Polyester is a big environmental problem. The fabric is used to make everything from shirts and pants to socks and underwear, and since it’s made of plastic—specifically polyethylene terephthalate, or PET, the same type used in water bottles—it doesn’t break down. It’s also incredibly difficult to recycle, especially when blended with other fabrics like cotton. But now, with the help of a once-common household ingredient used in baking, researchers have found a way to break down poly-cotton blends so that both the plastic and cotton can be reused.
The market for cotton-polyester blends, or poly-cotton, is massive, estimated at $15.9 billion globally in 2023 and expected to keep growing. It’s also a big part of textile pollution, accounting for half of global textile waste. Though polyester and cotton can each be recycled on their own, it’s more difficult once they’re blended. The typical process of melting polyester degrades the cotton fibers so that they are no longer reusable; it also releases pollution. Using chemical recycling, with acids and solvents to dissolve the plastics, creates hazardous by-products that can get into the environment and contaminate water streams.
Researchers at the University of Copenhagen were looking for a “green” way to recycle this fabric, and PET in general, without producing any other harmful effects. Called the Jiwoong Lee group, the researchers often look for ways they can use CO2 in chemical reactions, because it’s a gas that doesn’t create any other waste once used. When trying out different methods, they stumbled upon hartshorn salt, also called ammonium bicarbonate or baker’s ammonia—a once-common leavening agent for baking before baking powder became popular.
Hartshorn salt is made up of ammonia, CO2, and water. When heated, the ammonia and CO2 react to break down polyester while leaving the cotton unharmed. “To the best of our knowledge, until now there was no way to safely extract cotton [from PET],” says Shriaya Sharma, a PhD student in the research group and one of the authors of the paper published in the journal ACS Sustainable Chemistry & Engineering.
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