Polymer Combustion and Flammability-role of the Condensed Phase*

The combustion process of polymers is a complex coupling of energy feedback from a flame to the polymer surface with gasification of the polymer to generate combustible degradation products. Although there are extensive studies of the effects of wind velocity, gas phase oxygen concentration, external thermal radiation, and gravity on the combustion of polymers, the effects of polyruer characteristics on combustion and flammability are not nearly as well understood as those in the gas phase. At present, detailed governing equations for continuity, momentum, energy, and chemical species concentration in the gas phase can readily be written with appropriate boundary conditions, and their solutions can be derived for various cases. However, even those governing equations cannot be derived for the condensed phase without understanding of the governing chemical and physicat processes that control the gasification of polyruers. This paper concentrates on describing various observed phenomena in polymers (which have been often iguored or neglected) during their combustion, some or all of which might have significant effects on the burning rate and flammability properties. Because of a lack of understanding of the basic combustion mechanisms of polymers, theoretical models able to predict combustion phenomena aud flammability properties are not available, In order to overcome this problem, global material characteristics are currently measured by well-defined test methods, and the results are used as inputs to fire growth models intended to predict behavior of the materials in specific fire scenarios. To improve the fire performance of polymers, a nonhafogenated char-forming flame-retardant approach is suggested, and its benefits are discussed.