Nacre-inspired phosphorylated chitosan / MXene / hydroxyapatite nanowire composite films with ultrafast fire warning and intrinsic fire safety

Developing intelligent fire-safe materials with integrated flame retardancy and rapid fire-warning capability remains a major challenge for next-generation thermal safety systems. In this work, a flexible nacre-inspired multifunctional composite film was successfully fabricated by integrating phosphorylated chitosan (PCS), MXene nanosheets, and hydroxyapatite nanowires (HAP NWs) through a vacuum-assisted filtration strategy. Benefiting from the synergistic effects of phosphorus-induced catalytic charring, MXene-derived barrier protection, and HAP NW-reinforced structural stabilization, the composite film exhibited significantly enhanced thermal stability, flame retardancy, and fire-warning performance. Compared with the pristine chitosan film, the peak heat release rate was reduced by 81.7%, while the composite film achieved an ultrafast fire-warning response time of 0.37 s with stable alarm duration under direct flame exposure. Condensed-phase and gas-phase analyses revealed that the synergistic integration of PCS, MXene, and HAP NWs effectively suppressed combustible volatile release and promoted the formation of a stable inorganic-carbonaceous protective layer. This work provides a promising strategy for developing next-generation bio-based intelligent fire-safe materials for applications in energy storage systems, cable fire protection, and thermal safety management.