Preparation and Properties of Silica Gel Foam as Fire-Retardant with High Water Retention for Wood

The fire hazard related to wood has gradually become a global problem for humankind; therefore, how to enhance the fire retardance of wood is becoming a major issue. In this paper, a novel silica gel foam with high water retention was prepared and tested for its fire retardance on wood. The effect of the components’ concentrations was analyzed in terms of the gelation time and water retention of silica gel foam. The fire-retardant mechanism of silica gel foam on wood was studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR); and the fire-retardant performance was investigated using the thermogravimetric analysis (TGA) and vertical burning test. The SEM results show that the surface of the wood fibers can be covered with silica gel foam to form a fire-retardant layer. XPS, XRD and FTIR results indicate that the silica gel foam can form a SiO₂ thermally stable layer and a charred layer with Si–O–C and Si–C bonds on the wood at a high temperature for fire-retardant effect. The hydrophilic group (C–O and C=O) and amorphous silica in the silica gel foam is able to adsorb water molecules, which contributes to providing a humid environment for fire retardancy of the wood. TGA and vertical burning test results show that the silica gel foam effectively inhibits the wood pyrolysis process and reduces the mass loss rate of the wood.