Sustainable chitosan composite foams: Synergistic hydroxyapatite nanowires / phytic acid-melamine hybridization for...

Fire safety remains a critical global challenge, as conventional fire protective materials focus on passive insulation/flame retardancy but lack active early-warning for incipient fires. Chitosan (CS)-based foams are promising for fire protection but suffer from inherent flammability, limiting practical use. Herein, CS-based foams composited with hydroxyapatite nanowires (HAP NWs) and phytate-melamine (PA/MEL) were fabricated via freeze-drying, forming an "active warning-passive protection" system. Structural characterizations confirmed uniform dispersion of HAP NWs and PA/MEL in CS matrix via hydrogen/ionic bonding. Thermogravimetric analysis revealed CS-HAP-10PA/MEL had 61.6% char residue at 750 °C (N₂), a 105.3% increase vs. pure CS. CS-HAP-10PA/MEL exhibited a limiting oxygen index (LOI) of 45.0% and a 76.3% lower peak heat release rate (pHRR) than pure CS, manifesting excellent flame retardancy. Fire warning tests indicated that CS-HAP-5PA/MEL triggered an alarm within 4.2 s (signal stable >60 s) upon exposure to flame and exhibited sensitive responsiveness at 60-200 °C (0.8 s response at 120 °C). A 6 mm-thick CS-HAP-5PA/MEL (36.6 mW/ (m^.K)) sample reached only 61 °C surface temperature after 5 min at 120 °C (14.2 °C lower than pure CS), demonstrating good thermal insulation. This foam integrates warning, flame retardancy, and insulation, offering a novel strategy for intelligent fire protective materials.