Abstract
The biocatalytic degradation of polyethylene terephthalate (PET) emerged recently as a promising alternative plastic recycling method. However, limited activity of previously known enzymes against post-consumer PET materials still prevents the application on an industrial scale. In this study, the influence of ultraviolet (UV) irradiation as a potential pretreatment method for the enzymatic degradation of PET was investigated. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and 1H solution nuclear magnetic resonance (NMR) analysis indicated a shortening of the polymer chains of UV-treated PET due to intra-chain scissions. The degradation of UV-treated PET films by a polyester hydrolase resulted in significantly lower weight losses compared to the untreated sample. We also examined site-specific and segmental chain dynamics over a time scale of sub-microseconds to seconds using centerband-only detection of exchange, rotating-frame spin-lattice relaxation (T1ρ), and dipolar chemical shift correlation experiments which revealed an overall increase in the chain rigidity of the UV-treated sample. The observed dynamic changes are most likely associated with the increased crystallinity of the surface, where a decreased accessibility for the enzyme-catalyzed hydrolysis was found. Moreover, our NMR study provided further knowledge on how polymer chain conformation and dynamics of PET can mechanistically influence the enzymatic degradation.
Highlights
Polyethylene terephthalate (PET) is one of the most widely used plastic type, especially as packaging material for the food industry and as synthetic fibers for the textile industry (World Economic Forum, 2016; Geyer et al, 2017; PlasticsEurope, 2019)
We identified changes in enzymatic degradability and chain dynamics of PET caused by UV irradiation
The enzymatic degradation of post-consumer PET has emerged as an eco-friendly method for future applications in plastic recycling processes (Wei and Zimmermann, 2017)
Summary
Polyethylene terephthalate (PET) is one of the most widely used plastic type, especially as packaging material for the food industry and as synthetic fibers for the textile industry (World Economic Forum, 2016; Geyer et al, 2017; PlasticsEurope, 2019). Distinct conformations of PET segments derived by computational modeling and NMR experiments have provoked scientific discussions about the exact molecular mechanism of enzymatic PET degradation (Austin et al, 2018; Joo et al, 2018; Wei et al, 2019b). This knowledge would facilitate further exploration and engineering of enzyme variants toward enhanced PET hydrolytic activity, as well as of feasible pretreatment approaches to lower the degradation obstacle in terms of the polymer substrate
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