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Optimising the Depolymerisation of PET Fleece Microplastics Through Microwave Irradiation
Summary
Researchers optimized microwave-assisted glycolysis of PET fleece microplastics to produce bis(2-hydroxyethyl) terephthalate (BHET) for chemical recycling, varying catalyst loading, irradiation time, and reaction temperature. Optimal conditions of 2 mg catalyst, 3-minute irradiation, and 250°C maximized BHET yield as measured by HPLC. The study demonstrates a potential pathway for recovering PET fleece microfibers—a significant source of aquatic microplastic pollution—before environmental release.
Polyethylene terephthalate (PET) is one of the world’s most used plastics. Amenable to both mechanical and chemical recycling processes, PET is also commonly recycled. Chemical recycling processes of PET include glycolysis, which produces bis(2-hydroxyethyl) terephthalate (BHET); this is then re-polymerised to form new PET. One novel method for PET glycolysis involves microwave irradiation of PET water bottles in the presence of a catalyst and, notably, a microwave absorber. The research presented here investigates the optimisation of this novel method for PET fleeces. Samples were prepared using constant amounts of solvent, fleece, and microwave absorber. The conditions chosen to be varied and optimised were catalyst loading, irradiation time, and reaction temperature. Multiple variations of these conditions underwent the course of experimentation and were analysed through high performance liquid chromatography (HPLC) to determine their composition. The conditions used in samples that produced the highest yield of BHET were determined to be optimal. These conditions were found to be a catalyst loading of 2 mg, an irradiation time of 3 minutes, and a reaction temperature of 250°C. It has recently been observed that a substantial portion of microplastic pollution in bodies of water (which greatly impacts the environment) can be attributed to fleece microfibres, which are composed of PET. Through the capture and depolymerisation of fleece microfibres before release, this research could play an important role in the reduction of the amount of PET microfibre polluting the world’s oceans in the future.