Thermal volatilisation analysis of a TDI-based flexible polyurethane foam containing ammonium polyphosphate

In this paper, we report a comprehensive study on a TDI-based foam containing 13% ammonium polyphosphate (APP) in order to examine the effect that this conventional fire retardant has on the thermal and thermo-oxidative degradation behaviour of the polyurethane foam. The results from TVA and TGA analyses show that the APP foam undergoes a significantly different degradation mechanism to the standard foam that we have reported on previously. The TGA results revealed the presence of a two-stage degradation process under a non-oxidative environment. The TVA results, on the other hand, revealed that degradation of the APP foam in fact occurs in four overlapping steps compared to the two-step process which occurs for the standard foam. The additional degradation steps observed for the APP foam are proposed to correspond to degradation of the fire retardant. Evolution of volatile material was also observed to occur at a lower temperature for the APP foam and it is proposed that the primary degradation of the urethane linkages via a depolycondensation reaction is acid-catalysed by the acidic hydroxyl groups which arise from degradation of APP. The sub-ambient differential distillation trace revealed that the nature and distribution of the volatiles evolved from the APP foam were profoundly different to the standard foam, which confirms that the secondary degradation is also altered in the presence of APP.