A slow-release ionic crosslinking strategy for a sprayable ceramifiable sodium alginate hydrogel toward sustainable wildfire suppression.

Developing spray-applied fire-retardant materials for wildfire suppression requires rapid deployment, effective surface retention, and sustained protection after water loss and during prolonged heating. This poses a significant challenge to traditional water-based fire-retardant materials, whose protective effectiveness often decreases as water evaporates. Herein, a sprayable ceramifiable sodium alginate-based hydrogel is developed, enabled by the gradual release of Ca2+ from the CaCO3/GDL system under ambient conditions. The hydrogel retained water for up to 17 h at 60 °C. Among all formulations, the incorporation of montmorillonite provided the best overall fire-protection performance, prolonging the ignition time to 215 s and reducing the peak heat release rate, total heat release, and total smoke release by 67.3%, 21.5%, and 62.7%, respectively. During combustion, the sodium alginate/Ca2+ gel network progressively transformed into a compact carbonaceous-inorganic residue, forming a ceramic-like barrier through the integration of carbonaceous and aluminosilicate-containing components. This work establishes a practical strategy for designing low-cost, spray-applied, bio-based-polymer fire-protection materials for sustainable wildfire prevention.