Polyvinylidene fluoride dopant as voltage stabilizer for improving high-voltage insulation properties of polypropylene

Various additives ranging from inorganic nanoparticles to organic additives have been suggested to improve the insulation performance of polymeric materials for high-voltage engineering applications. Herein, we present a simple method for doping fluorine into a polypropylene (PP) matrix by melt-blending of isotactic PP (iPP) with a small amount of polyvinylidene fluoride (PVDF) as a thermoplastic voltage stabilizer (TVS). During melt-mixing, the PVDF TVS, which is immiscible with PP, is gradually split into smaller domains within the iPP matrix and was finely distributed, especially at a low PVDF content. The well-distributed PVDF acted as a nucleating agent for the facile crystallization of PP molecules, thus increasing the crystallization temperature ( T c ) and decreasing the spherulite size. We found that the direct current (DC) breakdown strength (BDS) values of the PVDF-doped iPP increased by 110% and 149% at 20 and 110°C, respectively, compared to those of the pristine PP. We hypothesize that the presence of fluorine sites as well as the increase in interfaces between spherulites with decreased size, without any significant degradation in the tensile strength and elongation at break below 1.0 phr of PVDF, were the reasons for our findings. Therefore, we anticipate that such PVDF-doped iPP is a potential candidate for high-voltage insulation systems.