A group of Swiss scientists tested how well silver nanoparticles stayed in treated fabrics under conditions similar to a washing machine. They considered mechanical stress and chemical factors such as bleaches, pH and surfactants.
First, they measured the silver content of several different brands and types of fabrics that had silver nanoparticles either incorporated into or bound to the cotton, nylon or polyester fibers. They also included a fabric lined with a layer of silver that was not in the nanoparticle form.
They then washed the fabrics either once or twice in detergent. They added steel balls to simulate mechanical stress that would be similar to normal washing conditions. Some of the fabrics were also treated with bleaching agents during washing. These chemicals contribute the oxidants – the molecules that donate oxygen and therefore “bleach” the fabric.
Finally, the amounts and sizes of the particles of silver that came out of the fabrics were measured.
The silver content of the fabrics varied enormously, and several products had relatively low silver content.
A big difference was seen between the silver lined and the nanoparticle treated fabrics. The fabric lined with silver contained more than 600 milligrams (mg) of silver per ounce of fabric, about 7,200 times more silver than the nanoparticle fabric with the smallest silver content.
In comparison, the nanoparticle-impregnated fabric with the highest silver content had about 75 mg per ounce of fabric. Among the different nanoparticle-treated fabrics, the silver content ranged up to 130 times higher than the fabric with the lowest silver content.
When the fabrics were washed in water with detergent only, the silver generally stayed in the fabrics. However, several fabrics released silver quite readily once the steel balls were added to mimic mechanical actions of the washing machine. Of the 7 nanoparticle fabrics subjected to mechanical stress, four lost roughly 20 percent to 35 percent of their silver with the first wash. The amount released was always less with a second wash. Yet, one brand lost over half of its silver content from the fabric with just two washings.