Effects of Different Ethylene-based Copolymers on the Structure and Dielectric Properties of Polypropylene Blends

In the power cable insulation industry, polypropylene (PP) has shown great potential in the development of new power cable insulation materials because of its higher melting temperatures, excellent dielectric properties, and recyclability. However, its mechanical stiffness restricts its use in power cable insulation. In this paper, PP/copolymer blends with different types of ethylene-based copolymers, namely, ethylene-propylene-diene monomer (EPDM) and ethylene-octene copolymer (EOC), at a 10 wt% copolymer content, prepared using a melt blending method, are studied. The effects of the copolymers on the PP/copolymer blends are reported through microstructure, dielectric response, and breakdown analyses. The results show that both the copolymers disperse well in the PP matrix, but each copolymer results in different dielectric effects of PP. Remarkably, the breakdown strength of both the PP/copolymer blends is better than the conventional cross-linked polyethylene (XLPE), even though the breakdown values are lower compared to that of the pure PP. Notably, with the presence of elastomer in PP, the elongation of break for PP improved up to 400% for both PP/EPDM and PP/EOC blends. This indicates that PP blended with ethylene-based copolymers, especially PP/EOC blends, can be a suitable candidate to replace traditional power cable insulation materials.