| High-performance aramid mica paper is the paper-based insulating material obtained by wet papermaking and hot pressing with aramid fiber and mica sheet as raw materials.It is widely used in electrical insulation,rail transit,new energy,defense industry,etc due to its excellent high temperature resistance,chemical stability,electrical insulation performance,mechanical properties,and flame retardancy.However,due to the large difference in physical properties between aramid fiber and mica and their strong surface inertia,the interfacial bonding of aramid mica paper is poor,resulting in lower mechanical properties and insulation properties,which limits its further application.Therefore,it is an urgent problem to improve the mechanical properties and insulation properties of aramid mica composite paper by improving the interfacial bonding.In this paper,the effects of multiple variables,hot pressing process and bridging effect on the properties of aramid mica paper were investigated.The paper uniformity,mechanical properties and insulation properties of aramid mica paper were promoted by improving the interfacial interaction between aramid fiber and mica.Firstly,the effects of several variables in the preparation process of aramid mica paper（the ratio of aramid fibrids to chopped fiber,PEO dosage,mica content and the particle size of mica）on the drainage rate,paper formation,mechanical strength and insulation performance of aramid mica paper were investigated.The results showed that when the ratio of fibrids and chopped fibers was 7:3,the dosage of PEO was 0.5 wt.%,the content of mica was 50 wt.%,and the particle size of mica was 120μm-150 μm,the comprehensive performance of aramid mica paper was the best.The filtration time was short（150 s）and the tensile index,interlayer bonding strength,volume resistivity and breakdown strength of aramid mica paper reached 13.82 N·m/g,117.8 J/m2,4.46×1015 Ω·cm and 10.48 kV/mm,respectively.At this time,the compact three-dimensional network structure was formed between aramid chopped fiber,precipitated fiber and mica.Therefore,aramid mica paper exhibited excellent properties of high Mechanical and insulation strength.However,due to the lack of hot pressing of aramid mica paper,there were still a large number of pore defects at the interface between aramid chopped fiber and mica,which make aramid mica paper vulnerable to stress concentration and fracture and avulnerable to electrical breakdown and failure as well.Secondly,the effects of hot pressing temperature,hot pressing pressure and hot pressing time on the crystalline structure,mechanical and insulation properties of aramid mica were investigated.The results showed that the crystallinity of the paper-based material increased after hot pressing,indicating that the hot pressing made the aramid mica paper structure become orderly and regular.Hot pressing temperature has the significant effect on the properties of aramid mica paper.With the increase of hot pressing temperature,the tensile index and interlayer bonding strength of aramid mica paper showed an upward trend.When the hot pressing temperature was 240℃,they reached 26.89 N·m/g and 276.8 J/m2,respectively,which were 53.17 % and 58.24 % higher than those of unpressed paper.The breakdown strength of aramid mica paper increased first and then decreased with the increase of hot pressing temperature.When the hot pressing temperature is210℃,the breakdown strength is the highest,which is 9.53 kV/mm.When the hot pressing temperature was 210℃,the hot pressing pressure was 12 MPa and the hot pressing time was 10 min,the tensile index,interlayer bonding strength,volume resistivity and breakdown strength of aramid mica paper reached 25.84N·m/g,249.28 J/m2,6.82×1015 Ω·cm and 11.45 kV/mm,respectively,which were51.26 %,53.63 %,87.36 % and 29.51 % higher than those of unhot pressed paper.Therefore,the structure of aramid mica paper can be significantly improved by hot pressing and the interfacial bonding of paper-based materials can be improved so that the mechanical and insulation properties of aramid mica paper can be improved.Finally,methyl cellulose（MC）was introduced in the paper-based material as a bridging agent to explore the effects of MC addition and hot pressing on the properties of aramid mica paper.The mechanism of MC on the interfacial bonding of aramid mica paper was discussed.Study results showed that the addition of MC synergistic hot pressing can significantly improve the interfacial bonding aramid mica paper to enhance the mechanical strength and insulation strength of paper-based materials.When the adding amount of MC was 20 wt %,the hot pressing temperature was 180℃,aramid mica paper showed the best mechanical properties and insulation properties.The tensile index,interlayer bonding strength and breakdown strength reached 35.18 N-m/g,278.72 J/m2 and 30.40 kV/mm,respectively,which were 9.01 %,11.14 % and 27.64 % higher than those of paperbased materials without MC.The bridging effect of MC and hot pressing synergistically improved the interfacial bonding between aramid fiber and mica,reduced the pore defects of paper-based materials,and further enhanced the mechanical properties and insulation properties of aramid mica paper. |
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