Influence of modifying on the dielectric and conductive properties of polyimide composite

In recent years, many efforts have been done to prevent circuit board used in space environment from deep dielectric charging, which is a serious threat to operational spacecraft. In this paper, in order to obtain a kind of dielectric material that can release harmful charges rapidly under high electric field, a kind of semi-conductive metallic oxide granules of different diameters ranges from nano to micron were used to modify polyimide resin with glass fibers. Here, 4 kinds of polyimide resin with non-alkalis glass fiber, including the original, micro-filler, nano-filler, and micro/nano-filler modified samples, and a kind of polyimide resin with glass fibers that contained small amount of alkalis were prepared, and the dielectric properties and nonlinear conductivity property of all the samples were measured. The results shows that the size of inorganic metallic oxide granules has little influence on materials' dielectric properties; in contrast, compared with the other sizes granules, semi-conductive granules of micrometer scale, can cause an obvious increase of the materials' volume conductivity. Furthermore, compared with non-alkalis glass fiber samples, the threshold electric field of nonlinear conductivity of the composites strengthened by the glass fibers with small amount of alkalis decreases obviously. The investigation indicates that different modifying methods lead to different charge transfer mechanism on the interface of polyimide resin and glass fibers.