Abstract: Flame retardant flexible polyurethane foam (FPUF) were prepared by one-step foaming with ammonium polyphosphate (APP) and molybdenum trioxide (MoO3) as flame retardants. The effects of MoO3 and APP on the cellular structure,thermal stability, flame retardancy and smoke production of polyurethane foam were studied by means of scanning electron microscopy, limiting oxygen index, thermogravimetric analyzer and cone calorimeter. The results show that MoO3 and APP can improve the flame retardant performance of flexible polyurethane foam. Compared with pure flexible polyurethane foam, when the addition of APP and MoO3 is 7.5%, the total heat release and total smoke production of flame retardant flexible polyurethane foam are reduced by 44.2% and 66.3% respectively, showing better flame retardant and smoke suppression performance; The flame retardant mechanism of APP and MoO3 flame retardant flexible polyurethane foam is discussed. APP plays a flame retardant role in the gas phase and condensed phase. Free radicals in the gas phase are captured by generating phosphorus containing functional groups in the gas phase. The condensed phase plays a role in catalytic carbonization. MoO3 promotes the catalytic carbonization of pyrolysis polyurethane, improves the carbonization rate, compacts the carbon layer, and improves the thermal stability of flexible polyurethane foam. The fire safety of flexible polyurethane foam is effectively improved.

Key words: flexible polyurethane foam, MoO3, ammonium polyphosphate, flame retardant performance, smoke suppression, thermal stability