Team Devises Better Flame Retardant for Polyurethane Foam

The NIST researchers may have achieved a breakthrough: a sustainable, nonhalogenated flame retardant to protect foam that is used in home furnishings.

The National Institute for Standards and Technology has reported a promising development that could yield a sustainable, nonhalogenated flame retardant for polyurethane foam -– sought because there is strong interest in developing better flame retardants for home furnishings. NIST said the researchers created a fast-forming coating that contains flame-inhibiting clay particles and adheres strongly to the foam.

Polyurethane foam is used in carpet padding, furniture cushions, and children's car seats, among other products.

"In effect, we can build the equivalent of a flame-retarding clay wall on the foam in a way that has no adverse impact on the foam manufacturing process," NIST fire researcher Rick Davis said in the agency's news release. "Our clay-based coatings perform at least as well as commercial retardant approaches, and we think there's room for improvement. We hope this new approach provides industry with practical alternative flame retardants."

"To date, researchers have built up coatings by stacking thin layers in pairs that are held together by basic electrical attraction. With no clay present, just a pure polymer, a thick coating is formed rapidly, but it isn't a fire retardant. With clay in every other layer, either the coating is too thin or the clay content is too low to be an effective fire retardant," the release explains. "The NIST team tried something you would expect not to work: trilayers consisting of a positively charged bottom topped by two negatively charged layers. Under most circumstances, the two negative layers would repulse each other, but it turns out that hydrogen bonds formed between the two negative layers and overcame this repulsive force. The resulting trilayer yields a unique result: a thick, fast-forming, and high concentration clay coating on polyurethane foam. This nanocomposite coating is 10 times thicker, contains 6 times more clay, and achieves this using at least 5 times fewer total layers than the traditional bilayer coatings."

The transparent coating produced is a few hundred nanometers thick. Foam treated with it retains its original softness, support, and feel, according to the researchers, who have published a paper explaining their process in the journal ACS Macro Letters.

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