Green fire retardant swells to suppress flames

Laura Howes/Denver, US

Jamie Grunlan’s team at the University of Texas A&M, US, has used layer by layer deposition to coat fabrics with a thin, environmentally benign, fire retardant layer of polymers. The polymer coating reacts to fire and swells up to form a foam, protecting the fabric and killing the fire.

’1 per cent of GDP is lost through fire each year,’ Grunlan says, ’but much of the current [fire retardant] technology is toxic and being outlawed by various countries.’ Grunlan has been working on various less toxic alternatives.

’Many flame retardants are coming under the environmental spotlight because of their ecotoxicity,’ says Richard Hull, professor of chemistry and fire science at the University of Lancashire, UK. ’Brominated flame retardants are probably the worst.’ Currently, brominated fire retardants are used to fireproof fabrics, so Grunlan decided to look for a replacement.

To protect a small piece of cotton, Grunlan immerses the fabric in a dilute aqueous solution of poly(sodium phosphate), rings it out and then puts the fabric in a weak solution of poly(allylamine). Repeating the process gives the cotton a thin coating of alternating polymers 10s to 100s of nanometres thick. When a flame hits the polymers, it initiates an acid-base reaction that releases water vapour and this puffs up the polymer into a foam.

Tumescent coatings - materials that expand into a foam upon contact with high heat or a flame - haven’t been used on fabrics before, says Grunlan, but they are often used as thicker coatings in buildings.

The cotton coating doesn’t degrade or weaken the material says Grunlan. The technology does have one drawback though, as the coating makes the cotton slightly less flexible, more like canvas. But Grunlan says he’s already working on more flexible polymers, as well as making sure the coating survives multiple washes.

Grunlan has a patent pending on the work and says he is now looking for a commercial partner to help him develop the technology. When he finds one, he says he sees no reason why this coating couldn’t be on the market within a year.