Fire retardant systems based on melamine hydrobromide. Part 1: Fire retardant behaviour

The fire retardant characteristics of additives based on mixtures of melamine hydrobromide-free radical initiator-basic bismuth carbonate (or antimony trioxide) are discussed on the basis of the dependence of oxygen index on composition in the case of polypropylene. It is shown that the free radical initiator enhances the effectiveness of the fire retardant action of melamine hydrobromide. A further significant decrease of flammability, as measured by oxygen index, is induced by addition of the metal compound. Thus, polypropylene can be fire retarded with very small amounts of additive (<2%) without excessive formation of smoke which is typical of the most common halogenated additives. This seems to be due to a smoke suppressant activity of the melamine structure. These additives act by a condensed phase mechanism which seems not to be limited to induction of extensive dripping of the polymer on burning.