Firefighters are set to save a fortune on laundry bills. Researchers have come up with a coating for cotton fabric that is both flame-retardant and water-repellent, making it self-cleaning.
Fabrics with flame-retardant coatings are firefighter chic, but they are also used for curtains and furniture upholstery. The problem is that these coatings are water soluble, so can be worn away by washing.
"Fire disaster is one of the leading unintentional causes of injury, death and property loss in the world. With rational use of fire-retardant materials, a large number of injuries and deaths can be avoided," says Junqi Sun of Jilin University in Changchun, China. "However, it is a common problem for flame-retardants to wash away from flame-retardant materials such as fabrics, preventing their long-term applications."
Now Sun and his colleagues say they have the answer. Water-repellent coatings, known as superhydrophobic because droplets roll right off them, already exist. Why not combine the two into a single material capable of standing up to both fire and water? The rolling droplets carry dust and grime with them, so these coatings are self-cleaning as well.
Burning issue
The team took ordinary cotton and soaked it in a solution of a polymer called polyethylenimine, which acts as a binding agent, then in a solution of ammonium polyphosphate, a common flame retardant. Finally, they dipped the fabric in a mix of ethanol and a silsesquioxane, a cage-like molecule that has shown promise as a water repeller.
The result was a fabric that refuses to catch fire and is easily cleaned. The team placed a strip of uncoated cotton over a naked flame and it burned up completely in just 14 seconds. When they did the same with the coated fabric, it charred slightly and was extinguished as soon as the flame was removed.
Unfortunately, the charring is the result of chemical changes in the flame-retardant coating, so it won't wash off once it has been burnt. But the superhydrophobic layer means that, unlike other flame-retardant coatings, the fabric will offer full protection against fire after it has been washed.
Journal reference: ACS Nano, DOI: 10.1021/acsnano.5b00121
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