A research team in Japan has developed a method for the depolymerisation of PET (polyethylene terephthalate) using an alcohol and an inexpensive, readily available iron trichloride catalyst.
- This method can be applied to the selective chemical recycling of both textile and plastic waste mixtures.
- This exclusive chemical recycling of PET from plastic wastes offers a promising solution for achieving a circular economy.
THE CONTEXT: Plastic waste is a significant environmental issue that requires urgent attention. However, the rate of plastic reuse (material recycling) remains low, particularly in the case of chemical recycling into raw materials, a process known as chemical recycling.
- Polyesters, which consist of repeated “ester bonds” formed by the reaction of carboxylic acid and alcohol, are commonly used in plastic bottles and clothing. If these ester bonds could be completely broken, polyester could be reverted to its raw materials.
- Conventional methods, however, necessitate high temperatures and large amounts of acidic or basic substances. Therefore, a simple, cost-effective, and environmentally friendly method is highly sought after.
- Additionally, there is a global demand for the development of selective depolymerisation of polyester from plastic waste, especially from textile waste, which is a mixture of polyester and cotton.
THE WORK: The research team has now developed a method for acid- and base-free depolymerisation of PET bottles using ethanol and either ferric chloride (FeCl3) or ferric bromide (FeBr3), yielding diethyl terephthalate (DET) and ethylene glycol (EG) with high selectivity (98-99%).
- Ferric chloride, which is inexpensive and widely available, demonstrated superior catalytic performance at 160–180 ºC, comparable to their previous results using titanium catalysts.
- This method enabled the exclusive and selective depolymerisation of PET from textile waste, which comprises PET and a mixture of PET and cotton, yielding DET and EG while quantitatively recovering cotton waste. The catalyst also facilitated the selective depolymerization of PET from plastic waste, including polyethylene.
THE SIGNIFICANCE: The development of a straightforward method for the exclusive and selective depolymerisation of PET is particularly desired for the chemical recycling of textile waste.
- This method of exclusive chemical recycling of PET from plastic wastes offers a promising solution for achieving a circular economy.
THE RESEARCH: The research team led by Professor Kotohiro Nomura from Tokyo Metropolitan University.
- The work was supported by the JST CREST programme within the Research Area ‘Precise Material Science for Degradation and Stability’, and the Research Theme ‘Development of Bio-Based Advanced Polymers and their Depolymerization, Chemical Recycle’.
