Think of clothing that's marketed as "green," and you might picture an organic cotton shirt. But if you want to wear something that does the best job fighting climate change, try a self-cleaning sweater instead.
For most clothing, no matter how it was made or how many thousands of miles it traveled around the world to reach a store, the biggest part of its carbon footprint usually comes from the time it spends in the laundry or at the dry cleaners. That may change as clothing begins to automatically clean itself, using nothing but light.
The newest self-cleaning fabric is cashmere, a delicate material that usually gets cleaned in an expensive, energy-intensive, and sometimes toxic process at a dry cleaner. By coating cashmere with an invisible, nano-thin layer of anatase titanium dioxide, researchers in Hong Kong have created fabric that doesn't resist stains, but makes them disappear.
If the fabric is placed in light for 24 hours, any dirt, bacteria, or stain—even coffee or red wine—automatically goes away, thanks to a chemical reaction triggered by the light.
The researchers have been developing self-cleaning materials since 2002, starting with cotton and wool. Cashmere was the next step, since it's difficult to clean. "Cashmere is a sensitive protein and can be easily damaged and therefore it is notoriously expensive to clean," says Walid Daoud from City University of Hong Kong's School of Energy and Environment.
It wasn't easy to get right. "It is a delicate operation because of the risk of spoiling the cashmere in the process," Daoud says. "How to apply nano-sized photocatalysts to cashmere and retain its delicate characteristics was a huge challenge."
Now, the researchers say the technology is ready to start making it into actual clothing, assuming—and this could be a catch—that tests continue to show that there are no adverse effects on health from the nanoparticle coatings. So far, preliminary tests have shown that the material is safe. Tests have also shown that the coating is durable; the cleaning effect would last as long as the fibers are intact.
"It should reach the market very soon," says Daoud. "We are currently working toward transfer of the technology to the industry." A self-cleaning sweater might only cost 1% more than usual. Ultimately, the technology could be used in all clothing—eliminating, for laundry in the U.S. alone, more than 179 million metric tons of CO2 emissions every year.