Most everyday objects contain a secret tangle of different plastics. A mattress. A car seat. Your kitchen sponge. Unlike a PET bottle, which can be washed, shredded, melted, and reborn as something new, these items are made from layers and mixtures that refuse to cooperate when heated. They come out ruined instead of recycled. So most of the time, they get burned or buried instead. The materials are lost for good.
That could be changing, thanks to researchers at Kyushu University in Japan. They have developed a catalyst — a substance that speeds up chemical reactions — that can selectively break down one type of plastic called polyurethane, even when it is mixed with other plastics. The other materials, polyester and nylon, stay completely intact. They can then be separated out and recycled separately. The whole process happens in a single chemical step, using hydrogen gas heated to between 130 and 170 degrees Celsius — roughly hot enough to boil water on high.
Polyurethane is the sixth most widely used plastic on Earth. It shows up in sponges, textiles, mattress padding, and car seats. Unlike PET bottles, it does not melt when heated — so old methods of recycling do not work on it. Chemical recycling was possible, but older methods broke down the polyurethane and damaged the other plastics mixed in with it at the same time. Nothing could be saved.
The new catalyst changes that. Led by Professor Takanori Iwasaki at Kyushu University's Faculty of Engineering, the team combined an iridium-based catalyst with a phenolate salt additive and hydrogen gas. The result was a chemical reaction that cut polyurethane's bonds first, leaving stronger bonds in polyester and nylon untouched. Iwasaki calls this remarkable because it flips what every chemistry student learns — that weaker chemical bonds should always break before stronger ones. Here, the weakest bond of all gets cut first.
The researchers did not stop at lab samples. They tested the method on real products: a kitchen sponge, a piece of blended underwear containing polyester and nylon alongside polyurethane, a mobile phone case, and an end-of-life car seat. In every case, the polyurethane broke down into small molecules that could be reused, while the other plastics remained unharmed.
Iwasaki sees two industries that could benefit most: end-of-life vehicle recycling and mattress disposal. Both generate enormous volumes of mixed polyurethane waste that currently have almost no recycling options.
There is also a comfort angle. Japan's Shinkansen trains offer a concrete example. Newer models replaced polyurethane seat cushions with polyester ones because polyester is easier to recycle. But passengers noticed the difference — polyester is less comfortable. Iwasaki argues that if manufacturers can handle mixed plastics properly, they no longer have to choose between comfort and recyclability.
A major hurdle remains: cost. Iridium, the metal at the core of the catalyst, is rarer and more expensive than gold. The team is already working on finding cheaper alternatives and improving the catalyst's efficiency. Iwasaki says the goal is not just plastic recycling — the ability to selectively break one chemical bond in a complex mixture could have applications far beyond waste.