EFFECT OF AMMONIUM POLYPHOSPHATE ON COMBUSTION AND THERMAL-DEGRADATION OF ALIPHATIC POLYAMIDES

Chain fragments with amide and imide groups are the most abundant degradation products of aliphatic polyamides (APA) which derive from scission of the N-alkylamide bond (-CH2-NH-). In the case of polyamide 6.6 (PA-6.6), also carbodiimide structures and methyl chain ends are formed, which derive from scission of -CH2-C(=O)- bond. Cyclic compounds can be formed besides chain fragments, depending on the type of APA. Ammonium polyphosphate (APP) reacts with APA on heating forming phosphoric esters which decompose giving products similar to those obtained from pure APA. APP increases the yield of carbodiimides from PA-6.6 which trimerise to triazine structures. The fire retardant mechanism of APP is discussed on the basis of the thermal degradation of the mixtures.