Effect of Blending Modification on the Mechanical and Dielectric Properties of Polypropylene for Environment-friendly Cable Insulation

Polypropylene (PP) has the good potential to be used in insulation material of environment-friendly cable due to its high temperature stability and excellent recyclability. However, the high stiffness and brittleness of PP are the main reasons for its restriction of application in cable insulation. Therefore, how to improve the mechanical properties of PP and maintain its excellent thermal and dielectric performances have been research focus in recent years. In this paper, polyolefin elastomer (POE), styrene-ethylene butylene-styrene triblock copolymer (SEBS) and atactic PP (aPP) were introduced into isotactic PP (iPP) by blending with the mass ratio of 2:3, respectively. The mechanical properties of the three iPP-based blends were characterized by tensile test. Then, the dielectric and AC breakdown characteristics were measured respectively. Furthermore, the melting and crystallization processes were characterized by differential scanning calorimetry (DSC). Results demonstrate that the iPP/SEBS blend shows the best mechanical properties with the tensile strength and elongation at break increasing by 48.5% and 273.4% respectively to the iPP. In addition, iPP/SEBS blend has the highest AC breakdown strength of 54.8kV/mm among the three blends, only 5.2% lower than that of iPP. The DSC results reveal that the melting temperature of three blends has no obvious difference, while the crystallinity of iPP/SEBS is slightly higher than that of iPP/POE and iPP/aPP. The improved mechanical properties of iPP/SEBS is mainly due to the effective stress dispersion of SEBS deformation when subjected to external force, and the highest breakdown strength of iPP/SEBS is attributed to the high crystallinity.