Fire-Resistant Polymers May Improve Aircraft Safety

Research into new polymers targeted for aircraft safety shows that they are much more fire-resistant than current materials and, when heated, actually produce water vapor and leave a nearly nonflammable residue. The new findings are expected to help prevent some of the deaths in "survivable" airplane accidents, 40% of which are due to fires.

Polymer Research Program
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The polymer research was conducted at the University of Massachusetts (Amherst), and the Federal Aviation Administration, and is part of an ongoing series of studies into new fire-resistant polymers. The research is sponsored by a government and industry consortium created to improve aircraft safety.

Two new experimental techniques, requiring only milligrams of material, were developed by the researchers to measure the combustibility of the new polymer. Using the techniques to evaluate the polymer, known as polyhydroxyamide (PHA), they found it decomposed very little in contrast to other polymers. The PHA that did decompose was converted to water vapor and another nearly nonflammable polymer. "Quantum molecular modeling established how the decomposition gave water and a different type of solid polymer, polybenzoxazole (PBO), that is extremely fire-resistant," says University of Massachusetts Professor Phillip Westmoreland, lead author of the study.

So, why not just start with PBO instead of PHA? "You can't start with PBO because it is too hard to make into useful products, such as fabrics or panels," Westmoreland says. "PHA is a 'smart' fire-safe material. It can be made and processed by mild 'green chemistry' processes, yet when subjected to fire dangers, it converts into strong, stable PBO."

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"If you look around in an aircraft, most of what you see is not metal, it's polymeric—the walls, the bins, the seats, the windows, just about everything except the chair supports," Westmoreland says. Although polymers don't actually burn, Westmoreland points out, they decompose from heat and many of them produce gases that burn.

"Forty percent of fatalities in impact-survivable accidents are due to fire," adds co-researcher Richard Lyon, FAA program manager for fire research and fire safety in Atlantic City, NJ, referring to statistics for large transport aircraft operated by U.S. carriers. About half of the total deaths in passenger airline accidents, according to the FAA, occur in non-survivable crashes, such as might happen when a plane hits a mountain. The other 50% of the deaths occur in what are generally considered impact-survivable accidents, such as runway collisions causing spilled fuel to ignite.

PHA has potential applications beyond aircraft, according to Westmoreland. "The Army Materiel Division in Natick, MA, has a crash three-year program to come up with more fire-safe clothing for military uniforms," he says. The new testing techniques also are useful for other new materials, he says, because it makes it possible to test very small samples efficiently, thereby reducing the need to spend time and money producing large amounts of the new material for analysis.

The key to this study's success, Westmoreland points out, is the integrated approach of polymer synthesis, flammability testing, and molecular modeling.

The research was reported at the national meeting of the American Chemical Society (Anaheim, CA; March 23, 1999).

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