Effects of Temperature-Induced Crystalline Phase Transition on the Space Charge Characteristics of Isotactic Polypropylene

Isotactic polypropylene (iPP), especially its <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> - crystal form, has demonstrated outstanding advantages in terms of electrical insulation properties. However, under certain conditions, the metastable <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex>-crystal form may transform into the more stable <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha$</tex>-crystal form, which could affect the insulating properties of iPP and potentially threaten the safe and reliable operation of power cables. This study focuses on the temperature-induced crystalline phase transition behavior of iPP, first exploring the specific conditions for temperature-induced phase transition. Based on the determined conditions for temperature-induced phase transition, further research was conducted on the performance changes of iPP after constant-temperature phase transition treatment. The research found that the higher the temperature of the constant-temperature phase transition treatment, the more complete the transition from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> phase to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha$</tex> phase, with an increase in melting temperature and no significant impact on crystalline properties. Under a field of -30 kV/mm, with the increase of constant-temperature, the space charge injection amount of iPP increased, as did the field distortion rate. The data and analysis obtained from this study provide reference information for the regulation of the crystal form of iPP and its impact on electrical insulation properties.