AMHERST, Mass. - Researchers at the University of Massachusetts have developed polymers that could make air travel safer. Phillip Westmoreland, professor of chemical engineering at UMass, presented the group''s findings at the March 1999 national meeting of the American Chemical Society. The research is being conducted in conjunction with the Federal Aviation Administration (FAA).
Polymers are extremely long chains of molecules which can be custom-made to offer certain characteristics. The new PHA polymers, (polyhydroxyamides), are more fire-resistant than materials currently used in commercial airliners. In a fire, they break down to a nearly nonflammable residue and a small amount of water vapor.
"If you look around an aircraft, most of what you see is not metal, it''s polymeric," said Westmoreland. "The walls, the overhead bins, the seats, the windows, just about everything except the chair supports are made of polymers."
"We shouldn''t lose sight of the fact that airline travel is very safe," said Constantine Sarkos, FAA manager of fire safety. "In 1998 there were no fatal accidents in U.S. carrier operations. Historically, the chances of being in a fatal accident are about two million to one." Advances have been made in recent years to make the interiors of planes more fire-safe, using smoke detectors, floor-level guidance lights, and safer polymers. In an effort to reduce fire dangers even more, polymer fire-resistance has become a key target, according to Westmoreland.
Polymers are important in aviation, because of their lightness, strength, and versatility, said Westmoreland. They can be produced in many forms and shapes, including fibers that can be used as fabric on seats, and that can be dyed or imprinted. However, like many construction materials, these fibers are also flammable. "In a narrow sense, polymers don''t actually burn," Westmoreland said. "They decompose from heat, generating gases that burn. Heat from the flame then causes further decomposition and more flammable gases."
These gases can be sparked into a "flashover" - a catastrophic fire in the aircraft cabin. Such fires, experts say, are nearly impossible to survive. If a flashover can be delayed by 10 to 15 minutes, passengers may have time to escape from the airplane, even allowing for blocked exits, according to Richard Lyon, head of the FAA fire research program and a UMass alumnus. That time could also allow emergency crews to rescue passengers who might be unconscious or unable to move due to their injuries, he added.
About half of the total deaths in passenger airline accidents occur in non-survivable crashes, according to the FAA. However, the other 50 percent of deaths ocur following impact- survivable aircraft crashes, and about half of those are due to fire-related injuries, including smoke inhalation, Lyon said. The FAA''s goal is to eliminate burning cabin materials as a cause of death in aircraft accidents over the next 10 to 15 years, he said.
The UMass group identified a class of polymers called PHAs as strong candidates for fire-resistance. PHAs offer the strength, flexibility, and lightweight attributes of materials currently used, but when heated to 400 degrees Fahrenheit, they transform to a hard polymer called PBO (polybenzoxazole), which is highly stable. The reaction forms water molecules. "PHA is a ''fire-smart'' material. It can be made and processed by mild ''green chemistry'' processes, yet when subjected to fire dangers, it converts into stable PBO," said Westmoreland. Airline manufacturers can''t begin with PBO, he explained, because it is too difficult to form into useful products, such as fabrics or panels.
The UMass effort to design fire-safe polymers is multi-disciplinary, drawing on faculty members from both chemical engineering and polymer science and engineering. With graduate students Karin Rotem and Taline Inguilizian, Westmoreland identified polymer features that favored low flammability. Simon Kantor and postdoctoral associate Chunping Gao of polymer science and engineering then applied these insights to identify and make new materials in the laboratory. Meanwhile, the FAA''s Lyon and Westmoreland''s group each developed new experiments that made it possible to identify low flammability from small initial amounts of polymer. Finally, Westmoreland''s group used molecular modeling to establish decomposition reactions of the polymer, showing its range of use.
The research has been conducted under the auspices of the Center for UMass-Industry Research on Polymers. Its industrial members are examining the possibility of making the polymer commercially. Meanwhile, Richard Farris, head of the department of polymer science and engineering, and Kantor, along with their research teams, are studying other PHAs and their blends in an effort to produce even better polymers.