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 s tudied using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) both in inert (N2) and oxidizing (air) atmospheres. TG A analyses have shown that the filler modifies the thermal and the the rmal-oxidative decomposition of the polymer, but the formation of much more stable thermal structures with respect of unfilled PU can be obt ained only in an oxidizing atmosphere. The phosphoric acid formed by t he endothermic decomposition of AP, acts as a dehydrating catalyst of the polymeric substrate, leading towards the formation of thermally st able structures (char precursors). The reduction in the smoke density of the AP filled foams can be attributed to the actions in the solid p hase of the HPO4 that produce a slower thermal-oxidative degradation o f the polymer decreasing the flammable volatile and potentially toxic products and also producing a protective layer on the surface of burni ng material.