Polymorphism control of polyethylene terephthalate (PET) degradation product via mechanochemistry leads to accelerated microbial degradation†

Widespread usage of single-use plastics such as polyethylene terephthalate (PET) has heavily contributed to a global plastic pollution crisis, necessitating the improvement and development of recycling methods. We previously established a chemo-microbial degradation process for post-consumer PET plastic, consisting of PET depolymerization to form bis(2-hydroxyethyl) terephthalate (BHET) followed by the complete degradation of BHET by a bacterial consortium found to synergistically degrade PET and BHET. The BHET produced during PET depolymerization consists of two polymorphic forms, the α and δ forms. This work investigates the effect of BHET polymorphism on microbial degradation to further optimize the chemo-microbial process. Reversible interconversion methods for BHET polymorphs were effectively developed using mechanochemistry, achieving pure α and δ forms by modulating milling conditions. When inoculated with the bacterial consortium, the α form was degraded faster than the δ form, indicating solid polymorphism is a significant factor for the biodegradation level. This work paves the way to optimize the chemo-microbial process for an increased degradation rate of post-consumer PET and furthers the effort for sustainable plastic recycling methods.