Crystal Form Affecting DC Conductivity of Polybutene and Its Copolymer Insulation

This article focuses on the DC conductivity mechanisms of isotactic polybutene (iPB) and polybutene-block-propylene copolymer (PBA) varying with crystal form at different temperatures (30, 50, 70, and 90 °C) and electric fields (1-70 kV/mm). The crystal form transformation of polybutene insulation is investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results indicate that at low electric fields, polybutene exhibits mainly ohmic conductivity. As the electric field increases, DC conductivity is influenced by the traps inside the insulation and is mainly determined by the combined effect of space charge limited current (SCLC), hopping conduction, and Schottky effect. However, the Schottky effect is only significant at temperatures above 70 °C and electric field above 35 kV/mm. Besides, for PBA, the addition of 3 wt% propylene segments and the transformation of polybutene from form Ⅱ to form Ⅰ can both expand the range of the polybutene ohmic region and increase the Schottky injection threshold field, allowing polybutene to exhibit superior DC conductivity characteristics.