Char Enhancing Approaches to Polymer Flammability: The Effect of Radicals on Magic Angle Spinning 13C NMR of Chars.
Char Enhancing Approaches to Polymer Flammability: The
Effect of Radicals on Magic Angle Spinning 13C NMR of
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
fire research; fire science; char; flammability; char
formation; additives; thermal conductivity; radicals
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