Sustainably sourced and carrageenan-based hydrogels as fireproof coatings for the protection of wooden constructions during wildland urban interface fires

Existing hydrogel coatings for fire prevention, which are mainly based on chemically synthesized polymers, have environmental burdens and low adhesion. They dry easily at high temperatures and strong winds, limiting their use. Here, we propose a novel marine polysaccharide-based flame-retardant hydrogel coating. This coating has inherent flame-retardant properties and strong adhesion due to strong molecular interactions. It is made entirely of bio-based materials and forms a protective char layer when dry, preventing the substrate from catching fire. Compared with untreated wood, hydrogel-coated wood had a significantly longer ignition time of 67 ± 5 s, a 24.17 % reduction in the total heat release (THR), and a 37.2 % reduction in heat release rate (HRR), whereas the fire performance index (FPI) improved from 0.04 m²/(s·kW) to 0.17 m²/(s·kW), and the fire growth index (FGI) decreased from 3.49 kW/(m²·s) to 1.57 kW/(m²·s), improving the overall safety of wood materials. In addition, the coating has excellent antimicrobial properties, up to 99 % against E. coli and S. aureus, which is vital for fire protection in special situations, such as protecting grain silos, fighting wildfires and maintaining timber structures.