Inorganic/organic phosphorus‐based flame retardants synergistic flame retardant rigid polyurethane foam

Abstract The flame‐retardant rigid polyurethane foam (RPUF) composites are fabricated by ammonium polyphosphate (APP) with pentaerythritol phosphate (PEPA), phenoxycycloposphazene (PCP), and aluminum diethylphosphinate (ADP), respectively, which are labeled as RPUF‐1, RPUF‐2, and RPUF‐3. The influence of flame retardants on the apparent density and compressive strength of RPUF is studied. The results reveal that flame retardants not only improve the apparent density, but also improve the compressive strength of RPUF composites. The limiting oxygen index (LOI) results reveal that these inorganic/organic phosphorus‐based flame retardants improve the LOI significantly, especially for RPUF‐2 and RPUF‐3 systems. The cone calorimeter test results suggest that the peak of heat release of RPUF‐1, RPUF‐2, and RPUF‐3 systems decrease by 38%, 41%, and 52% likened to that of pure RPUF. And APP and ADP system performs best in declining the heat release. And APP and PEPA systems perform best in decreasing the smoke release. The flame retardancy mechanism of RPUF composites is analyzed in details.