Preparation And Properties Of Mining Polyurethane Foams Modified With Magnesium-aluminum Hydrotalcite Based Composite Flame Retardants

During the coal mining process,due to the influence of mining disturbances,it is easy to damage the reserved coal pillars and sealing walls,leading to deformation and collapse of the coal pillars,and the occurrence of air leakage,which may lead to coal spontaneous combustion disasters and affect the safe mining of the working face.The polyurethane foam material can be used to reinforce the broken coal and rock mass,fill the caving area,and seal the air leakage.However,the ultimate oxygen index of polyurethane filling materials is only about 19.0%,which is a flammable material.The heat released during the filling process can indirectly promote the oxidation of fractured coal and rock masses,leading to fires in the filling area and even secondary accidents such as coal spontaneous combustion and gas explosions.Although the traditional flame retardant methods have certain effects on the improvement of the flame retardancy of polyurethane foam,with the improvement of the requirements for air leakage plugging and safety industry standards,the current materials can no longer meet the plugging requirements for underground use in terms of flame retardancy,heat release and smoke.Therefore,this thesis developed a new type of flame-retardant polyurethane foam for mining,which provides a theoretical basis for the safe use of organic foam for mining.In this thesis,the preparation and related characteristics of flame retardant polyurethane foam materials were systematically studied through theoretical analysis and experimental research,and the following research results were obtained:The effects of phase change material palmitic acid on the maximum reaction temperature and comprehensive properties of polyurethane foam were studied,and the optimal proportion was determined.The results showed that the addition of palmitic acid had little effect on the flame retardancy of polyurethane foam;The maximum reaction temperature decreases with the increase of the amount of palmitic acid added.When the addition amount is 5%,the maximum reaction temperature decreases from127℃to 96℃.At this time,the cell structure is stable,the compression strength is increased by 1.4 k Pa,and it has good thermal stability.The modification effects of various flame retardant systems（modified LDHs,APP,MPP,modified LDHs/APP,modified LDHs/MPP）with different addition amounts and ratios on flame retardancy and smoke suppression of polyurethane foam materials were studied,and four flame retardant formulations with better flame retardancy were determined.The results showed that the flame-retardant properties of polyurethane foam materials were improved in varying degrees after adding different flame retardants.Compared with the single flame retardant,the flame retardant and smoke suppression effects of the compounded polyurethane foam materials were enhanced;APP20/PUF,MPP20/PUF,LDHs4/APP16/PUF,LDHs4/APP16/PUF have the best flame retardancy and smoke suppression effects.Among them,the limit oxygen index of the sample LDHs4/APP16/PUF is 25.6%,and the vertical combustion reaches the V-0 level.The smoke density level is reduced from 47.98 to 22.36.The structure and flame retardant mechanism of polyurethane foam modified by four efficient flame retardant schemes were studied,and the best combination scheme was determined.The results show that the addition of flame retardant has little effect on the maximum reaction temperature of polyurethane foam;Based on the analysis of the cell structure,compression strength and thermal stability of four flame retardant modified polyurethane foam,it was found that LDHs4/APP16/PUF had the best performance,its compression strength was the smallest difference from the pure polyurethane foam before modification,the cell size was uniform,and the compression strength was 150 k Pa;The residual carbon rate increased from 2.19%to 14.77%,enhancing thermal stability.The modified LDHs and APP have synergistic flame retardancy.Through heat absorption,surface covering,charring,combustion chain inhibition and other functions,they play a role in the gas phase and condensed phase,and achieve the efficient flame retardancy of polyurethane foam.The combustion characteristics of flame-retardant polyurethane foam for mining were studied,and the influence of polyurethane on the thermodynamic characteristics and gas production characteristics of coal oxidation combustion was explored.The experimental results show that the ignition time of the modified flame retardant polyurethane foam（LDHs4/APP16/PUF）is 32 s,the peak heat release rate,the total heat release amount are the smallest,and the performance is the best;The ignition point of the mixed sample of coal and polyurethane decreases,and the activation energy in the combustion stage decreases.The polyurethane foam has a synergistic effect on the oxidative combustion of coal;The polyurethane foam with modified magnesium aluminum hydrotalcite and ammonium polyphosphate as flame retardants reduces the promotion of coal oxidation and combustion to a certain extent,and plays a certain role in inhibiting combustion;The presence of polyurethane can promote the conversion of CO into CO₂,increase the release of CH₄ and C₂H₄,reduce the release of C₂H₆ and C₃H₈,and have early or delayed peaks.This has certain guiding significance for determining whether spontaneous combustion disasters occur in the area where polyurethane is used underground.The thesis has 42 figures,24 tables and 103 references.