Dissolving and Regeneration of meta-Aramid Paper: Converting Loose Structure into Consolidated Networks with Enhanced Mechanical and Insulation Properties

Abstract

Aramid paper has been widely used in high-voltage motors and transformers due to its excellent insulation property and thermal durability. However, the smoothness and chemical inertness of aramid fibers lead to a loose structure (voids) of aramid paper, which limits its potential applications in harsh environments, such as high-frequency and high-voltage circuits. This work reports a simple and efficient method to improve the mechanical and insulation properties of meta-aramid paper via controllable dissolving and regeneration of aramid fibers. To obtain a dense and robust structure, the pristine meta-aramid paper was immersed in a dimethyl sulfoxide/potassium hydroxide (DMSO/KOH) mixture to make aramid fibers swelled and dissolved, followed by regeneration in water vapor, eventually generating densified aramid paper with fewer voids and enhanced insulation and mechanical performance. Optimum conditions resulted in aramid paper with the best comprehensive performance, and the tensile strength, Young’s modulus, and electrical breakdown strength of the consolidated aramid paper were 22.85 MPa, 0.72 GPa, and 15.3 kV/mm, respectively, which were significantly higher than those of the pristine aramid paper (12.53 MPa, 0.41 GPa, and 8.36 kV/mm). Meanwhile, such treatment did not cause any chemical structure change, and thus it still retained the excellent thermal resistance (T d > 430 °C) of aramid fibers. This simple method can effectively regulate the surface porosity and the mechanical and breakdown strength of aramid paper, as well as provide a generic method for postprocessing and enhancing aramid paper.

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

“…The interaction between molecular chains decreased, so that the crystal structure would be able to be formed by PMIA molecular chains. The enhanced hydrogen bonding induced by solvent was also beneficial to increase the cristallinity 15 . Generally speaking, the XRD patterns demonstrate that the structure of meta‐aramid paper was enhanced after coating salt‐free PMIA slurry on the paper.…”

“…One way is to regulate the structure of aramid paper. Tan and her colleagues 15 founded that the system of caustic potash/dimethylsulfoxide (KOH/DMSO) could be used to regulate the structure of paper via swelling and dissolving and in situ regeneration of the meta‐aramid fibers, then the tensile strength was increased from 12.53 to 22.85 MPa and the breakdown strength was increased by 1.83 times. Lu and his coworkers 16 also used poly(p‐phenylene terephthamide) (PPTA) nanofibers to manufacture PPTA nanopaper.…”

Mechanically Strong Electrically Insulated Nanopapers with High UV Resistance Derived from Aramid Nanofibers and Cellulose Nanofibrils

“…Upon the addition of CNFs, the resultant nanopapers still maintained good dielectric properties (Figure e and Table S4). Furthermore, the ANF/CNF-2 nanopaper had a highest dielectric strength of 53.42 kV mm –1 , which was significantly higher than those of the aramid paper (8.36 kV mm –1 ) and the pure ANF nanopaper (50.35 kV mm –1 ) . In addition, the dielectric strength of the pure ANF and ANF/CNF-2 nanopapers with different grammages were also measured (Figure f).…”

“…Furthermore, the ANF/CNF-2 nanopaper had a highest dielectric strength of 53.42 kV mm −1 , which was significantly higher than those of the aramid paper (8.36 kV mm −1 ) and the pure ANF nanopaper (50.35 kV mm −1 ). 63 In addition, the dielectric strength of the pure ANF and ANF/CNF-2 nanopapers with different grammages were also measured (Figure 6f). The dielectric strength of all of the pure ANF and ANF/CNF-2 nanopapers increased with the increase of grammage.…”

“…43 As shown in Figure 6g, the electric breakdown sites of the pure ANF and ANF/CNF-2 nanopapers had no district holes, which was different from the aramid paper. 63 For the pure ANF nanopapers, a large piece of fibrous layers was turned inside out and the high voltage destroyed their layered structure. By contrast, the ANF/CNF-2 nanopaper was more complete in structure, in which only a small piece of fibrous layers was uncovered and the layered structure was obvious.…”