Zhenyang Yin, Yitong Jiang, Fengyu Meng, Xiaoming Qi, Jiangsheng Chen, Hongbo Dai, Chen Qian, Yaqin Fu
Flexible polyurethane foam (FPUF) suffers from high flammability and environmental concerns, necessitating sustainable fire protection strategies. This work highlights a nacre-inspired, halogen-free flame-retardant coating with a hierarchical multicomponent “brick–mortar” architecture. Ammonium polyphosphate (APP) and sodium montmorillonite (MMT) act as rigid multiscale “bricks”, while Schiff base-modified chitosan (DCS) cross-linked with gelatin (GEL) forms the adhesive “mortar”, constructing a hydrogen-bonded, organic–inorganic hybrid network with robust interfacial compatibility on FPUF. The resulting FPUF/3A@M-D/G composite demonstrates remarkable fire safety, achieving a limiting oxygen index (LOI) of 32.6% and a UL-94 V-0 rating. Cone calorimetry shows significant reductions in pHRR 1 (−46.1%) and pHRR 2 (−67.7%), and THR (−16.8%), along with prolonged ignition time (from 4 to 6 s) and increased char yield (from 8.2 to 26.3 wt %). Meanwhile, the coating improves compressive strength (from 7.96 to 9.32 kPa) without compromising elasticity. Mechanistic analyses (SEM, FTIR, Raman, XPS, and Py-GC/MS) reveal a dual flame-retardant action of condensed-phase char reinforcement and gas-phase radical inhibition. This scalable bioinspired strategy provides a halogen-free pathway to simultaneously improve flame retardancy and mechanical robustness of FPUF for applications in transportation, furniture, and energy systems.