Study On Low Exothermic Properties Of Mine Polyurethane Foam Modified By Expanded Graphite-Based Hydrated Salt Phase Change Material

With the development of chemical industry,polymer has been applied more and more widely in coal mines.Polyurethane foam,as a foam filling material,has the characteristics of high foaming rate,adjustable curing time and excellent leak-plugging effect.However,when used underground,polyurethane foam requires in-situ foaming curing and releases a lot of heat,and polyurethane foam has poor thermal conductivity.Heat exchange with the external environment is slow,heat accumulation is easy,may cause mine fire accidents.In order to solve the problem of reaction exothermic heat release of mining polyurethane foam,an expanded graphite-based hydrated salt phase change material was prepared in this study for the foam curing process of mining polyurethane foam to reduce the maximum temperature in the process of use,achieve low heat release of mining polyurethane foam and improve its safety.The following results were obtained:The heat release principle of polyurethane foam was studied and the evaluation method of heat release characteristics was established.The results show that:The heat release during the use of polyurethane foam comes from foaming reaction and gel reaction.An experimental platform was established to evaluate the heat release of polyurethane foam.The influence of single hydration salt material on polyurethane foam was analyzed,and it was found that the reaction temperature could be reduced from 140℃to less than 100℃with the addition of 15%.However,the water generated by phase transition has a great influence on polyurethane foam,resulting in the phenomenon of simultaneous bubble collapse.The preparation of expanded graphite-based hydrated salt phase change material was completed.In order to solve the effect of water on the performance of polyurethane foam,the hydrated salt material was adsorbed by expanded graphite（EG）.The expanded graphite was prepared by microwave method,and its hydrophilicity was modified by NP-40 and hydrophilic nano silica.The expanded graphite modified by 5%hydrophilic nano silica was optimized and combined with the sodium acetate trihydrate material modified by 1%CMC and 2%disodium phosphate dodecahydrate by screening.Finally,hydration salt phase change materials with different amounts of EG were prepared.Thermal conductivity,leakage and phase change enthalpy values of the above materials were tested.It is found that the thermal conductivity of the composite material added with 6%EG is 1.9421 W·m^-1·K^-1,no leakage,latent heat of phase transition is 236.304 J/g,and the performance is the best.Low exothermic polyurethane foam for mining was prepared.Sodium acetate trihydrate,expanded graphite based hydration salt phase change materials EG-2 and EG-6 were added to polyurethane foam in different proportions.It was found that 10%EG-6 added polyurethane foam has the characteristics of uniform morphology,stable performance,appropriate foaming curing time,and can reduce the reaction temperature to 91.4℃.The infrared and thermogravimetric characterization of polyurethane foam before and after modification showed that the modified low exothermic polyurethane foam had lower reaction degree but better thermogravimetric stability.The decomposition of polyurethane foam before and after modification was divided into two main stages.The kinetic calculation results show that the second stage activation energy of the modified polyurethane foam increases from 104.13 k J/mol to 112.93k J/mol.The heat storage temperature of medium volume polyurethane foam before and after modification was tested by a customized mold.The results show that the maximum reaction temperature of modified polyurethane foam is less than 100℃,which is much lower than 140℃before modification.The temperature distribution is characterized by high center temperature of foam body and low edge.And the time to drop to room temperature is reduced from 240 min to 140 min,which improves the safety of use and conforms to the standard of AQ1089-2020"Polymer Materials for Coal rock Reinforcement in Coal Mine".The decomposition characteristics of low exothermic polyurethane foam were studied and the gas production characteristics of low temperature oxidation of polyurethane foam mixed with coal were revealed.In situ infrared spectroscopy was used to test the polyurethane foam before and after modification.It was found that the strength change of the characteristic group-N=C=N-of polyurethane foam was related to the oxidative decomposition of-N=C=O.The modified low exothermic polyurethane foam did not change the decomposition process of the hard and soft segments of polyurethane,but the decomposition characteristic temperature point increased from246℃to 263℃.The results show that the stability of the modified polyurethane foam is improved.A cylindrical polyurethane foam mold is designed.The experimental results of low temperature oxidation of polyurethane foam in the presence of coal show that there is a synergistic effect of mutual promotion between polyurethane foam and coal,which makes the intersection point advance,polyurethane foam oxidizes before230℃,deformation will occur and air leakage channel will be generated,and the shape variable of the modified low exothermic polyurethane foam is smaller.Under this condition,oxygen consumption and CO production decreased,while CO₂ and C₂H₄production increased.This thesis has 52 maps,11 tables,93 reference articles.