A few hours of sunshine cleans specially treated cotton fabrics
Cleaning clothes usually requires soap and water to remove stains and smells, and a tumble in the dryer or an afternoon on the clothesline to dry. The time and energy needed to turn a heap of dirty laundry into a pile of clean clothes might make people wish for clothes that just clean themselves.
That wish is a step closer to coming true. Recent experiments show that cotton fabric coated with the right mixture of chemicals can dissolve stains and remove odors after only a few hours in the sun.
“The technology can be applied to all kinds of fabrics and their related products,” says materials scientist Mingce Long. He helped develop the treated cotton with his colleague Deyong Wu, both of China’s Shanghai Jiao Tong University.
The handy fabric gets its self-cleaning abilities from a chemical mixture that coats the cotton threads. The coating includes substances known as photocatalysts, which trigger chemical reactions in light. One of those photocatalysts, called titanium dioxide, helps sunscreen block the sun and is used as tattoo ink. Another, called silver iodide, is used for developing photographs.
Researchers have previously shown that titanium dioxide mixtures could remove stains in clothes — but with exposure to ultraviolet, not visible, light. (The waves of ultraviolet light are more energetic and shorter than those of visible light.) Other studies have demonstrated that silver iodide can speed up chemical reactions in sunlight.
“We knew that self-cleaning cotton fabrics with titanium dioxide coating had already been developed, but they cannot work, or they work weakly, under sunlight,” Long says. “If we want to use the fabrics in daily life, we must develop cotton that cleans itself under daylight.”
Long and Wu created just such a fabric, working for years to perfect the recipe for a liquid dip that left cotton coated with the titanium dioxide mixture. Then they added particles of silver iodide, which boosted the fabric’s self-cleaning ability in the sun. In laboratory tests, their creation was nearly seven times better at removing stains (and killing bacteria lurking in the clothing) than titanium dioxide alone.
The scientists can’t start selling their self-cleaning cotton just yet; scientists still need to make sure the coated cotton won’t harm those who wear it. Although titanium dioxide is used in some foods, recent experiments have shown that it can cause health problems if it gets in the lungs. So before the material can be worn, scientists need to find a way to make it safe.
Still, Long says that he hopes to wear self-cleaning clothes one day — and avoid having to do laundry. “Someday in the future, when I walk on the street,” he says, “I hope people are wearing self-cleaning clothes that originated from my technology.”
POWER WORDS (adapted from the New Oxford American Dictionary)
photocatalyst A substance that starts a chemical reaction when exposed to light.
chemical reaction A process that involves rearrangement of the molecules or structure of a substance, as opposed to a change in physical form.
titanium dioxide A white, unreactive, solid material that occurs naturally as a mineral and is used extensively as a white pigment.
silver iodide A yellow powder that darkens with exposure to light. It is used in photography and artificial rainmaking.