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Coating Builds Fire ‘Armor’ on Foam

Monday, August 8, 2011

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Gram for gram, novel carbon nanofiber-filled coatings devised by researchers from the National Institute of Standards and Technology (NIST) and Texas A&M University have reportedly outperformed conventional flame retardants used in the polyurethane foam of upholstered furniture and mattresses by at least 160 percent and perhaps by as much as 1,130 percent.

The test results suggest that significant fire-safety advantages can be gained by coating polyurethane foam (PUF) with a club-sandwich-like arrangement of thin layers containing carbon nanofibers and polymers. The experimental coating seems to create the equivalent of a “fire-resistant armor” on the porous foam, says NIST researcher Rick Davis.

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The coating outperformed conventional flame retardants by 160 to 1,130 percent, researchers said.

The results are reported in “Development of layer-by-layer assembled carbon nanofiber-filled coatings to reduce polyurethane foam flammability” in the journal Polymer.
 
Deadly Furnishing Fires

Ignition of soft furnishings accounts for about five percent of residential fires, and the consequences are disproportionately high. These fires are responsible for a 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. A complementary rule to regulate the flammability of upholstered furniture has been proposed recently.

Several organizations, however, have challenged the health and safety of some flame retardants designed to protect against soft furnishing fires. And a bill pending in California would ban the use of certain halogenated flame retardants in that state.

Lightweight Coating

Today, recipes for making PUFs result in foams in which fire retardants are embedded in the interior.

In contrast, the NIST-Texas A&M experimental technology uses the carbon nanofiber fire retardant as a coating that covers all the nooks and crannies on the sponge-like PUF surface. This approach 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 coated square samples of commercially available PUF with four bilayers of a carbon nanofiber-polymer combination (polyethylenimine/carbon-nanofiber). The average thickness of the coating was about 360 nanometers, increasing the mass of the foam by only 3 percent. By themselves, the carbon nanofibers accounted for 1.6 percent of the foam mass. Because the carbon nanofibers are only in the coating, all the nanofibers are clumped like matted whiskers within the top 360 nanometers of the surface—assembled into the fire-blocking armor.

Flammability Testing

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. Reductions in flammability achieved with the coating, according to the researchers, were 158 percent better than the reduction calculated for non-halogens, 288 percent better than halogens, and 1,138 percent better than halogen-phosphorous flame retardants.

Additionally, the experimental coating “prevents the formation of a melt pool of burning foam, which in a real fire scenario, may further reduce the resulting fire threat of burning soft furnishings,” the authors write.