A group of young chemists from the University of Copenhagen has invented a simple solution using baking powder to recycle polyester, a blend of plastic and cotton.
Polyester is the second most used textile in the world with 60 million tonnes produced globally every year and 85% ending up in landfills or being incinerated. Conventional recycling methods often prioritise preserving the plastic, resulting in a loss of cotton fibres. Such methods can often be costly and complex, generating metal waste due to the use of metal catalysts.
The Copenhagen team put shredded fabrics into a mixture of Hartshorn salt (baking powder) and a non-toxic solvent. This is heated up to 160 degrees Celsius and left for 24 hours.
‘The result is a liquid in which the plastic and cotton fibres settle into distinct layers – it’s a simple and cost-effective process,’ explains Shriaya Sharma, a doctoral student of the Jiwoong Lee group at the Department of Chemistry and co-author of the resulting study.
The hartshorn salt, also called ammonium bicarbonate, is broken down into ammonia, CO2 and water. The combination of ammonia and CO2 acts as a catalyst, triggering a reaction that breaks down the polyester while preserving the cotton fibres. Although ammonia is toxic on its own, when combined with CO2 it is safe for use. Due to the mild nature of the chemicals involved, the cotton fibres remain intact.
Sharma’s colleague and lead author Yang Yang says the textile industry urgently requires a better solution to handle blended fabrics like polyester/cotton. ‘Currently, there are very few practical methods capable of recycling both cotton and plastic, it’s typically an either-or scenario.
‘However, with our newly discovered technique, we can depolymerise polyester into its monomers while simultaneously recovering cotton on a scale of hundreds of grams, using an incredibly straightforward and environmentally friendly approach. This traceless catalytic methodology could be the game-changer.’
The new recycling method works on PET plastic alone, as well as on PET and cotton blended materials.
‘If we throw dirty plastic waste in a container, we still get good quality cotton and plastic monomer out of it,’ says Sharma. ‘This can even be a plastic bottle with juice residue still in it. We just put it in and begin the reaction. It still works.’
While the method has only been tested at laboratory level, the researchers are in contact with companies to test the method on an industrial scale.