Preparation and Corona Resistant of Polyimide/TiO_2 Nanocomposite Films

The polyimide(PI)/TiO2 composite films with different component were prepared by in-situ dispersion polymerization. Thickness of the obtained films is about 50 μm. The characterization results show that diameter of spherical TiO2 in the films is about 100 nm and the size of the lamellar polyimide is about 2 μm ×1 μm. With the increase of the TiO2 content, electrical breakdown strength increases firstly and then decreases, while the values of permittivity, dielectric loss, corona resistant lifetime increase. Under the electric field of 40 kV/mm, corona resistant lifetime of pure PI is about 3 h, while the lifetime of composite film with 20wt% TiO2 is about 25 h. TiO2 has a high performance in corona resistance forming interphase with polymer and changing the trapping levels of material, facilitating diffusion of space charge and transmission of heat in material. A large of TiO2 particles can form discharge blocking layer on the surface of films and reduce internal erosion by partial discharge. Therefore, the corona resistant ability of nanocomposite films is significantly improved.