Regulating smoke precursors and enhancing durability of flexible polyurethane foam via reactive hyperbranched P-N flame retardant

A fire safety FPUF was designed by using only 8 wt.% reactive flame retardant. • Resultant FPUF showed excellent smoke suppression, reducing TSP (−79.3%) and smoke density (−83.1%). • 42.7% and 50.7% reductions in pHRR and THR of FPUF-HTMP8 were achieved. • A smoke precursor regulation mechanism was experimentally verified. • The mechanical properties and fire safety for FPUF-HTMP8 were effectively maintained. Flexible polyurethane foam (FPUF) is highly flammable and releases lethal toxic smoke during combustion, primarily derived from isocyanate-containing structures. Furthermore, adding flame retardants inevitably leads to migration and failure issues. This study addressed the neglect of smoke-suppression mechanisms by synthesizing a phosphorus-nitrogen reactive flame retardant (HTMP). HTMP chemically incorporates into the polymer network via its multi-reactive sites, actively regulating thermal degradation pathways. Results demonstrated that 8 wt.% HTMP modified FPUF achieved a limiting oxygen index (LOI) of 24.1%, passed the HF-1 rating, and exhibited a 53.3% reduction in total heat release (THR). Notably, total smoke production (TSP) and smoke density decreased by 79.3% and 83.1%, respectively. It was demonstrated that HTMP regulated the reaction pathway of isocyanates produced by thermal decomposition of polyurethane through its hydroxyl groups and the amine structures generated by degradation, inducing cross-linking and cyclization reactions, and suppressing the production of smoke precursors from the source, inhibiting toxic volatiles (HCN). In addition, due to terminal hydroxyl groups, HTMP entered the FPUF network, endowing the material with excellent long-term service stability and improved mechanical properties. This research provides new insights for designing fire safety FPUF samples with low smoke release materials from a reaction pathway perspective.