The pyrolysis behaviors of phosphorus-containing organosilicon compound modified ammonium polyphosphate with different phosphorus-containing groups, and their different flame-retardant mechanisms in polyurethane foam

· and PO· free radicals. Evaluation of the flame-retardant effect by means of the cone calorimeter test demonstrated that MAPP2 had better flame-retardant properties in the LD-RPUF system, including the reduction of peak heat release rate, total heat release, and total smoke release. Moreover, the char yield of LD-RPUF/MAPP2 was more than that of LD-RPUF/MAPP1. Macro and micro photographs showed that MAPP2 can promote the LD-RPUF matrix to form an intumescent char layer with more complete and stable foam during the combustion process compared with MAPP1. Finally, a possible flame-retardant mechanism of MAPP1 and MAPP2 in LD-RPUF is proposed.