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“When clothes are exposed to sunlight and are washed and dried repeatedly, the molecules which color the cloth begin to detach from the surface of the material and the colors fade,” says Patrick McGowan, a chemistry professor at the University of Leeds.

“If this happens in your washing machine, the molecules may reattach to the other items that they’re being washed with—hence your white shirts turns grey and your black top slowly fades and loses color,” adds McGowan, who is cofounder of DyeCat, a company developing the technology, which offers a more environmentally friendly alternative to more conventional methods currently used for dyeing clothes.

Details of the work are reported in the journal Angewandte Chemie and Nature Chemistry.

“The DyeCat technology turns the way that textiles are colored on its head so this doesn’t happen. Currently, when clothing is made, the fabrics are usually dyed using chemicals in water baths and it is during this process colored molecules attach themselves to the fabric and this gives the color we see. But this uses lots of energy and water and is costly and time-consuming,” says McGowan.

“In the DyeCat process we do things differently, we color the fiber itself—the bit that ends up making up the fabric—as the fiber is made, meaning that the color is ‘locked in’ and will never wash out or fade like the traditionally dyed materials.”

Currently, many of the clothes produced around the world include polyester, a type of polymer made from oil. But with oil and gas supplies dwindling and an increasing recognition of the environmental damage that can be caused by the extraction and use of oil, the need for alternative materials made from renewable sources has never been greater.

DyeCat’s technology uses another type of polymer called PLA, or polylactic acid, which is an alternative to oil-based polymers. PLA is derived from renewable sources, such as maize, and is biodegradable, but until now, it has not been used extensively in the commercial production of fabrics, in part because of the problems in dyeing it.

Researchers found a way around this problem. “We made a chemical catalyst to which different colored dyes are added. When the catalyst is added to the lactic acid derived from corn starch or cane sugar, it turns the acid into the PLA polymer and the color becomes part of the polymer at the same time,” says McGowan.

“Because the molecular structure of the PLA is altered at this early stage—as opposed to the polymer being dyed later in a chemical wash—the color is permanent.”

The colored polymers can be blended with other fibers into textiles and the colors show through, and because PLA occurs naturally, the fibers are biodegradable meaning the clothes can be composted when finished with.

“We have other pieces of technology we are working on, including one that allows us to dye materials that are thought of as ‘undyeable’ and making existing dyeing processes for things like hair dyes fair better.”

More news from the University of Leeds: www.leeds.ac.uk/news