New catalyst could make mixed plastic waste recyclable in one chemical step Sadie Harley Scientific Editor Andrew Zinin Chief Editor Ever wondered where your plastics end up? A PET bottle can be washed, shredded, melted and given a second life. But most everyday items—toys, mattresses, car seats—are made from different plastics that refuse to mix when melted, producing unusable, contaminated material.

Sorting is difficult and expensive, so most mixed plastic waste ends up burned or buried, and the materials are lost for good. A Japanese research team has reported a potential solution in Angewandte Chemie International Edition. Using a newly developed catalyst and hydrogen gas, they selectively broke down polyurethane (PU) in mixed plastic waste, leaving coexisting polyester and polyamide materials intact for further processing and recycling.

"PU is the sixth-most widely used polymer, found in textiles, sponges and car seats, yet it remains largely outside the reach of recycling systems," explains Professor Takanori Iwasaki of Kyushu University's Faculty of Engineering. "Unlike PET, it does not melt when heated, so we need to break the chemical bonds directly." The challenge is that PU is almost always blended or bonded with polyester and nylon in real-world products. Existing chemical methods break down PU but damage the other materials in the process, making separate recovery impossible.

Flipping the usual chemistry Iwasaki, together with researchers at the University of Tokyo and Japan's National Institute of Advanced Industrial Science and Technology, found a way around this. By combining an iridium-based catalyst with a phenolate salt—an activator for iridium catalyst—and using hydrogen gas at 130–170°C (266–338°F), the team successfully degraded PUs in mixed plastic waste while coexisting polyester and nylon remained completely unchanged. "What I find most remarkable is that it overturns what every undergraduate learns in organic chemistry," notes Iwasaki.

In standard chemistry, esters are more reactive than amides, and amides more reactive than urethanes. This means polyester should break down before nylon, and nylon before PU. "By combining iridium catalyst and the right additive, we flipped that sequence entirely.

The least reactive bond gets cut first, while the more reactive ones are left untouched." From lab samples to products Beyond laboratory experiments, the team tested the method on real commercial products. A kitchen sponge and blended underwear, containing PU alongside polyester and nylon, were successfully treated, with the PU breaking down into reusable components while the polyester and nylon stayed intact. The method also worked on a mobile phone case and an end-of-life car seat.

As the process achieves material separation and chemical recycling in a single step, it opens new possibilities for waste long considered too complex to handle. The team sees particular promise in end-of-life vehicle recycling and mattress disposal, two industries generating enormous volumes of PU waste with limited recycling solutions today. Comfort without the recycling trade-off The research also speaks to a broader tension in materials design.