Study on the preparation and inhibition mechanism of intumescent nanogel for preventing the spontaneous combustion of coal

[Display omitted] •This manuscript mainly studied an intumescent nanogel.•Inorganic nanoparticles are combined with intumescent flame retardant system.•Free radical and functional group analysis proved good inhibition effects.•Physical, chemical and composite inhibition mechanism was analyzed. A green, halogen-free, efficient, stable, and low-cost intumescent nanogel (ING) was prepared by combining an inorganic nanoparticle flame-retardant system with a chemical intumescent flame-retardant system. Polyacrylamide (PAM) gel was prepared by solution polymerization, then the modified nano-silica (MNS) and intumescent flame retardant were added to the PAM gel successively to prepare the ING. The preparation mechanism was analyzed, and response surface analysis showed that the optimal addition ratio of acrylamide, MNS, and potassium persulfate was 10:0.4:0.07, and the optimal reaction temperature was 75 ℃. The modification of nano-silica and the surface morphology of the composite gel were observed by scanning electron microscopy. In the electron spin resonance experiment, the free radical concentration of 5.70131 × 1017/g of the ING inhibited coal was significantly lower than other coal samples. The content of aliphatic hydrocarbon, aromatic hydrocarbon, and the oxygen-containing functional group in the in situ diffuse reflection Fourier transform infrared spectroscopy experiments all indicated that the ING achieved an excellent inhibition effect. Finally, the inhibition mechanism of the ING was analyzed for its physical, chemical, and composite effects. The PAM gel, MNS, and the intumescent flame retardant system demonstrated a triple inhibition effect, which indicates that ING is an ideal material for preventing the spontaneous combustion of coal.