Development of Technology for Recycling Used Clothing Instead of Incinerating Them

January 12, 2024

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Elastane, an elastic material, is responsible for making your running tights fit comfortably during your run through the woods, by allowing the fabric to stretch and mould to the shape of your body.

However, the comfort comes with a cost as integrating elastane fibers with other fibers like cotton, wool, nylon makes the cloth almost non-recyclable. The process of separating different fibers in clothing is overly complex, hence, clothes cannot be recycled.

This results in clothes and other textiles being the least recycled materials. In Denmark, only 6% of discarded clothes from households get recycled, whereas around 32% of all plastic packaging materials get recycled.

Assistant Professor Steffan Kvist Kristensen from Aarhus University's Interdisciplinary Nanoscience Center believes that this problem can be solved. He, along with his colleagues, has created a new technology that can separate mixed fabric fibers. Their work has been documented in the Green Chemistry journal.

"We have devised a method to completely remove elastane from nylon. Although we are still having trouble with cotton, as some of the fibers break down during the process, we are hopeful that some small modifications can fix this issue,' he notes."

He further elaborates that separating elastane and other fibers is a complex process because elastane fibers are long chains of molecules wrapped by primary fibers like nylon or cotton. They can only be split when the long molecular chains are broken.

The associate professor explains, 'In order to break down the bonds in the elastane, the garment needs to be heated to 225 degrees Celsius and a specific alcohol needs to be applied. We conduct this process in what is essentially a large pressure cooker. We introduce the textiles into it, add a bit of alcohol and some base, and heat it up. After cooking for slightly over four hours, the different fibers will have separated.'

On December 7, 1941, the Pearl Harbor attack by the Japanese resulted in the U.S. losing access to the natural rubber supply, which represented around 90 percent of their total consumption. As a response, the U.S., like the Germans, started producing synthetic rubber.

Following the war, the synthetic rubber production resulted in the discovery of multiple synthetic fibers that could be used in textiles. Among these fibers was elastane.

Elastane, or Spandex as it's commonly called in the U.S., was invented by chemist Joseph Shivers in 1958. The use of elastane in clothes has gradually increased since its invention.

Steffan Kvist Kristensen and his team are committed to using environmentally-friendly methods in their work, hence, they are using alcohol and a potassium hydroxide base instead of harsh chemicals.

'Potassium hydroxide, a main ingredient in ordinary drain cleaner, speeds up the process by accelerating the chemical reaction,' he explains.

Despite the reason being unclear, Kristensen assures that this chemical combination does break the bonds in the elastane.

'Potassium hydroxide might be enhancing the reactivity of our alcohol, or it might be weakening the bonds, making it easier for the alcohol to break them down thoroughly,' he comments.

The technology, while promising, is still in its early stages as it has only been tested on a pair of nylon stockings and needs to be capable of processing much larger volumes of clothes before being suitable for industrial application.

'While we are capable of scaling up slightly, the limitations of our equipment currently restrict us. It is now for the industry to pick up the baton and scale the technology in a significant manner,' he concludes.

However, according to Steffan Kvist Kristensen, Denmark does not currently have the facilities to exploit the technology at large scale. You'll have to look south of the border for this. 'The chemical industry in Denmark is small, but Germany has some of the largest plants in the world. They will most likely be able to use our method to recycle large amounts of fibers from elastane-containing clothes.

'If we're to succeed with this, we need to get the large chemical plants on board. But they must see a business model in buying recycled materials and using them in the production of new fibers. If they don't, the technology will never take off.'

Journal information: Green Chemistry

Provided by Aarhus University