Thermal degradation of polymer - fire retardant mixtures. Part II: Mechanism of interaction in polypropylene - chlorinated paraffin mixtures

The thermal degradation of polypropylene is accelerated when it is heated in mixtures with a fire retardant chlorinated paraffin (Cl 70%) whose dehydrochlorination rate is simultaneously reduced. The mechanism proposed to account for this behaviour involves the attack of the chlorine atoms, which propagate the dehydrochlorination reaction, on the tertiary hydrogen atoms of polypropylene with formation of HCl. The kinetic chain length of the dehydrochlorination is decreased and the rate of evolution of HCl is lowered, while the radicals formed on the polypropylene chain lead to its scission and volatilisation. The effects of these reactions on the fire retardant performance of the mixture are discussed.