Comparative Assessment of Degradation Pathways for Enzymatic Degradation of Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET) and their Degradation Intermediates

Elucidating how polymer chemistry and substrate crystallinity collectively determine polyester degradability is a key to advancing enzymatic recycling as it enables predictive assessment of the degradation behavior of novel substrates and accelerates the development of efficient recycling strategies. Achieving this requires a systematic comparison across different polymer chemistries and crystallinity states. However, direct comparative studies remain scarce. Here, we compare the enzymatic degradation pathways of amorphous and semicrystalline poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) using the cutinase LCCiccg. Degradation pathways are characterized through changes in soluble degradation products, surface chemistry and morphology, surface and bulk crystallinity, semicrystalline structures, and mechanical properties. Identified degradation intermediates are synthesized and evaluated for their enzymatic and abiotic hydrolyzability and inhibitory effects on polymer degradation. Across both polymers, enzymatic hydrolysis follows the same cleavage mechanism, whereas substrate crystallinity determines the extent to which degradation can proceed and thereby governs the resulting morphological and mechanical changes. The findings further support a common desorption–readsorption mechanism linking chain accessibility to localized hydrolysis and the persistence of crystalline domains. Collectively, these results reveal two independent axes of transferability: the enzymatic cleavage mechanism is conserved across polymer chemistries, whereas the resulting morphological and mechanical responses are governed primarily by substrate crystallinity.