A New Catalyst for the Recycling of Mixed Plastics

Most mixed plastic waste cannot be effectively recycled because different types of plastic do not mix well with one another. This situation makes incineration or landfilling the main options, while also causing valuable materials to be wasted.

On July 9, 2026, a Japanese research team presented a potential solution in the journal Angewandte Chemie International Edition. In the study, which was selected as a “Hot Paper” by the journal, the team used a newly developed catalyst and hydrogen gas to selectively decompose polyurethane (PU) in mixed plastic waste. During this process, the polyester and polyamide materials present alongside it remained unchanged and were preserved in a usable state for recycling through further processing.

Professor Takanori Iwasaki from Kyushu University's Faculty of Engineering explains, “Although PU is the sixth most common polymer in the world, used in textiles, sponges and automobile seats, it largely falls outside recycling systems. Unlike PET, it does not melt when heated. Therefore, we need to break its chemical bonds directly.”

The main challenge here is that PU is almost always mixed with or bonded to polyester and nylon in real-world products. Existing chemical methods can break down PU, but they also damage the other materials during the process. This makes it impossible to recover the materials separately from one another.

Iwasaki and researchers from the University of Tokyo and Japan's National Institute of Advanced Industrial Science and Technology (AIST) found a way to overcome this problem. The team combined an iridium-based catalyst with a phenolate salt, which acts as an activator for the iridium catalyst, and used hydrogen gas at a temperature of 130–170°C. This successfully decomposed the PU in the mixed plastic waste, while the accompanying polyester and nylon remained completely unchanged.

Iwasaki says, “In my opinion, the most striking point is that this method reverses the fundamental knowledge that every undergraduate student who studies organic chemistry learns.” In standard chemistry, esters are more reactive than amides, and amides are more reactive than urethanes. Accordingly, polyester should decompose before nylon, and nylon before PU. “However, by combining the iridium catalyst with the right additive, we completely reversed this order. The bond with the lowest reactivity breaks first, while the more reactive bonds remain untouched.”

In addition to laboratory experiments, the team also tested the method on real commercial products. A kitchen sponge and a blended undergarment, both containing PU as well as polyester and nylon, were successfully processed. While the PU was broken down into reusable components, the polyester and nylon retained their structure. The method also produced successful results on a mobile phone case and an end-of-life automobile seat.

The research team notes that cost and scalability issues are still being resolved. Iridium, which forms the basis of the catalyst, is a metal that is rarer and more expensive than gold. Finding more cost-effective alternatives and increasing catalytic efficiency are of great importance for the next stages.

Iwasaki continues by saying, “Plastic recycling is just the beginning,” adding: “As an organic chemist, what excites me most is the ability to selectively alter the rules of chemical reactivity. I hope this will enable more bridges to be built between fundamental chemistry and real-world problems, ranging from plastic waste to pharmaceutical synthesis and beyond.”