Rigid polyurethane foam compounds with excellent fire performance modified by a piperazine pyrophosphate/expandable graphite synergistic system

Rigid polyurethane foam (RPUF) has many excellent properties, but its flammability has been a challenge for the application of RPUF compounds. In this research, piperazine pyrophosphate (PAPP) and expandable graphite (EG) were added to the RPUF matrix to improve the fire performance of RPUF. Thermogravimetric analysis (TGA) revealed that PAPP and EG contributed to the early decomposition of the FR-RPUF matrix, and the char residue of RPUF-3 reached 37.1 wt% when the PAPP: EG ratio was 1:1. The flame-retardant test indicated that the FR-RPUF composites reached the V-0 level, and the limiting oxygen index (LOI) value of RPUF-4 was 28.8%. In addition, cone calorimeter tests showed that the addition of flame retardants reduced the peak heat release rate (PHRR) and total heat release (THR), further improving the fire performance of the compounds. The analysis of the char residue confirmed the formation of a denser char residue and significant improvement in the graphitization degree due to the PAPP/EG synergistic effect, indicating that the char residue could effectively isolate oxygen and heat and act as a flame retardant in the condensed phase.