UV Pretreatment Impairs the Enzymatic Degradation of Polyethylene Terephthalate

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 1 H 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 (T 1ρ ), 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 enzymecatalyzed 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.

Sustainable, self-cleaning, transparent, and moisture/oxygen-barrier coating films for food packaging

“…S3). 52,53 Thus, the first coating layer, i.e., positively charged CsWs, adhered strongly to the UV- Please do not adjust margins Please do not adjust margins treated PET surface via NH 3 + -mediated charge-dipole and cation-π interactions. Following the introduction of the first layer, the opposite electrical charges and the different aspect ratios of CsWs and CNFs led to the formation of subsequent tightly bonded layers, resulting in a stable coating and excellent barrier properties.…”

Analytical methods for the investigation of enzyme‐catalyzed degradation of polyethylene terephthalate

“…As an example, 0.3 mg·mL −1 of nanoPET produced using PET from different sources (from granulate, film, or fibers) was treated with increasing concentrations of TfCut2 (up to 50 μg·mL −1 ): The turbidity of the reaction mixture reached a value < 5% after 30 min of incubation at 60 °C with the exception of the one produced from recycled PET granulate. This nanoparticle preparation corresponds to a PET concentration of 8.6 μ m and a concentration of ester bonds of 1.57 m m (considering an estimated mean degree of polymerization of amorphous PET of 181.7 units and a MW of 35 000 g·mol −1 ) [ 25 ]; anyway, only the ester bonds exposed on the nanoparticle surface are available for the enzymatic hydrolysis. To avoid sedimentation of nanoparticles with a diameter > 100 nm during the reaction and to increase the reproducibility of the measurements, nanoPET were immobilized onto 0.9% agarose matrix with pore sizes between 100 and 250 nm [ 32 ].…”

“…The NMR analysis allows the determination of the degree of polymerization of PET which, correlated with the amount of weight loss of the sample during the enzymatic treatment, allows the discrimination between the endo‐ and exo‐type cleavage of the polymer [ 24 ]. In addition, the analysis of the PET properties at an atomic level (e.g., the determination of the ratio between the gauche and trans conformations in the polymer, which correlates with its degree of crystallinity) can be performed by solid‐state NMR methods [ 25 , 26 ]. These methods give an in‐depth assessment of the effect of enzymatic treatment on the polymer structure and are most suited for a detailed mechanistic investigation of the mode of action of PET hydrolases.…”

Biotechnology of Plastic Waste Degradation, Recycling, and Valorization: Current Advances and Future Perspectives

“…Particularly, UV radiation is an important factor for plastic biodegradation since it could activate carbon backbone polymers so that relevant enzymes could carry out initial oxidation that is essential for subsequent processes. [19] Biotic biodegradation of polymers normally involves four stages: (1) biodeterioration, which is fulfilled by the assistance of enzymes excreted by microbes, or done by involving external factors, such as UV irradiation, [20] resulting in the modification of plastic waste properties; (2) biofragmentation, a fundamental stage involving hydrolysis and/or oxidation induced by secreted enzymes and the cleaving of high-molecular-weight polymers into oligomers or monomers with a smaller size, which are then able to enter microorganisms and facilitate the following stage;…”

“…[28] For the degradation mechanisms, one recent finding is that UV irradiation impairs the hydrolytic efficiency of polyester-degrading enzymes, especially for PET, which resulted in a negative effect on PET biodegradation. [19] Similarly, weathered PET experienced worse biodegradation because enzymes could only be functional to amorphous PET. More chain breaks, which lead to a higher crystallinity of the plastic, also have a negative influence on the biodegradation of PET.…”