Structural decay of poly(ethylene terephthalate) by enzymatic degradation

Synthetic polymers, such as plastics, are ubiquitous materials that are used in many applications. The sustainable use of plastics is becoming increasingly important given the emergent issues of environmental pollution by microplastics and the limited resources of petroleum on Earth. One of the key strategies for the sustainable use of plastics is recycling. Enzymatic degradation is a promising technique for recycling plastic because this process requires neither energy nor harsh solvents, such as strong alkaline solutions and organic solvents. In this study, the enzymatic degradation of poly(ethylene terephthalate) (PET), a major plastic used in daily life, was investigated, aiming to improve the efficiency of enzymatic degradation by understanding the decay of the polymeric PET structure. The structural decay of an amorphous PET film induced by a PET-hydrolyzing enzyme (PETase) was analyzed using wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), electron microscopy, and X-ray computed tomography (X-ray CT). Structural decay progressed from the surface of the film, and many nested pores (10 ^-8 ‒10 ^-5 m) were found in the later stage of degradation, reflecting the structural difference between the surface and core of the material. Information regarding the polymeric structure of the plastic under enzymatic degradation is important for improving the degradation performance of enzymes for realizing the biochemical recycling of plastics such as PET.