Removing yellow stains from fabric with blue light

Summary

Exposing a sweat-like stain on cotton (left image) to a blue LED light for 10 minutes significantly removed the yellow color (right image). Credit: Tomohiro Sugahara Sweat and food stains can ruin your favorite clothes. But bleaching agents such as hydrogen peroxide or dry-cleaning solvents that remove stains aren't options for all fabrics, especially delicate ones. Now, researchers in ACS Sustainable Chemistry & Engineering report a simple way to remove yellow stains using a high-intensity blue LED light. They demonstrate the method's effectiveness at removing stains from orange juice, tomato juice and sweat-like substances on multiple fabrics, including silk. "Our method utilizes visible blue light in combination with ambient oxygen, which acts as the oxidizing agent to drive the photobleaching process," says Tomohiro Sugahara, the study's corresponding author. "This approach avoids the use of harsh chemical oxidants typically required in conventional bleaching methods, making it inherently more sustainable." Yellow clothing stains are caused by squalene and oleic acid from skin oils and sweat, as well as natural pigments like beta carotene and lycopene, present in oranges, tomatoes and other foods. UV light is a potential stain-removing alternative to chemical oxidizers like bleach and hydrogen peroxide, but it can damage delicate fabrics. Sugahara and Hisanari Yoneda previously determined that a high-intensity blue LED light could remove yellow color from aged resin polymers, and they wanted to see whether blue light could also break down yellow stains on fabric without causing damage. Initially, they exposed vials of beta-carotene, lycopene and squalene to high-intensity blue LED light for three hours. All the samples lost color, and spectroscopic analyses indicated that oxygen in the air helped the photobleaching process by breaking bonds to produce colorless compounds. Next, the team applied squalene onto cotton fabric swatches. After heating the swatches to ...