Not to sound like a TV commercial or anything, but … how often have you had to throw out white shirts because of unsightly yellow underarm stains? Well, those stains may not be a problem any longer, thanks to a simple blue light treatment.
Yellow armpit stains in white clothing are typically caused by oleic acid and an organic compound known as squalene, which are found in our sweat and skin oils. Stubborn yellow stains can also be caused by natural pigments such as lycopene and beta carotene, which make their onto our clothing in spilled beverages like tomato and orange juice.
Both bleach and ultraviolet light exposure are effective at removing such stains, but unfortunately they're also hard on delicate fabrics. With that drawback in mind, two scientists from Japan's Asahi Kasei Corporation looked to high-intensity blue LED light.
In a previous study, Tomohiro Sugahara and Hisanari Yoneda found that such light was effective at removing yellow discoloration from aged resin polymers.
For the new study, the researchers started by exposing vials of beta-carotene, lycopene and squalene to the blue light for three hours. All of the samples lost color due to a blue-light-boosted photobleaching process, in which oxygen in the air broke chemical bonds within the substances, converting them into colorless compounds.
The scientists then went on to apply squalene to white cotton swatches – thus staining them – after which they heated those swatches to simulate aging, then treated them for 10 minutes via either blue LED light exposure, UV light exposure, or a soak in a hydrogen peroxide solution.
It was found that the blue light was most effective at removing yellow squalene stains, without damaging the fabric. Further testing showed that the treatment also worked on stained polyester and silk swatches without harming them. More research is now being conducted, with an eye towards ultimately developing home-use and industrial stain removal systems.
"Our method utilizes visible blue light in combination with ambient oxygen, which acts as the oxidizing agent to drive the photobleaching process," says Sugahara. "This approach avoids the use of harsh chemical oxidants typically required in conventional bleaching methods, making it inherently more sustainable."
A paper on the study was recently published in the journal ACS Sustainable Chemistry & Engineering. And the potential uses of high-intensity blue LED light don't stop at stain removal – other studies are exploring its antibacterial effect.
Source: American Chemical Society
