Non-Hydrolyzable Plastics – An Interdisciplinary Look at Plastic Bio-Oxidation

• Published in: Trends in biotechnology (Regular ed.) 2021-01, Vol.39 (1), p.12-23
• Main Authors: Inderthal, Hedda, Tai, Siew Leng, Harrison, Susan T.L.
• Format: Article
• Language: English
• Subjects: Bacteria; Biodegradability; Biodegradation; Carbon; chain-flexibility hypothesis; Enzymes; Flexibility; High density polyethylenes; Interdisciplinary aspects; Macromolecules; Mineralization; Molecular weight; Oxidation; Physics; plastic biodegradation; Plastic debris; Plastics; Polyester resins; Polyesters; Polyethylene; Polyethylene terephthalate; Polyethylenes; Polymer blends; polymer degradation; Polymers; Polypropylene; Polystyrene; Polystyrene resins; Polyvinyl chloride; Waste management
• ISSN: 0167-7799; 1879-3096
• DOI: 10.1016/j.tibtech.2020.05.004

Enzymatic plastic conversion has emerged recently as a potential adjunct and alternative to conventional plastic waste management technology. Publicity over progress in the enzymatic degradation of polyesters largely neglects that the majority of commercial plastics, including polyethylene, polypropylene, polystyrene and polyvinyl chloride, are still not biodegradable. Details about the mechanisms used by enzymes and an understanding of macromolecular factors influencing these have proved to be vital in developing biodegradation methods for polyesters. To expand the application of enzymatic degradation to other more recalcitrant plastics, extensive knowledge gaps need to be addressed. By drawing on interdisciplinary knowledge, we suggest that physicochemical influences also have a crucial impact on reactions in less well-studied types of plastic, and these need to be investigated in detail. Significant progress has been made in understanding the enzymatic degradation of hydrolyzable plastics with heteroatoms in their backbone structure, but information about the mechanisms and limiting factors for reactions of plastics containing C–C backbones is lacking.These plastics have been less well studied, and knowledge gained in related fields is invoked to propose reaction characteristics.Macromolecular architecture has been shown to govern enzymatic degradation of hydrolyzable plastics as well as abiotic reactions in polymers. We propose that this is applicable to all types of plastics as a determining factor according to the chain-flexibility hypothesis.Thermostable laccase mediator systems are promising enzyme system candidates.