Flame retardancy and smoke suppression of reused flexible polyurethane foam: Synergistic effect of hydrophobic silica aerogel and organophosphorus flame retardant by Kabachnik-Fields reaction

A flexible polyurethane foam (FPF) composite with enhanced flame retardancy and smoke suppression was developed by incorporating hydrophobic silica aerogel (SA) and a P–N–aryl structured organophosphorus flame retardant (P-FR) synthesized via the Kabachnik–Fields reaction. Reused waste FPF was employed as the matrix, providing a sustainable and scalable route for upgrading discarded polyurethane foams into multifunctional insulation materials via ambient-pressure aerogel processing. Cone calorimeter tests demonstrated a pronounced improvement in fire performance. Incorporation of SA significantly suppressed heat release, reducing the peak heat release rate (pHRR) from 298.2 kW/m 2 for neat FPF to 91.3 kW/m 2 and decreasing the maximum average rate of heat emission (MARHE) from 162.4 to 57.0 kW/m 2 . Further addition of only 5 phr P-FR led to additional reductions in pHRR (84.8 kW/m 2 ) and MARHE (52.1 kW/m 2 ), indicating a synergistic effect beyond the aerogel barrier mechanism alone. The synergy between SA and P-FR was particularly evident in smoke suppression behavior. Total smoke production was reduced from 4.96 m 2 for neat FPF to 2.37 m 2 for FPF/SA and further to 1.22 m 2 for FPF/SA/P-FR, corresponding to an overall reduction of 75.3%. In contrast, the mean effective heat of combustion decreased only modestly, from 27.29 to 23.45 MJ/kg, suggesting that fire hazard reduction primarily arises from controlled heat release dynamics and stabilized condensed-phase char formation rather than a fundamental change in fuel calorific value. Overall, this study demonstrates that silica aerogels can extend beyond conventional thermal insulation to play a key role in advanced fire-protective systems by nano-channel. The combined SA/P-FR strategy enables simultaneous suppression of heat release and smoke generation, while also improving thermal and acoustic insulation, offering strong potential for application in transportation interiors, lightweight flame retardant panels, and multifunctional building insulation materials.