Highly flexible, large scaled and electrical insulating polyimide composite paper with nanoscale polyimide fibers

Modern polyimide (PI) paper could not satisfy the stringent requirements of the mechanical reliability, dielectric property, and environment friendly preparation for modern electrical equipment. Herein, the PI fiber with the dense three-dimensional network structure was obtained by planar centrifugal with poly(amic acid) (PAA) as sourced solution. The PI composite paper was formed by sandwiching the PI fiber paper with two PI films. The formation process, microscopic morphology, mechanical properties, thermal stability and dielectric properties of the PI fiber paper and PI composite paper were studied and evaluated. The PI fiber paper composed by nano fibers showed the good mechanical properties (tensile strength up to 4.17 MPa), high thermal stability (main weight loss temperature at 500–520 °C), lower dielectric constant (0.78–0.95) than air, and breakdown strength (up to 8.22 kV/mm). Based on the excellent performance of the PI fiber paper, the PI composite paper had a breakdown strength at 20.18 kV/mm, which was much better than commercial organic electrical insulating paper. Additionally, the production of large scaled PI fiber paper and PI composite paper could be achieved continuously and environmentally.