Preparation and characterization of highly stable double-crosslinked gel foam for inhibiting coal spontaneous combustion

In order to enhance the stability and address environmental concerns related to fire prevention and extinguishing foam materials in coal mines, this study designed an environmentally friendly and highly stable gel foam (DF) featuring a double-crosslinked structure and flame-retardant effects. Based on the ionic crosslinking reaction between sodium alginate (SA) and Ca2+ ions, carboxymethyl cellulose sodium (CMC) is introduced for hydrogen bonding crosslinking with SA, creating a dual-crosslinked structure involving both physical and chemical interactions. SEM observation revealed that the pore structure of the double-crosslinked gel is denser compared to the single-crosslinked gel. FTIR analysis confirmed that DF undergoes both physical and chemical crosslinking processes. The optimal concentration of foaming agent (AG) was determined to be 0.3 wt% through surfactant compounding experiments. Subsequently, the effect of calcium ethylenediaminetetraacetate (EDTA-Ca) and Gluconic acid-δ-lactone (GDL) on DF gelling time and foam properties were analyzed through single-factor experiments. Optimal concentrations of the EDTA-Ca and the GDL were determined to be 0.015 mol/ L and 0.9 wt%, respectively. The gelation time of DF was 6 minutes, with a half-life of 45 days and a foam volume of 475±10 mL. The half-life and foam volume of DF have significantly improved compared to the previous foam. Microscopic structure and film-forming properties analysis indicated that DF exhibits a smaller foam size and could form a dense and uniform film compared to other foams, effectively suppressing the oxidation reaction of coal. Thermogravimetric (TG) and temperature-programmed oxidation tests showed that DF could increase the temperature points of the maximum water loss rate and weight loss rate of coal, and had a higher inhibition rate compared to traditional water-based foam. The fire extinguishing test indicated that DF exhibited a faster extinguishing speed than traditional water-based foam. In this work, environmentally friendly materials were employed to prepare a highly stable gel foam aimed at inhibiting coal spontaneous combustion.