Influence of additives on the dielectric strength of high-densitypolyethylene

In this study, we present the results of the influence of chemical additives (antioxidant and UV stabilizer) and pigments (titanium dioxide and carbon black) on the short-term dielectric breakdown test of high-density polyethylene (HDPE). These additives and pigments are commonly added to polyolefins, which are used as insulating material for medium voltage cables. The incorporation was performed in a single screw extruder and thin films specimens were obtained by hot compression from extruded materials. For the dielectric breakdown test, an automated system has been used. A voltage ramp of 500 V/s was applied to specimens immersed in a silicon oil bath at room temperature. The degree of crystallinity and chemical modification of the formulations were evaluated by X-ray diffraction and Fourier transform infrared (FTIR), respectively. The dielectric breakdown results have been analyzed by a Weibull distribution. The shape and scale parameters of this distribution have been obtained by a graphic and maximum likelihood method. These results showed that the carbon black is the component that affects the dielectric strength, that the β shape parameter from the graphic method can be used to evaluate additive mixing conditions, and that the weakest point for formation of the rupture channel is on the carbon black agglomerate