Hierarchical Sandwich‐Structured Polyarylate Nanofiber/Meta‐Aramid Nanocomposite With Robust Dielectric Strength, Mechanical Durability, and Environmental Stability

Meta‐aramid (PMIA) insulating paper contains micron‐scale pore defects that limit its dielectric strength and reliability under high electric field and power conditions. Inspired by a sandwich structure, this study employed self‐fabricated polyarylate (PAR) nanofiber membranes as outer layers and commercial aramid paper as the core to fabricate hierarchical PAR/PMIA/PAR nanocomposite insulating paper via a scalable hot‐pressing consolidation process. The high‐aspect‐ratio PAR nanofibers formed a dense interwoven network, reducing pore density and mitigating electrical weak points. During hot pressing, the reversible melting of PAR effectively sealed inter‐fiber and interfacial pores, while π–π conjugation and strong hydrogen bonding with PMIA fibers ensured robust interfacial adhesion, suppressing electric field distortion from charge accumulation. As a result, the nanocomposite achieved tensile and breakdown strengths of 97.406 MPa and 114.55 kV/mm, representing increases of 51.3% and 204.3% over commercial aramid paper. After thermal aging at 200°C and 24 h UV exposure, breakdown strengths remained at 62.89 and 71.57 kV/mm (vs. 24.62 and 27.30 kV/mm for commercial aramid paper). Even after 20 crumpling‐twisting cycles and 100 folding cycles, breakdown strengths exceeded 46.78 kV/mm, demonstrating outstanding durability and structural stability under extreme thermal, mechanical, and radiation conditions. Compatible with industrial wet‐laid papermaking and hot‐pressing, this work provides a realistic route toward scalable manufacturing of lightweight insulating papers for high‐power motors, transformers, and photovoltaic modules requiring long‐term dielectric reliability.