Study On Preparation Of Montmorillonite Type Double Network Composite Gel And Its Fire-fighting Characteristics

Coal spontaneous combustion seriously threatens the sustainable development of the coal industry during the mining process.The flame-retardant fire-extinguishing performance of mine fire-extinguishing materials is one of the key technical bottlenecks restricting the effect of mine spontaneous fire prevention,and how to improve the performance and application range of gel fire-extinguishing materials has become a hot and difficult point in current research.Gel fire-fighting technology is currently one of the widely used technologies in mine fire prevention all over the world duo to strong water retention performance,good fluidity and thermal stability of gel,and it can effectively wrap coal and fill cracks to achieve oxygen isolation via covering and sealing coal.Based on the performance advantages of organic polymer gels and the unique structural characteristics of nano-polymer materials,this paper proposes a composite gel that can prevent coal spontaneous combustion and fires together with dual-network gel and nano-materials.The composite gel is made up of double network gel and montmorillonite.Among them,the double network gel is the first network formed by cross-linking polyvinyl alcohol(PVA)and boric acid under alkaline conditions,and the high molecular network,which was cross-linked by hydrogen in flexible matrix polyacrylamide PAM/PVA intermolecular,is the second network.The optimal ratio of composite gel used in fire prevention was obtained by orthogonal experiment,analyze the influence of montmorillonite,PVA and PAM components on the gel performance,gel time and permeability test.The experimental results show that:PVA has the greatest influence on the gelation time,and the change of PAM concentration has the strongest influence on the gel permeability.The optimal blending ratio is 3%montmorillonite+3%PVA+1.5%PAM and 4%montmorillonite+2.5%PVA+1.5%PAM gel.Based on the 3%montmorillonite+3%PVA+1.5%PAM composite gel system,the gel's comprehensive performance such as viscosity,strength,water retention and thermal stability were investigated,and the influence of different factors on the gel performance was studied.It is concluded that PVA has a great influence on the gel viscosity.When the PVA concentration increases from 2.5%to 3.5%,the gel viscosity increases by 77.6%,and when the boric acid concentration is 1-1.5%,there is a critical value,which makes the gel viscosity the largest.The overall strength and water retention of the composite gel are greater than that of the double network gel.In addition,before the composite gel 120?,the weight loss rate changes little,and there is a sudden change at 120?,then the weight loss rate continues to increase at a slow rate,and the weight loss change rate is lower than the double network gel.With the montmorillonite content increase,the weight loss rate of the composite gel gradually decreases.Taking long flame coal,lignite and coking coal as the research objects,the chemical flame retardant properties of the composite gel are studied by using the resistance performance test,the change of mass and heat,and the determination of active functional groups.The experimental results show that the inhibition effect of 4%montmorillonite composite gel is better than that of 3%montmorillonite composite gel,and the temperature of the cross point is obviously lagging behind;at 200?,the inhibition rates of XM,SD and GD coal treated with 4%montmorillonite composite gel were 41.40%,32.26%and 27.21%,respectively.In addition,the 4%montmorillonite composite gel treatment reduces the weight loss rate in the initial weight loss stage of the coal sample,reduces the weight gain of the coal sample during the weight gain stage of oxygen absorption,and increases the activation energy at each stage.The hydroxyl and carbonyl content of coal is always lower than that of raw coal,and the content of C-H is always higher than that of raw coal.Combining the physical and chemical flame-retardant properties of the composite gel,the flame-retardant and fire-extinguishing mechanism can be discussed.The flame retardant effect of the composite gel is achieved through the existence of a large number of-OH,-COOH,-COONH₂ and other hydrophilic groups in the PVA and PAM,which form various types of hydrogen bonds with water molecules,and the water absorption and expansion effect of montmorillonite.In this way,the double water retention effect of the composite gel is realized.And,because the gel has strong viscosity and fluidity,it can permanently seal and fill the coal body and reduce the amount of oxygen adsorption.In addition,the free hydroxyl groups in coal are adsorbed by a large number of hydrophilic groups inside the organic polymer and converted into stable hydroxyl-containing compounds,and the chain reaction of oxygen-containing compounds is interrupted,which acts as a chemical hindrance.The overall performance of the composite gel's flame retardant effect is that in the early stage,the good water retention of the gel is used to delay the release of water molecules and enhance the retention time of water molecules;in the later stage,the thermal stability of montmorillonite is fully utilized to continuously isolate oxygen and prevent re-ignition.