Flame-retardant water-blown rigid polyurethane foams (RPUFs) modified by ammonium polyphosphate (APP) and diethyl ethylphosphonate (DEEP) were synthesized by a one-pot free-rising method. We performed scanning electron microscopy (SEM), compression strength tests, acoustic absorption measurements and thermogravimetric analysis, as well as limited oxygen index, vertical burning and cone calorimeter tests to investigate the mechanical properties, acoustic performance and flame retardancy of the foams. SEM confirmed that the open-cell structures of the foams were successfully constructed with the introduction of a cell-opening agent. Upon using 20 php APP, the average acoustic absorption coefficient of the foam reached 0.535 in an acoustic frequency range of 1500–5000 Hz. The results of thermogravimetric analysis demonstrated that the incorporation of APP and DEEP can effectively restrain mass loss of RPUFs during pyrolysis. In particular, the compressive strength of a foam composite containing 5 php APP and 15 php DEEP increased to 188.77 kPa and the LOI value reached 24.9%. In a vertical burning test and a cone calorimeter test, the joint use of APP and DEEP endowed RPUFs with a V-0 rating and they attained a THR value of 23.43 MJ/m2. Moreover, the addition of APP improved the acoustic absorption performance of the foam, verified by acoustic absorption measurements. Considering potential applications, the formulation containing 15 php APP and 5 php DEEP could be used in the preparation of a new flame-retardant acoustic absorption rigid polyurethane foam.

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 .