurements, pristine substrates, or abiotic pretreatments, overstating relevance to real waste streams. While enzyme engineering and artificial intelligence/machine learning (AI/ML)-guided design have significantly enhanced performance on hydrolyzable plastics, these gains frequently entail trade-offs in stability, specificity, and cost, and fail to address key limitations from solid-polymer interfaces and additives. Techno-economic studies indicate that optimized enzymatic recycling of hydrolyzable plastics could reach costs of $1.1-1.8/kg under favorable conditions. However, polyolefins require integrated pretreatment and hybrid chemo-enzymatic strategies for meaningful valorization. The review concludes with a constraint-aware 2030-2040 roadmap, positioning enzymatic recycling as a realistic but inherently limited contributor to a circular plastics economy.