Molecular Dynamics Study On The Effect Of Molecular Structure On Thermal And Mechanical Properties Of BPA-type Epoxy Insulating Materials

The BPA type epoxy resin insulation materials cured by acid anhydride are widely used in the insulation of electric power equipment.The research and design of epoxy resin insulation materials with excellent heat resistance and mechanical properties is the key to meet the development requirements of high power density of power equipment.The thermal and mechanical properties of epoxy insulating materials are significantly affected by the molecular structure of epoxy crosslinking system.Based on molecular dynamics calculation method,the influence of molecular structure of anhydride curing agent and epoxy resin on the mechanical and thermal properties of crosslinked products was studied,and the influence of alicyclic epoxy on the mechanical and thermal properties of anhydride cured epoxy resin system was further studied.The main research contents were as follows:(1)The microstructure characteristics,thermal and mechanical properties of BPA type epoxy crosslinking system cured by anhydride with different molecular structures were studied.It was found that the FFV and MSD of the cured system were generally decreased with the increasing of PA,which was mainly due to the restriction of the stack between molecules by the methyl group on the molecular structure of MTHPA.The increase of rigid groups of benzene ring on the molecular structure of PA makes the modulus of the crosslinked system increase,and when MTHPA:PA is 7:3,the overall mechanical properties of the epoxy crosslinked system are the best.When the MTHPA and PA are 9:1,the Tg of epoxy crosslinking system is the highest.With the increase of crosslinking degree,FFV firstly decreases and then increases.The continuous formation of the network structure makes the molecular structure compact,and the movement ability of the molecular chain segment decreases gradually.(2)The microstructure characteristics and thermal and mechanical properties of epoxy crosslinking systems with different molecular structures of epoxy resins were studied.It was found that with the increase of epoxy resin polymerization degree,the Young’s modulus and shear modulus of the crosslinking model showed a trend of gradual increase,while the volume modulus and toughness generally increased at first and then decreased.The glass transition temperature reaches 411.3K when the polymerization degree of DGEBA is 1.67.The CTE in the glass state decreases with the increase of the polymerization degree,and tends to be stable when the polymerization degree is 1.67.The free volume fraction(FFV)and mean orientation shift(MSD)of the DGEBA crosslinking model reached the minimum when the degree of polymerization was 1.33,and the expansion and thermal motion of the molecular chain were inhibited at high temperature.The increase of temperature will decrease the modulus value of epoxy insulation material,which is related to the increase of FFV and MSD of the crosslinked system caused by the increase of temperature.(3)The microstructure and the changes of thermal and mechanical property parameters of the epoxy cross-linked system after the introduction of OSC molecular structure were studied.The study found that with the increase of the content of OSC molecules,the modulus value and glass transition temperature of the cross-linking system both increased first and then decreased.When the ratio of DGEBA:OSC is 7:3,the modulus value and Tg are the largest.The FFV and MSD of the cross-linked system both decreased first and then increased with the increase of the OSC ratio.The cross-linked network after the introduction of OSC inhibited the movement of molecular chains more strongly,and improved the thermal and mechanical properties of the composite system.The experimental data are in good agreement with the molecular simulation results,which verifies the effectiveness of the molecular simulation results.