EFFECT OF THE FIRE-RETARDANT, AMMONIUM POLYPHOSPHATE, ON THE THERMAL-DECOMPOSITION OF ALIPHATIC POLYAMIDES .2. POLYAMIDE-6

The thermal degradation of polyamide 6 (PA-6) occurs through competing mechanisms leading to caprolactam, chain fragments with nitrile and carbon-carbon unsaturated chain ends and a small amount of residue stable to 550-degrees-C. A chemical interaction is shown to take place between ammonium polyphosphate (APP) and PA-6 on heating, resulting in destabilization of PA-6 and modification of its degradation behaviour. Caprolactam is the major volatile product obtained from the mixtures, whereas the yield of residue seems not to be affected. It is shown that the intumescent behaviour induced by APP in mixtures with PA-6 is responsible for its fire-retardant action.