Pustak_2025_FEBS.Open.Bio__

Plastic waste from fossil-derived polymers remains a major environmental challenge, driving interest in biopolymers and enzyme-enabled end-of-life strategies. This review synthesizes current understanding of how polymer structure and thermal state govern enzymatic degradability, with emphasis on semicrystalline architectures and state-dependent accessibility. Within the Keller-Flory two-phase framework, crystalline lamellae embedded in an amorphous matrix dictate water/enzyme diffusion, chain mobility, and hydrolysis kinetics. Enzymatic attack preferentially initiates in amorphous regions, producing characteristic biphasic behavior as amorphous domains erode faster than crystalline regions, leading to crystallinity enrichment and subsequent slowing of degradation. Thermal transitions further modulate this balance: near or above T(g), segmental mobility and free volume rise, accelerating hydrolysis if enzymes remain stable; above T(m), chain mobility is maximal, but enzyme stability typically limits feasibility. Processing and architecture also strongly influence outcomes: annealing increases crystallinity and slows mass loss, quenching suppresses crystallization and hastens degradation, random copolymerization disrupts packing and lowers T(m), while block copolymers often degrade selectively by domain. Recent advances expand the operational window toward rubbery or near-molten states for low-melting aliphatic polyesters (e.g., PCL, PLGA, PEG-b-PLA), leveraging thermophilic/engineered hydrolases (cutinases, PETases, lipases, carboxylesterases) with demonstrated stability at 60-90 degreesC. Emerging strategies-including enzyme thermostabilization, AI-guided design, disulfide grafting, smart encapsulation, and in-situ enzyme embedding-enable self-degradation of materials and accelerate inside-out depolymerization under mild triggers. Integrating thermal analysis with polymer morphology and enzyme engineering offers a path to programmable, circular end-of-life for biopolymers, translating fundamental structure-property-reactivity relationships into practical enzymatic recycling and reduced environmental impact.