Korean research team develops process to make a whole new material using discarded PET

[Seoul, South Korea] Plastic is hard but flexible, waterproof and light. Due to its unique nature, plastic is widely used worldwide in a variety of fields, including clothing, food, healthcare and automotive industries. However, these robust properties are not easily decomposed in nature, which is causing serious damage to the environment.

Due to the nature of plastics, it is difficult to replace plastics with other substances throughout the industry. Therefore, it is very important to increase the plastic recycling rate. The most commonly used plastic is PET. Typical PET recycling methods include collecting and classifying PETs, re-using them after cleaning, using heat generated by incineration of PETs, and decomposing PETs by physical or chemical methods and reproducing PETs again.

Recently, Professor Kim Kyung-hun’s research team (Korea University Bioscience University) and Professor Han Jung-woo’s research team (Pohae University) developed a process to efficiently decompose PET waste using eco-friendly and biocompatible catalysts. It is meaningful in that it is a process that can produce new materials using waste plastic, rather than collecting used and discarded plastic and recycling it back into plastic.

The process developed by the research team consists largely of PET decomposition and biological conversion process. The biological conversion process is a fermentation process using microorganisms, which cannot be achieved smoothly if there are substances that hinder microbial growth and activity. The research team considered how to combine chemical and enzymatic decomposition processes. Research team needed biocompatible catalysts that are eco-friendly and do not affect biological processes. The team became interested in a catalyst called “Betaine”, which is biosynthesized to protect cells in response to environmental stress mechanisms such as osmotic pressure, high temperature, and dehydration in living organisms. They predicted that Betaine, as a bilateral ion, has both cations and anions in a substance, so it would be able to react similarly to ionic liquids that are now considered effective in PET decomposition.

Using Betaine, the research team was able to decompose 80% of injected PET into oligos. They were also able to simplify the process because only the final reactants had to be separated after the fermentation process without having to separate the products for each reaction every time. In addition, it is easier to separate the final substance because it does not use metal ions or organic compounds that interfere with the enzyme reaction and the fermentation process by microorganisms. As a result, the process is simpler and more economical because only the final reactants can go through a separate purification process without separating the reactants every moment. If discarded PET can be used as a raw material to produce new materials, it marks a milestone in PET recycling. To this end, economic analysis of the process , considering various factors, would be needed.

Source: One-Pot Chemo-bioprocess of PET Depolymerization and Recycling Enabled by a Biocompatible Catalyst, Betaine
Dong Hyun Kim, Dong Oh Han, Kyu In Shim, Jae Kyun Kim, Jeffrey G. Pelton, Mi Hee Ryu, Jeong Chan Joo, Jeong Woo Han, Hee Taek Kim, and Kyoung Heon Kim, ACS Catalysis 2021 11 (7), 3996-4008, DOI: 10.1021/acscatal.0c04014

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