Fire retardant systems based on melamine hydrobromide. Part 2: Overall thermal degradation

The thermal degradation is studied of the mixture, melamine hydrobromide-free radical initiator-basic bismuth carbonate which is a very effective fire retardant for polypropylene. Melamine hydrobromide condenses on heating, evolving ammonia and ammonium bromide. The melamine condensate then undergoes complete volatilisation above 540°C with evolution of nitrogen-containing species. Addition of the free radical initiator does not appreciably affect the thermal degradation behaviour of melamine hydrobromide. Further addition of basic bismuth carbonate strongly modifies the volatilisation of nitrogen-containing species and leads to evolution of bismuth tribromide. On addition to polypropylene, the thermal degradation of the ternary mixture is further modified with formation of metallic bismuth. Implications of thermal degradation behaviour on fire retardance mechanism are discussed.