Chemoenzymatic Synthesis and Degradation of Plastics

The development of a carbon-based bioeconomy for synthesis and degradation of polymers has gained importance over the years. Research efforts have been made to develop green routes to produce bio-based material from biomass as well as environmentally friendly ways to synthesize and degrade polymers. Enzymes are biocatalysts that are capable of performing reactions beyond their intended purpose. The work presented in this thesis focused on using biocatalysts for novel reactions to produce bio-plastics as well as degrade synthetic polymers. In Paper I, a decarboxylase was used to perform the fixation of CO2 under mild conditions to produce the platform chemical 2,5-furandicarboxylic acid (FDCA). In Paper II, a closed-loop approach for the production of bio-based polyesters and their enzymatic degradation was investigated. Moreover, the difference of catalytic activity towards different polymer conformations was noted and further investigated in Paper III. Here, the conformational landscape to match enzyme to substrate was explored. The model substrate for this project was post-consumer PET bottles since is one of the most used polymer worldwide. The substrate conformation affected the catalytic activity of the enzymes significantly hence, in Paper IV, the physical and chemical characteristics of various PET-based substrates was investigated to better understand the factors that will yield a high reaction efficiency for polymer depolymerization. Finally, the results obtained so far were used in Paper V to show that plastic degrading enzymes can be used for microplastic degradation in human blood as a proof-of-concept. In summary, the work in this thesis showed the potential of using enzymes as catalysts for the production of platform chemicals through CO2 fixation and for polymer degradation initiating an attractive path to close the loop in a bio-economy for polymer materials.