Effect of Thermally Induced Self-assembly of β Nucleating Agents on Space Charge in Isotactic Polypropylene

Phase behavior of semi-crystalline polymers is closely related to topological structure evolution of nucleating agents (NAs). In this study, thermally induced self-assembly of TMB-5 β-NAs was prepared and its effects on dielectric properties and space charge characteristics in isotactic polypropylene (iPP) samples were investigated. The results show that β-NAs self-assembled from point-like shape into fibril when the heat-treated temperature reached 240 °C, and into three-dimensional dendritic structure when reaching 280 °C. Dielectric loss tangent and conduction current decrease and then increase with the rise of heat-treated temperatures, while DC breakdown strength is opposite. Self-assembly characteristics and changes of β-crystal content have been analyzed by polarizing microscopy and X-ray diffraction patterns. Moreover, influence of thermally induced self-assembly of β-NAs on charge evolution and field distortion has been discussed as well. This study provides a new way to simultaneously enhance dielectric property and suppress space charge in iPP via tailoring the hierarchical structure of βNAs.