Novel authigenic gas foaming hydrogels for preventing coal spontaneous combustion

Authigenic gas foaming hydrogels were synthesized using chitosan (CS), acrylic acid, and attapulgite (APT) as hydrophilic monomers; potassium persulfate as initiator; N,N'-methylenebisacrylamide as cross-linker; and sodium carbonate (Na2CO3)/acetic acid as foaming agent. Effects of different monomers, amount of foaming agent, and temperature on swelling ratio (SR) of the hydrogels were examined. Morphology, structure, and thermal stability of authigenic gas foaming hydrogels were studied using field emission scanning electron microscope, Fourier-transform infrared spectroscopy, and synchronous thermal analysis. Scanning electron microscope images reveal apparent pores on hydrogels, produced by foaming agent Na2CO3/acetic acid. Therefore, more foaming agent would bring more pores on hydrogels. Synchronous thermal analysis results suggest that higher amount of CS would result in higher thermostability of hydrogels. However, APT has no substantial effect on thermal stability. SR decreases with increasing amount of CS. Hydrogels prepared at 70 degrees C reaction temperature exhibit maximum swelling. Furthermore, SR decreases with higher covalence of saltion.