Preparation and Fire-Retardant Mechanism of Self-Hardening Silica Foam for Wood Fire Prevention

Considering the hazard of wood fire is one of the major cataclysms in nature, an effective way to prevent the loss of wood fire should be studied, such as fire-resistant materials. In this work, a novel silica foam with controllable gelation time was developed and tested for its fire-retardant effect and mechanism on wood. The optimum formula is 0.4wt% compound foaming agent (SDS: SDBS: APG = 3:3:2), 0.1wt% foam stabilizer (CMC-Na), 30 vol.% sodium silicate solution and 40 vol.% acetic acid. The fire-retardant mechanism of silica foam on wood was investigated through X-ray photoelectron spectroscopy (XPS), X-Ray Diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Thermo Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and fire retardance analysis. XPS and XRD results indicate that the silica foam contributes to the formation of a thermal stable layer on the wood surface for fire retardancy, and the hydrophilic groups (C-O and C = O), especially the C-O functional group accounts for approximately 95% of the entire carbon-containing functional group in the silica foam, and amorphous silica in the silica foam can adsorb water physically or chemically, helping to provide a wetting effect for fire retardancy. FTIR result indicates that the Si–O-C and Si–C bonds formed between the silica foam and wood can promote the formation of a charred layer at high temperature, reinforcing the fire retardancy. TGA and fire retardance analysis results indicate that the silica foam can inhibit the pyrolysis reactions of wood, and the mass loss rate of the wood is reduced by 50% and 30%, respectively.