Effect of expandable graphite and molybdenum trioxide in nitrogen/phosphorus synergistic system on acoustic performance and fire safety in rigid polyurethane foam

Abstract To explore acoustic performance and flame retardancy of expandable graphite (EG) and molybdenum trioxide (MoO 3 ) in rigid polyurethane foam (RPUF) with nitrogen/phosphorus synergistic system, ammonium polyphosphate (APP), diethyl ethylphosphonate (DEEP), EG, and MoO 3 were employed in RPUF. Compared with flame‐retarded RPUFs, neat‐RPUF attained an open porosity value of 45.3%, which provided good tortuosity for wave propagation and acoustic attenuation, and therefore had the best performance in acoustic absorption. Although the addition of flame retardant sacrificed sound‐absorbing properties, the flame retardancy performance of foams were indeed significantly improved. The Limited Oxygen Index (LOI) value of RPUF with 70 php EG alone increased from 19.4% of Neat‐RPUF to 35.6%. Regarding to CO and CO 2 emission, RPUF with 10 php MoO3, 30 php APP, and 30 php DEEP gained minimum value of average CO yield and average CO 2 yield, which were 0.06 kg/kg and 0.78 kg/kg, respectively, ascribed to the accelerated formation of the compact carbon layers by MoO 3 .