Cyanamide as a Highly Efficient Organocatalyst for the Glycolysis Recycling of PET

Due to the antibiodegradable properties, numerous plastics have been accumulated in the ecosystem and aggravate ecological pollution. Poly (ethylene terephthalate) (PET) is among the most used plastics. Glycolysis of PET is a useful approach to solve the waste PET pollution and obtain bis(2-hydroxyethyl) terephthalate (BHET). In this paper, waste PET was efficiently depolymerized through glycolysis catalyzed by cyanamide. In particular, compared with the previously reported catalyst, cyanamide is more readily available and can be used directly in catalysis without a complex preparation process. Under optimal conditions, PET was completely depolymerized with up to nearly 100% BHET yield. Even at a temperature as low as 150 °C, a good BHET yield can be obtained. The application potential of this glycolysis procedure was demonstrated by its excellent performance in the glycolysis of various real PET wastes like transparent and opaque PET samples and polyester foam and by the high quality of the obtained BHET products. The mechanism was studied by 1H NMR analysis, and DFT calculations showed that the higher activity of cyanamide than its trimer, melamine, is due to the stronger hydrogen bonds formed between cyanamide and PET or ethylene glycol.