When you go running in the woods in your running tights, elastane (氨纶) is the reason why they fit you so comfortably. Elastane is an elastic material that allows the fabric to stretch and adapt to your body.
But when elastane fibres are mixed with cotton, wool, nylon or other fibres, as is the case in many clothes today, the clothes become almost impossible to recycle. It is extremely difficult to separate out the different fibres, and therefore the materials in the clothes cannot be recycled.
But this may change, says Assistant Professor Steffan Kvist Kristensen from the Interdisciplinary Nanoscience Center at Aarhus University. Together with a number of colleagues, he is behind a new technology that can separate out fibres in mixed fabrics.
"We've developed a method to remove elastane completely from nylon. We're not quite there yet with cotton, because some of the cotton fibres are broken down in the process. But we believe that, with some minor adjustments, we can solve this problem," he says.
It is not easy to separate elastane and other fibres once they have been woven(编织) together. Clothes are made by winding the main fibres, such as nylon or cotton, around the elastane fibres, which consist of long chains of molecules (分子). The fibres only break apart if we break the long chains of molecules, explains Steffan Kvist Kristensen.
By heating the clothes to 225 degrees Celsius and adding a specific alcohol, the researchers have found a method to break down the bonds in elastane chain. When this happens, the chains fall apart and the materials separate. "The whole process takes place in what is in effect a large pressure cooker that we feed the clothes into. We then add a little alcohol and a potassium hydroxide(氢氧化钾) base and heat it up. Then we let it cook for just over four hours, and when we open the lid again, the different fibres will have been separated." says Steffan Kvist Kristensen.
So far, Steffan Kvist Kristensen and his colleagues have only experimented with two nylon stockings at a time. The technology is therefore not yet ready for application at industrial scale.