Study On Preparation And Characteristics Of Natural Polysaccharide Grafted Hydrogels For Prevent Coal Spontaneous Combustion

Hydrogel is a kind of polymer with three-dimensional structure.Because it has good water absorption and water retention ability and is safe and non-toxic,hydrogel has been used as a new fire extinguishing material to prevent coal spontaneous combustion in recent years.In view of the high cost of preparing hydrogels,in this study,lignin(Lg)and chitosan(CTS)were grafted with acrylic monomers to prepare two kinds of natural polysaccharides grafted hydrogels,which not only reduced the cost and realized the high value utilization of natural polysaccharides,but also improved the basic ability of acrylic hydrogels.It has the advantages of green environmental protection,non-toxic and harmless,having good inhibitory effect and so on.The specific research contents and results are as follows:(1)Ammonium persulfate(APS)was chosen as initiator and N-N'-methylene bisacrylamide(MBA)was chosen as crosslinking agent.The chitosan grafted poly(acrylic acid-co-methacrylamide)(CTS-g-P(AA-co-MAAm))hydrogel and lignin grafted poly(acrylic acid-co-N-isopropylacrylamide)(Lg-g-P(AA-co-NIPAm))hydrogel were synthesized by aqueous solution polymerization.The effects of various factors on the water absorption ratio of hydrogels were studied.In the optimal preparation process,the equilibrium water absorption ratio of CTS-g-P(AA-co-MAAm)hydrogel was 132 g/g and the equilibrium water absorption ratio of Lg-g-P(AA-co-NIPAm)hydrogel was 25 g/g.(2)water retention experiment and compression experiments showed that the change of the basic characteristics of chitosan hydrogel was mainly reflected in the water retention capacity and compressive strength.In the water retention experiment both at room temperature and 90 ~oC,the water retention time of chitosan grafted hydrogel was longer than that of ungrafted hydrogel,and its compressive strength was nearly doubled than that of ungrafted hydrogel.By scanning electron microscope and thermogravimetric analysis,it was found that the change of lignin on the basic characteristics of hydrogel was mainly reflected in the surface microstructure and thermal stability.The lignin grafted hydrogel showed a unique porous spongy structure on the surface.Compared with that of ungrafted hydrogel,the temperature of the maximum weight loss rate increased by 28 ~oC and the residual carbon at 600 ~oC increased by 11%.(3)The inhibitory effect of two kinds of polysaccharide grafted hydrogel with different dosage on coal was studied by using synchronous thermal analyzer.The results showed that the optimum dosage of CTS-g-P(AA-co-MAAm)hydrogel is 5%and the optimum dosage of Lg-g-P(AA-co-NIPAm)hydrogel is 10%.Finally,according to the change of coal-like functional group and the kinetics of coal-oxygen reaction,it is found that both hydrogels can inhibit the active functional groups(methyl,methylene and hydroxyl groups)of coal to participate in the chemical reaction at low temperature.At high temperature,Lg-g-P(AA-co-NIPAM)hydrogel has stronger inhibitory ablility than CTS-g-P(AA-co-MAAm)hydrogel,which can effectively improve the reaction energy barrier of coal and make it more difficult to spontaneous combustion.