Design of Sandwich‐Structured Flexible Meta‐Aramid Composite Paper With Enhanced Breakdown Strength Over a Wide Temperature Range

Conventional meta‐aramid paper, typically composed of poly( m ‐phenylenediamine isophthalamide) (PMIA) chopped fibers and fibrids, is inherently limited by high internal porosity and surface roughness, which severely restricts its reliability in high electric fields. Herein, interface engineering was employed to fabricate sandwich‐structured composite papers via an impregnation strategy by combining poly(methyl methacrylate) (PMMA) with etched meta‐aramid paper. During this process, PMMA not only infiltrates the internal pores but also forms encapsulating surface layers on both sides of meta‐aramid paper, establishing a dense, robust architecture. Driven by the synergistic effects of multiple interfacial structures and hydrogen bonds between PMMA and meta‐aramid paper, the resulting composite papers exhibit significantly enhanced tensile strength across a wide temperature range. Notably, the breakdown strength of PMMA/meta‐aramid/PMMA composite paper reaches 57.1 MV/m at room temperature (RT) and remains at 46.9 MV/m at 100°C, representing remarkable 2.1‐ and 1.8‐fold improvements compared to pristine meta‐aramid paper. Furthermore, density functional theory (DFT) calculations and finite element simulations elucidate that the wide‐bandgap PMMA effectively inhibits electron transition, while the PMMA layers significantly redistribute electric field within the meta‐aramid paper. Consequently, this work offers a novel strategy for developing high‐performance meta‐aramid insulating materials tailored for demanding wide‐temperature applications.