Thermal and Thermal-Oxidative Degradation of Polyurethane Foams Filled with Ammonium Phosphate

The mechanisms of degradation of rigid Polyurethane foams (PU) filled with Ammonium Phosphate (AP) as inorganic flame retardant, have been studied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) both in inert (N₂) and oxidizing (air) atmospheres.

TGA analyses have shown that the filler modifies the thermal and the thermaloxidative decomposition of the polymer, but the formation of much more stable thermal structures with respect of unfilled PU can be obtained only in an oxidizing atmosphere.

The phosphoric acid formed by the endothermic decomposition of AP, acts as a dehydrating catalyst of the polymeric substrate, leading towards the formation of thermally stable structures (char precursors).

The reduction in the smoke density of the AP filled foams can be attributed to the actions in the solid phase of the H₃PO₄ that produce a slower thermaloxidative degradation of the polymer decreasing the flammable volatile and potentially toxic products and also producing a protective layer on the surface of burning material.