Lightweight, low dielectric and heat-resistant polyimide fiber bulkpaper developed via alkali activated strategies for advanced insulation

With the prosperity of aviation, aerospace, and military equipment, critical requirements asked for insulating materials, which not only seek outstanding insulation, and low dielectric but also put particular emphasis on lightweight and heat resistance features. Herein, to enhance polyimide (PI) fibers bulkpaper, surface modification strategies were proposed and researched. Specifically, the hydrolysis effects of NaOH/DMAc and NaOH/H2O systems on PI fibers and PI fibers bulkpaper were investigated. The results indicated that the NaOH/DMAc system possessed more effective activation, which was proved by the contents of O elements and CO groups. Besides, the PI fibers bulkpaper derived from alkali-activated PI chopped fiber was developed through a wet-forming route, whose exhibited excellent performance with a density of 0.26 g/cm3, stress strength of 15.83 MPa, interlayer bonding strength of 293.47 J/m2, and electrical breakdown strength of 6.88 kV/mm. In addition, the bulkpaper exhibited low dielectric constant and dielectric loss of 1.37 and 0.0043 (at 106 Hz), respectively. The activation strategies provided a feasible path for advanced bulkpaper enhancement.