Characterization of Flame Retarded Polymer Combustion Chars by Solid-State 13C and 29Si NMR and EPR.
Characterization of Flame Retarded Polymer Combustion
Chars by Solid-State 13C and 29Si NMR and EPR.
(824 K)
Gilman, J. W.; Lomakin, S. M.; Kashiwagi, T.;
VanderHart, D. L.; Nagy, V.
Polymer Preprints, Vol. 38, No. 1, 802-803, April 1997
AND Fire and Materials, Vol. 22, No. 2, 61-67,
March/April 1998,
Keywords:
char; nuclear magnetic resonance; electron paramagnetic
resonance; radicals; char formation; polymers;
flammability
Abstract:
Additives that increase the amount of charcoal-like
residue of carbonaceous char that forms during polymer
combustion are very effective fire retardants. However,
very little is understood about the detailed structure
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 fed back 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 polymer processing temperature but below the
temperature where rapid gassification of the polymer to
combustible fuel occurs. We report here the 29Si, 13C
NMR and EPR analysis of polymer chars. We found that
the ratio of non-protonated carbon to protonated carbon
is ~ 1.5 + 01.1. It appears that the additives do not
change the type if char formed, but they do change the
rate of char formation relative to the rate of fuel
generation, since the char yield is higher and the
flammability (due to a lower fuel generation rate) is
reduced.
