Structural characters of biaxially stretched polypropylene films and the relevant electrical insulating properties

Capacitor films from biaxially oriented polypropylene (BOPP) involve intensive external stress field, resulting in special crystallization and orientation characters. However, it still remains ambiguous on the relationship between crystallized morphology in BOPP bulk film and electric properties. In this work, two stretching modes, simultaneously biaxial stretching and sequentially biaxial stretching, were chosen to adjust film thickness, extended chain crystal content, fibrillar morphology, and orientation texture. Meanwhile, the working rules of these structural issues on electrical insulating properties were inspected. It reveals that extended chain crystals with thermal stability and isotropous fibrillated network favor to improved breakdown strength and lowered dielectric loss. These results offer good understanding on the processing-structure-property relation of polymer film dielectrics.