Trap Distribution and Dielectric Breakdown of Isotactic Polypropylene/Propylene Based Elastomer With Improved Flexibility for DC Cable Insulation

In this paper, we report on electrical and mechanical properties of isotactic polypropylene (PP) blended with polyolefin elastomer (POE) and propylene-based elastomer (PBE). Carrier trap distribution of the samples was estimated by isothermal surface potential decay measurement, while dc breakdown strength was measured through a pair of semicircle electrodes. Elongation at break and tensile strength were obtained to examine the variation in mechanical property of PP caused by the addition of elastomers. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) have been employed to assist the understanding of morphology of the blends, thermal properties, and mechanical properties. Obtained results have indicated that with the increase of the elastomer content from 0 to 30 wt%, the trap depth appeared to be shallower and the dc breakdown strength tended to be reduced for both PP/PBE and PP/POE samples. Compared with PP/POE blend, PP/PBE blend had deeper trap depth, which should be responsible for its higher dc breakdown strength. In addition, PP/PBE blend has presented a better performance in elongation at break and tensile strength measurement. With the growth of the elastomer content, the crystallinity of the blends appeared to decrease, whereas the melting and the crystallization temperatures did not change remarkably. The SEM inspections and DMA results revealed better compatibility between PP and PBE compared with that between PP and POE, which should be the reason for the better electrical and mechanical properties of PP/PBE blend. The blend of PBE with low content could result in remarkably improved flexibility of PP with acceptable electrical strength for dc cable insulation.