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Scientists at Tokyo Metropolitan University have developed a new chemical process which upcycles polyesters

by | Oct 11, 2023

Scientists at the Tokyo Metropolitan University have had a breakthrough with their research focused on repurposing plastic waste into innovative building blocks for organic chemistry.

Before the scientists created this new process, recycling polyesters, such as the polyethylene terephthalate (PET) which is found in plastic bottles, was a much more difficult process, as it involved power to heat the plastic to the required temperature, or strong alkaline conditions were needed which would generate chemical waste. This chemical reaction is not environmentally friendly and the end product is only intermediate compounds which go into forming the same products which they came from. This process is wasteful and is often economically unviable.

This is where the scientists saw the need to make a change and they developed a way to up-cycle the plastic waste. By breaking the closed loop cycle, they discovered a way to create compounds from plastic waste, these compounds are more valuable and useful for society. This development of an open loop system is called upcycling and is an excellent break through and it shows an innovative strategy to help the recycling industry evolve into a greener society.

The reaction was developed by the research team, led by Associate Professor Yohei Ogiwara and Professor Kotohiro Nomura from the University, and the method is almost completely waste-free. Through using morpholine, a cheap solvent which is excellent at synthesising a vast range of compounds, and also using a small amount of titanium-based catalyst, this reaction will turn polyesters into morpholine amides. These morpholine amides can then be converted into intermediate compounds which can make more polyester, which is how the product can be recycled, or the amides can be reacted to produce ketones, aldehydes and amines, which are all necessary kinds of chemicals, which can be used to make a large variety of other, more valuable compounds, and this is how the plastic can be upcycled.

The benefits of this process involve the reaction not requiring expensive reagents or tough conditions and the reaction produces next to no chemical waste. Furthermore, the yield is very high, the unreacted solvent is easily collectible, plus the researchers discovered that only a small amount of catalyst was needed to enable the reaction at a good speed and it was simple filtration which separated the product from the waste. Other points which the research team highlighted as important advancements, is that the main reaction does not require extra pressure to take place, which means that the reaction does not require a specific vessel or device. This results in the reaction being scalable, especially in the lab. The researchers demonstrated these factors through running a test with 50g of PET material from a PET bottle, they reacted it with morpholine, and the result was receiving more than 70 grams of morpholine amide and a yield of 90%.

The scientists behind this project have achieved their aim of breaking the costly closed-loop recycling loop of plastic waste, through making upcycling possible for the plastic recycling chain and enabling the creation of more valuable products. Now the scientists are looking forwards to developing their discovery further, because as the global plastic waste problem becomes more acute, new strategies will be required to deal with it. So as this method is a low-cost, waste-free, upcycling option, the team is hoping to apply their method to bigger projects and aim to turn polyester into speciality chemicals.

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