Synergistic flame retardancy and mechanical enhancement of flexible polyurethane foams by P/N/Zn complex-functionalized graphene nanohybrids: An integrated experimental and FDS simulation study

The flammability of flexible polyurethane foam (FPUF) and the degradation of mechanical properties caused by traditional flame retardants limit its application in scenarios with high safety requirements. To address this, a P/N/Zn complex-functionalized graphene (PPZ@fGO) nanohybrid was synthesized and incorporated into the FPUF matrix. Structural characterization confirmed its successful synthesis and uniform dispersion. Adding 5% PPZ@fGO increased the mechanical strength to 15.17 kPa, a 400.67% improvement over the control FPUF. This enhancement is attributed to synergistic physical entanglement and chemical crosslinking between PPZ@fGO and the matrix. Concurrently, the composites exhibited significant reductions in peak heat release rate (PHRR, 31.6%), total heat release (THR, 28.7%), and total smoke production (TSP, 30.3%) compared to control FPUF. The fire growth rate index (FIGRA) was lowered by 42.3%, with thermogravimetric analysis revealing a higher char residue (11.9%). This was due to the catalytic carbon formation of metal ions, expansion charring of PPZ, the barrier effect of fGO, and the dilution effect of nonflammable gases. Furthermore, a standard room fire model based on Fire Dynamics Simulator (FDS) was constructed to investigate its practical application in real-world scenarios. Simulation results revealed that the modified foam effectively suppresses rapid fire spread and severe thermal escalation. Specifically, the peak ceiling temperature dropped by 600–700 °C, and the steady-state carbon monoxide (CO) concentration was reduced by nearly 50% within 600 s, substantially prolonging the available safe egress time. This work provides a solution for developing FPUF with outstanding flame retardancy, smoke suppression properties, and mechanical strength.