Preparation and Properties of CMC-Based Composite Gel as a Flame-Retardant Dust Suppressant

To address the challenge of balancing flame retardancy and dust suppression in conventional coal mine treatment materials, a multi-component synergistic flame-retardant dust-suppressant gel was fabricated using carboxymethyl cellulose (CMC) as the matrix, compounded with ammonium polyphosphate (APP), zinc borate (ZB), and polycarbodiimide (PCDI) as a cross-linking agent. The optimal formulation was determined via orthogonal experimental design combined with performance characterization, yielding a composition of 1 wt% CMC, 8 wt% APP, 2 wt% ZB, and 0.5 wt% PCDI. Systematic evaluations—including wettability tests, thermogravimetric analysis, and fire-extinguishing trials—demonstrated that the resultant CMC-based composite gel exhibits excellent structural stability and environmental tolerance. Specifically, the contact angle on the coal surface decreased sharply from 72.8° to 17.2°, and the mass loss rate after 30 min of wind erosion was merely 4.16%. Treatment with the gel elevated the critical temperature of the coal–oxygen reaction from 70 °C to 80 °C and reduced CO emissions by 40% at 170 °C. Furthermore, the temperatures corresponding to the maximum weight loss rate, ignition, and burnout increased by 12.9 °C, 16.8 °C, and 28.9 °C, respectively. Fire suppression tests revealed that the gel rapidly cools high-temperature coal seams and effectively prevents reignition. Mechanistic investigations indicate that the CMC-PCDI cross-linked network synergizes with the APP-ZB phosphorus–boron flame-retardant system: the three-dimensional gel architecture provides physical encapsulation and water retention, while the intumescent char layer formed by APP-ZB offers efficient oxygen barrier protection. This study provides a reliable gel-based technical solution for the integrated prevention and control of coal dust pollution and spontaneous combustion disasters in underground mines.