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Char Enhancing Approaches to Polymer Flammability: The Effect of Radicals on Magic Angle Spinning 13C NMR of Chars.


pdf icon Char Enhancing Approaches to Polymer Flammability: The Effect of Radicals on Magic Angle Spinning 13C NMR of Chars. (213 K)
Gilman, J. W.; Lomakin, S. M.; Kashiwagi, T.; VanderHart, D. L.; Nagy, V.

NISTIR 5904; October 1996.

National Institute of Standards and Technology. Annual Conference on Fire Research: Book of Abstracts. October 28-31, 1996, Gaithersburg, MD, 133-134 pp, 1996.

Available from:

National Technical Information Service
Order number: PB97-153514

Keywords:

fire research; fire science; char; flammability; char formation; additives; thermal conductivity; radicals

Abstract:

Additives that increase the amount of charcoal-like residue or carbonaceous char that forms during polymer combustion are very effective fire retardants. However, very little is understood about the detailed struture of char or how it forms. Our research efforts focus on reducing polymer flammability by promoting char formation. Char formation reduces the amount of small volatile polymer pyrolysis fragments, or fuel, available for burning in the gas phase; this in turn reduces the amount of heat released and feedback to the polymer surface. The char also insulates the underlying polymer, due to its low thermal conductivity, and reradiates externally impinging energy away from the polymer. The char must also function as a mass transport barrier, by physically delaying the volatilization of decomposition products and or trapping decomposition products through chemical reaction. The physical structure of the char is important in this role. Foamy char structure appears to be more fire resistant than brittle, thin char. This char enhancing approach is most successful when the polymer chars rapidly and early in the burning process. To be useful the charring process must occur at a temperature above the processing temperature but below the temperature where rapid gasification of the polymer to combustible fuel occurs.