Aging effects on fire-retardant additives in polymers

Extensive thermal aging experiments have been conducted on (i) ethylene-propylene rubber (EPR) formulations containing various commercial halogenated-hydrocarbon fire-retardant additives together with Sb₂O₃, and (ii) on chlorosulfonated polyethylene (CSPE) formulations with and without added Sb₂O₃. Significant losses of both chlorine and antimony are found on aging, dependent upon the ability of the particular halocarbon to undergo intramolecular dehydrohalogenation. The stoichiometry indicates antimony volatilization as SbCl₃. Arrhenius treatment of the data for the EPR formulation which undergoes the most rapid loss gives an overall activation energy of 34 kcal/mol for antimony volatilization and indicates that fire-retardant loss should become appreciable only at temperatures significantly above ambient (i.e., 70°C). Oxygen index flammability measurements showed moderately increased flammability for certain aged EPR samples, but showed significantly decreased flammability for aged CSPE which was correlated with the loss of other volatile components from the formulation.