Mechanochemical and mechanobiological recycling of postconsumer polyethylene terephthalate (PET) plastics under microwave irradiation: a comparative study

Exploring new solutions to improve the environmentally friendly degradation of fossil based postconsumer plastic waste is key in the development of effective techniques to increase the efficiency of plastics degradation while using mild, green depolymerization conditions. In this context, we introduce a novel, ultrafast mechanical pretreatment for postconsumer (PC) polyethylene terephthalate (PET) plastics that is based on a dissolution/reprecipitation approach under microwave (MW) irradiation. Fourier transform infra-red (FTIR) and Differential scanning colorimetry (DSC) analyses indicates a significant increase, up to 3.78 in the carbonyl index and a 2-fold decrease in crystallinity index of the pretreated PC PET sample when compared to the untreated one. Degradation efficiency of both untreated and pretreated PC PET was evaluated using enzymatic and MW assisted chemical degradation techniques. Results show that following MW assisted hydrolytic depolymerization, pretreated PC PET conversion rate of 95 % and terephthalic acid (TPA) monomer yield of 87.4 % were obtained and were significantly higher than that of untreated PC PET. While the proposed pretreatment approach did not show a significant improvement on the enzymatic degradation of PC PET, it did result in a 1.2-fold increase in the pretreated PC PET conversion rate, yielding solely TPA as a value-added monomer. This presents an advantage in the economic cost of the degradation process if applied on a larger scale.