Researchers Develop Efficient Polyester Recycling Technology

The problem with advanced, aka chemical, recycling has never been about the technology — it works and has actually been around for several decades — it’s the economic viability and scalability of the process that many question. Researchers at Washington State University (WSU) may have an answer: A catalytic process that breaks down polyester in about an hour at moderate temperatures. If scaled up, say the researchers, it could facilitate efficient plastics recycling.

Using a sequential chemical sorting method, the researchers were able to separate up to 100% of the basic ingredients of polyester, including from mixed plastics. The monomers could be used to produce new, high-quality plastics that are as good as virgin resins, writes Tina Hilding in a news release on the university website.

The research is published in the journal, Cell Reports Physical Science.

High yields under mild operating conditions

“The catalyst works very well and is very efficient, so we got very high yields, and the operating conditions are mild,” said Hongfei Lin, corresponding author and a professor in WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering.

The researchers used an inexpensive catalyst in methanol to break down one type of polyester — polyethylene terephthalate (PET) — into its monomers, dimethyl terephthalate and ethylene glycol. They were able to completely break down the PET in an hour at 160°C (320°F) to its monomers. The sequential catalytic process also enabled the researchers to extract the monomers from the PET, even when the plastic was mixed in with other materials, such as nylon, polyethylene, and polypropylene. They also had success breaking down the PET in difficult-to-recycle multilayer plastic films, such as vacuum-sealed storage bags.

Related:Chemical Recycling Just Isn’t Feasible

The method also worked with other types of polyesters, such as polylactic acid (PLA) which is used in disposable cutlery.

Polymer that's as good as new

Converting polyester back to its constituent monomers and re-synthesizing them results in a brand new polymer, said Lin. “The quality is going to be the same as the polymers when they are first made — and that’s the uniqueness about chemical recycling.”

In addition to WSU, the project included researchers from Pacific Northwest National Laboratory and the University of Washington. The work is supported by the National Science Foundation.