Preparation And Study On Safety Performance Of Pre-grouting Material And Its Application In Coal Seam Gas Pressure Measurement Method

With the development of national economy,more and more polymer materials have been applied to coal industry.As to gas prevention and control,there are more and more cases in which polymer materials are applied to mine gas pressure measurement.The use of polyurethane as a sealing material in coal seam gas pressure measurement method is a practical method developed in recent years.On the one hand,polyurethane material can play the role of reinforcing the loose layer of coal around the borehole holes along seam,and on the other hand can seal the cracks to give better conditions for pressure measurement process.However,it is found that the viscosity of polyurethane raw material is high and the permeability to the coal seam is insufficient during the gas pressure measurement process.When higher injection pressure is applied,polyurethane material will travel a long distance along the crack of the loose layer,the loose layer around borehole is not effectively reinforced.In addition,safety performance of polyurethane is insufficient,such as high curing process temperature and poor flame retardant performance.Mine fires caused by polyurethane application occur from time to time,which seriously limits the application of polyurethane in mines.Therefore,it is necessary to develop a new type of low-viscosity and high-permeability sealing material.The new material must first own the characteristics of low viscosity,and better penetration ability than polyurethane under normal or low injection pressure conditions.These characteristics enable new material to adhere the coal matrix better and reinforce the loose layer;secondly,new material must have a suitable curing reaction completion time to ensure we have sufficient time for the material to be injected into the coal seam;Finally,new material must have high safety performance,such as low reaction curing temperature and high flame retardant ability to ensure its safe application to coal industry;new materials with these properties can better permeate into coal seam to seal cracks and adhere coal matrix,so as to be applied to coal seam gas pressure measurement method.In this paper three kinds of composites system were prepared using polylactide polyol/PEG 200/PEG 600,polyether polyol 4110 and isocyanate as raw materials,and polylactide polyol/polyether polyol 4110/isocyanate(composites system 1)were selected as target system(basic formula)for further retardant and mechanical modification experiment.Compared to conventional materials polyurethane,the newmaterial has lower curing temperature,lower viscosity and higher permeability.After polylactide polyol is added into composites system 1,Tmax decreases,and Tc becomes longer.The ideal foumula with good foaming performance is selected when mass ratio of polylactide polyol:polyether polyol 4110:isocyanate equals to 4:6:10(2:3:5)after vertical burning test,integrated thermal analysis,raman spectrometer analysis and X-ray powder diffractometer analysis were conducted.And the new composites can be well applied to mine gas pressure measurement.In order to improve the flame retardant performance of new materials,bio-based benzoxazine(Boz-F)was synthesized,and it was used as carbon-forming agent for intumescent flame retardant.integrated thermal analysis,thermal degradation process analysis and DSC show that Boz-F has a high carbonation rate and suitable activation energy,therefore it is suitable for intumescent flame retardant component.When the mass ratio of Boz-F: red phosphorus: melamine equals to 2:1:2,the composites have the best flame retardant performance.Mechanical modification experiment was also adopted to the new materials,and hollow glass microspheres were selected as additive.the composite material have better mechanical properties than before after modification.The permeability and bonding property between new materials and coal matrix were also investigated.It shows new materials have better permeability than conventional material Polyurethane.In order to analyze the bonding property,mechanical properties of new material-coal matrix mixture were tested.It was also found that,new materials have better bonding propertity than Polyurethane.Because hollow glass microsphere were used for modification experiment,the author gave new explanation of the interaction between inorganic particles and polymer matrix using "particle size parameter".Besides the "particle size parameter" was verified using classical model.Finally,the comparative experiments were carried out with new materials and polyurethane materials using "gas pressure determination method of sealing whole borehole with polymer materials".The experimental results show that the borehole sealed with new materials is superior to that of polyurethane materials in both loose layer reinforcement and final measured pressure.