Study On The Effect And Mechanism Of Nano Al₂O₃ And Its Surface Modification On The Properties Of Meta Aramid Insulating Paper

Meta aramid paper has gradually become an indispensable insulating material in electric power equipment due to its excellent thermal stability.However,due to the lack of active groups on the surface of aramid fibers,the paper structure is porous,which can adversely affect its breakdown strength and electrical conductivity.The doping of micro and nano fillers can effectively compensate for the structural defects of polymers.However,nano alumina has a porous structure,and after doping,there will be a phenomenon that the effect of improving the breakdown strength of insulating materials is not obvious.In response to the above problems,the surface modification of nano fillers has excellent improvement effects.This article mainly studies the modification effect of nano alumina from three aspects:surface modification of nano particles and establishment of paper preparation platform,analysis of modification effect and mechanism,and performance testing of aramid insulating paper.Based on molecular dynamics technology,the interfacial characteristics of nano Al2O3/meta aramid fibers before and after modification are analyzed.(1)Testing platform for volumetric conductivity,breakdown strength,and surface charge dissipation was established;Laboratory suitable platform for the preparation of aramid composite insulating paper was established.Based on the manufacturing process of industrial paperboard,the hot-pressing process parameters were optimized and designed,laying a foundation for subsequent experimental testing.(2)A method of modifying nano Al2O3 with dimethyldiallylammonium chloride(PDDA)was proposed.Aramid paper was prepared by modifying nano Al2O3 with different concentrations of PDDA and doping composite particles with different concentrations.FTIR,XRD,SEM,TEM,Zeta potential,and other means were used to characterize the physical and chemical properties of nanoparticles.It was found that PDDA caused the surface potential of Al2O3 to twist to a positive value without causing damage to the crystal form,increased surface roughness,and dispersed uniformly within the aramid paper.However,excessive concentration treatment would lead to the peeling of the modified layer.With the increase of the concentration of PDDA and nano-Al2O3,the breakdown strength and deep trap energy level of aramid paper first increase and then decrease,and the change trend of electrical conductivity is reversed.In addition,PDDA effectively improves the thermal stability of meta aramid paper and delays its thermal decomposition.The mechanical property test results showed that the elongation at break and tensile strength of aramid paper decreased significantly,while the decrease in Young’s modulus was small.(3)Due to the shortcomings of the modification effect of single polycation,the effect of double layer electrostatic coating modification on meta aramid paper was investigated.Nanosized Al2O3 particles with a core shell structure were prepared by using double layer electrostatic coating.Characterization result display HACC@STPP shell increases the surface roughness of nano-Al2O3,and the surface potential increases to+40.1mV.The insulation performance test results showed that the optimized modification improved the breakdown strength by 33%and decreased the electrical conductivity by 53%.After cross-linking,a good three-dimensional hydrogen bond structure is formed between the components inside the aramid paper,which endows the composite paper with excellent mechanical properties and thermal stability at low temperatures.At high temperatures,the formation of a carbon layer leads to a decrease in thermal stability.(4)The interfacial model of PMIA/Al2O3 was established and simulated using molecular dynamics to calculate the characteristic parameters of the system,such as hydrogen bonds,interfacial binding energy,and average azimuthal shift.The results showed that the change in the number and strength of hydrogen bonds in aramid paper caused by polycationic modification was the main reason that affected its insulation performance.Modifiers could increase the number and strength of hydrogen bonds in the system,thereby improving the interfacial bonding energy;However,the molecular segment motion of the system after the incorporation of two modifiers will increase with the increase of the doping ratio,resulting in a decline in the mechanical properties of aramid paper.