Char Enhancing Approaches to Flame Retarding Polymers.
Char Enhancing Approaches to Flame Retarding Polymers.
(1278 K)
Gilman, J. W.; Kashiwagi, T.; Harris, R. H., Jr.;
Lomakin, S. M.; Lichtenhan, J. D.; Bolf, A.; Jones, P.
Chemistry and Technology of Polymer Additives. Chapter
8. 1999, Blackwell Science Inc., Malden, MA,
Ak-Malaika, S.; Golovoy, A.; Wilkie, C. A.,
Editor(s)(s), 135-150 pp, 1999.
Keywords:
char; flame retardants; additives; silica gel;
flammability; cone calorimeters; heat release rate;
zirconium oxide; preceramics
Abstract:
Additives that increase the amount of charcoal-like
residue or carbonaceous char that forms during polymer
combustion are very effective fire retardants (FR). Our
research efforts focus on reducing polymer flammability
by promoting char formation. Our approach to char
promotion is to investigate additives which enhance
charring, and to gain a fundamental understanding of the
additives' mechanism of char formation with the goal of
optimizing their performance. 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 incident energy away from
the polymer surface. The char must also function as a
mass transport barrier, by physically delaying the
volatilization of decomposition products and/or
chemically reacting with decomposition products. The
physical structure of the char is important in this
role. Thick, foamy char 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 gasification of the polymer to
combustible fuel occurs. This chapter is an overview of
several new char enhancing approaches to reducing the
flammability of polymers.
