EFFECT OF INTUMESCENCE ON POLYMER DEGRADATION

In the area of polymer flame retardancy, intumescent formulations offe r an attractive alternative to mineral and halogenated components. Pol ymer protection by formation of an intumescent layer during a conflagr ation is a complex phenomenon involving both chemical and physical pro cesses. This paper reports a comparative study of a number of intumesc ent systems for commercial ethylene-vinyl acetate polymers and based o n ammonium polyphosphate and polyol. It is shown that intumescent shie ld formation involves the presence of a stable phosphocarbonaceous str ucture. The efficiency of such protection has been assessed. Temperatu re profiles have been studied during the combustion of these materials in the LOI apparatus. The temperature-time profiles obtained show a p lateau region indicating heat transfer limitation within the intumesce nt coating. Moreover, cone calorimeter studies show that the maximum r ate of heat release from these intumescent coatings is four times less than that for the virgin polymer samples. Several models have been se t up and used to analyse the heat transfer phenomena observed during t he degradation of the various polymer systems under fire conditions.