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Nanotech Coating Helps Reduce Flames in Polyurethane Foam

House fire (A. Kotok)

(A. Kotok)

Researchers from National Institute of Standards and Technology (NIST) and Texas A&M University in College Station have developed carbon nanofiber-filled coatings that outperform conventional flame retardants used in the polyurethane foam found in upholstered furniture and mattresses. Their findings appear in a recent issue of the journal Polymer (paid subscription required).

Ignition of soft furnishings account for about five percent of residential fires, and are responsible for one-third of fire-caused deaths of civilians and 11 percent of property losses due to fires in homes. The flammability of mattresses is regulated by federal law, with a similar rule to regulate the flammability of upholstered furniture currently under consideration.

The health and safety of some flame retardants designed to protect against soft furnishing fires, have come under scrutiny. A bill pending in California would ban the use of certain halogenated — compounds containing chlorine or bromine bonded to carbon — flame retardants in that state. And the Stockholm Convention on Persistent Organic Pollutants has banned 21 chemicals, all of which are halogenated.

The NIST-A&M team took a different approach to flame retardation. With current technologies, the chemicals are added to the recipe of the polyurethane foam (PUF) material. In contrast, the tested technology applied a carbon nanofiber fire retardant as a coating that covers all the bumps and indentations on the sponge-like foam surface.

Using a standard bench-top test to measure the fire performance of coated and uncoated PUF. The carbon nanofiber coatings reduced PUF flammability — measured as the peak heat release rate from an ignited specimen — by 40 percent. That result was more than three times better than achieved by using the current approach: putting the same carbon nanofibers in the foam itself as part of the foam recipe.

When compared at the same concentrations, the carbon nanofiber coating outperforms three classes of commercially available flame retardants commonly used in PUF. Reductions in flammability achieved with the coating, according to the researchers, were 158 percent better than the reduction calculated for nonhalogens, 288 percent better than halogens, and 1,138 percent better than halogen-phosphorous flame retardants.

The coating consisted of four thin layers containing carbon nanofibers and polymers sandwiched together. The average thickness of the coating was about 360 nanometers — one nanometer equals one billionth of a meter — increasing the mass of the foam by only 3 percent. By themselves, the carbon nanofibers accounted for 1.6 percent of the foam mass.

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