Rapidly deployable bio-based chitosan/phytate polyelectrolyte hydrogel coatings for flame retardancy and short-term thermal protection of cotton fabrics

Cotton fabrics are highly flammable cellulose-based textiles that are prone to rapid flame spread and smoldering, creating serious fire safety risks. Hydrogel coatings offer a promising route for textile fire protection because their water-rich networks can absorb heat through evaporation and subsequently form thermally insulating char barriers. However, many reported hydrogel coatings require complex preparation, external curing, or long processing times, which limits their rapid deployment. Herein, a rapidly deployable bio-based organic hydrogel coating, denoted as HP hydrogel, was fabricated at room temperature through electrostatic self-assembly between quaternized chitosan (HTCC) and sodium phytate (PA-Na). The optimized coating could be directly applied onto cotton fabrics after fast gelation, combining water retention, substrate adhesion, flame retardancy, and short-term thermal shielding. PA-Na promoted the regulation of thermal degradation and char-forming ability of the HTCC network, enabling the coated cotton fabric to reach a limiting oxygen index of 31.5%. Microscale combustion calorimetry (MCC) showed that the H 1 P 1 hydrogel reduced the peak heat release rate and total heat release by 32.9% and 34.4%, respectively, compared with the PA-Na-free hydrogel. Residual char analyses confirmed the formation of a compact phosphorus-containing carbonaceous layer, indicating a dominant condensed-phase flame-retardant mechanism. In direct-flame thermal protection tests, the H 1 P 1 hydrogel protected skin-surrogate tissue for 120 s under exposure to a 1300 °C flame, while maintaining the subcutaneous temperature below 55 °C. This work presents a simple and rapidly applicable bio-based hydrogel coating strategy for improving the flame retardancy and short-term fire protection of cellulose-based textiles.