Layers of polymers can help make environmentally-friendly flame retardant coatings.
Flame retardants have been under fire in recent years because of their potentially toxic effects. So, researchers are developing alternative materials with more health- and environmentally-friendly chemical composition. Several reporters wrote about a new layered polymer technology created by a team led by Jaime Grunlan at Texas A&M University in College Station.
Janet Raloff at Science News reports:
Materials scientists in Texas have developed flexible coatings mere billionths of a meter thick that keep cotton clothing from going up in flames and plastic foam from melting. Unlike the widely used but potentially toxic flame retardants they’ve been designed to replace, these nano-coatings appear relatively safe, their designers say.
One technology was described at the American Chemical Society meeting in Denver last week, and the other in the journal Advanced Materials earlier this summer.
Laura Howe writes in Chemistry World about the coating that works by protecting individual fabric fibers:
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,” Grunlan told Howe, “but they are often used as thicker coatings in buildings.”
Lauren Wolfe at Chemical & Engineering News gives details about the coating that the team shows protects foam material. The material is:
[...] composed of alternating nanolayers of montmorillonite, or clay, and chitosan, a linear polysaccharide. During 10 seconds of exposure to a butane torch, polyurethane foam coated with 10 bilayers of the clay-chitosan film escaped with only a blackened skin.
Despite its charred outer layer, Grunlan says, the foam’s white, squishy innards remain intact.
Charles Wilkie, a flame retardant expert at Marquette University who is not involved with the work, told reporters that he was impressed by the new technology. However, he told Raloff, “in the real world, fires last considerably longer than 10 seconds… so these materials might retard burning or limit its spread, but wouldn’t withstand an inferno.”
Despite numerous positive comments about the work, whether the multiple-dip process would be commercially cost-feasible remains to be seen.
Grunlan said in a press release that the team is looking into finding a commercial partner and ways to make the polymer coatings even more flexible and able to withstand multiple washings.
Source: “Fighting flames with greener materials,” Science News, 8/31/11
Source: “Green fire retardant swells to suppress flames,” Chemistry World, 9/1/11
Source: “Making Greener Flame Retardants,” Chemical & Engineering News, 8/31/11
Source: “Intumescent All-Polymer Multilayer Nanocoating Capable of Extinguishing Flame on Fabric,” Advanced Materials, 7/29/11
Source: “A ‘nano,’ environmentally friendly, and low toxicity flame retardant protects fabric,” Americal Chemical Society press release, 8/31/11
Image by mathewvenn, used under its Creative Commons license.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.
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