NIST Finds Nanofiber Coatings Prove Effective as Fire Retardant
Researchers from the National Institute of Standards and Technology (NIST) and Texas A&M University have developed a carbon nanofiber-filled coating that can outperform today’s flame retardants used with polyurethane foam, a common material for upholstered furniture and mattresses.
Test results suggest that nanomaterial could provide significant fire-safety advantages against ignition of soft furnishings, which account for about 5 percent of residential fires, and as many as one-third of all civilian fire-caused deaths, the researchers said.
The NIST-Texas A&M team coated square samples of commercially available PUF with four bi-layers of a carbon nanofiber-polymer combination, creating what Davis called a ‘club-sandwich’ layering effect. The average thickness of the coating was about 360 nanometers, increasing the mass of the foam by only 3 percent. Because all the carbon nanofibers are clumped at the top layer (360 nms) like matted whiskers, the approach results in the nanomaterials assembling into the fire-blocking armor.
The carbon nanofibers accounted for 1.6 percent of the foam mass. Since the carbon nanofibers are only in the coating.
Today, recipes for making PUFs result in foams in which fire retardants are embedded in the interior. In contrast, the experimental technology uses the carbon nanofiber fire retardant as a coating that covers all the nooks and crannies on the sponge-like PUF surface. The new approach, says Davis, should be attractive to PUF manufacturers because the surface treatment has the potential to deliver a low flammability PUF without major change to the foam manufacturing process, thus saving time and money.
The team used a standard benchtop fire 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 3 times better than achieved by putting the same carbon nanofibers in the foam (part of the foam recipe).
When compared at the same concentrations, the carbon nanofiber coating significantly outperforms three classes of commercially available flame retardants commonly used in PUF -- nonhalogens, halogens, and halogen-phosphorous flame retardants.
The nanocoating also "prevents the formation of a melt pool of burning foam,,” according to the team.
The research comes as several organizations are challenging the health and safety of current flame retardants, and as a bill to ban some halogenated flame retardants is under consideration in California.
The work is published in the journal Polymer (Vol. 52, Issue 13, June 8, 2011) Y.S. Kim, R. Davis, A.A. Cain and J.C. Grunlan, Development of layer-by-layer assembled carbon nanofiber-filled coatings to reduce polyurethane foam flammability.