Study on Tannic Acid/Carboxymethyl Cellulose-Based Hydrogel for Suppressing Coal Spontaneous Combustion

Traditional hydrogels face limitations in suppressing coal spontaneous combustion due to their reliance on physical mechanisms (heat absorption and oxygen isolation) and lack of chemical inhibition, compounded by intricate preparation procedures. To address these limitations, this study developed a CAA-TA composite hydrogel with synergistic physical-chemical inhibition properties. The hydrogel was synthesized using carboxymethyl cellulose (CMC) as the matrix, acrylamide (AM) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as copolymerization monomers, and tannic acid (TA) as an antioxidant. The optimal formulation was determined by optimizing gelation time, water retention, and permeability to meet mine fire prevention requirements. Fourier transform infrared spectroscopy (FTIR) confirmed the successful grafting of AM-AMPS onto the CMC backbone, while hydrogen bonding interactions between the hydroxyl groups of CMC, phenolic hydroxyl groups of TA, and N-H groups of AM contributed to a stable three-dimensional network structure. Scanning electron microscopy (SEM) revealed a dense wrinkled surface and honeycomb-like porous morphology, which enhanced water confinement through physical entrapment and capillary effects, endowing the hydrogel with high water retention and stability. Programmed heating tests highlighted superior low-temperature inhibition, with CAA-TA treated coal exhibiting 52.2% and 56.7% reductions in CO emissions at 100°C and 180°C, respectively, outperforming TA-free counterparts. Fire suppression trials demonstrated rapid temperature reduction from 800°C to 88.9°C within 30 min without re-ignition, surpassing conventional CAA hydrogels. The CAA-TA composite hydrogel achieves efficient coal spontaneous combustion inhibition through a synergistic mechanism combining heat absorption/oxygen isolation and radical scavenging/antioxidant effects. This study advances the design of multifunctional fire-retardant materials through rational integration of physicochemical strategies.