Poly(m‐phenylene isophalamide) coated meta‐aramid paper with enhanced mechanical and insulation properties

Abstract Meta‐aramid paper is widely used in transformers because of its perfect heat resistance and dielectric properties. However, the loose structure and the voids of meta‐aramid paper may lead to lower breakdown strength, which will limit the applications of the insulated paper in harsh environment. Accordingly, it is urgent to enhance the dielectric breakdown strength of meta‐aramid paper. This work reports a simple and effective way to increase the breakdown strength of meta‐aramid paper. The paper was coated with salt‐free poly(m‐phenylene isophalamide) (PMIA) slurry and the solid contents of PMIA slurry were 4%, 6%, 8%, and 10%, respectively. To obtain salt‐free PMIA slurry, the meta‐aramid spun fibers were dissolved in dimethylacetamide. After coating 10% PMIA slurry on meta‐aramid paper, the paper demonstrated the best comprehensive performance. The tensile strengths in the cross and machine direction reached 40.67 and 90.76 MPa, which were increased by 29.93% and 20.16% compared with pristine paper. Meanwhile, the dielectric breakdown strength was up to 42.75 kV/mm (the breakdown strength of pristine paper was only 16.41 kV/mm). Because no crosslinking agent and adhesive were used, the coated meta‐aramid paper still maintained excellent properties.