On the temperature dependence of enzymatic degradation of poly(ethylene terephthalate)

Abstract

Enzymatic recycling of poly(ethylene terephthalate), PET, has attracted significant attention in recent years. Temperature is a governing factor in the enzymatic degradation of PET, influencing simultaneously the catalytic activity and thermal stability of enzymes, as well as the biodegradability of PET materials from many perspectives. Here we present a detailed examination of the complex and mutual effects of temperature on the degradation of low-crystallinity PET (LC-PET, 7.6%) and high-crystallinity PET (HC-PET, 30%) microparticles using the WCCG variant of the leaf-branch compost cutinase (LCC). The degradation velocity apparently increases exponentially with increasing temperature at temperatures below 65 °C. Arrhenius plots show a sudden reduction in activation energy at temperatures higher than 40 °C, suggesting the onset of the surface glass transition of PET particles. This is more than 20 °C lower than the bulk glass transition temperature, underscoring the interfacial catalytic nature of enzymatic PET degradation. WCCG undergoes substantial conformational changes upon thermal incubation at temperatures ranging from 50 to 70 °C and exhibits enhanced activity, owing to the increased intrinsic catalytic activity and improved adsorption on PET surface. Further increasing the temperature leads to the inactivation of enzymes alongside the rapid recrystallization of amorphous PET, impeding the enzymatic degradation. These findings offer a detailed mechanistic understanding of the temperature dependence of the enzymatic degradation of PET, and may have implications for the engineering of more powerful PET hydrolases and the selection of favorable conditions for industrially-related recycling processes.