Double-network cellulose-reinforced PBO insulating paper with synergistic flame-retardancy, mechanical robustness, and low dielectric constant

Insulating paper is essential for the reliable operation of electronic and electrical equipment, yet achieving both high strength and flame retardancy remains challenging. Poly(p-phenylene benzobisoxazole) nanofibrils (PNFs) possess inherent excellent thermal stability and flame retardancy, making them highly promising for applications in the electronic and electrical fields. In this work, cellulose acetate (CA) is innovatively introduced between PNFs to construct a double-network structure. High-performance CA-PNF insulating paper is then fabricated via sol–gel processing combined with hot-press molding. Owing to the strong hydrogen-bond interactions between CA and PNFs, the resulting CA-PNF insulating paper demonstrates excellent electrical insulation, high mechanical strength. The CA-PNF insulating paper with 10 wt% CA shows the highest volume resistivity (8.1 ⨯ 10 14 Ω·cm) and breakdown strength (131.7 kV/mm). It also exhibits a relatively low dielectric constant ( ε ) and high wave-transparent rate (| T | 2 ). The CA-PNF insulating paper with 15 wt% CA exhibits the highest performance. Its tensile strength and toughness are 279.4 MPa and 28.1 MJ·m −3 , representing improvements of 51.5% and 150.3% over the PNF insulating paper, respectively. In addition, it also shows excellent thermal conductivity, and flame retardancy, with high LOI and rapid self-extinguishing behavior. These features highlight its potential for applications in communication devices, high-performance transformers, and new-energy electric vehicles.