Effects of Annealing Treatment on Breakdown Properties of Eco-Friendly Polypropylene Copolymer for Cable Insulation

The recyclable polypropylene (PP) insulation has garnered increasing attention, making it a potential replacement for the commonly used cross-linked polyethylene (XLPE) insulation. However, the decline in electrical properties is always induced due to the elastomers that are introduced to achieve the improvement in toughness at low temperatures. In order to tackle the issue, in this paper, the annealing treatment at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$80^{\circ}\mathrm{C}$</tex> was performed to further improve the breakdown properties of impact polypropylene copolymer (IPC). It was found that the AC breakdown strength can be enhanced from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$130.8\text{kV}/\text{mm}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$148.9\text{kV}/\text{mm}$</tex> by the treatment of 36 h. Further results indicated that the annealing treatment with appropriate time can increase the crystallinity from 24.9% to 29.6%, restricting the movement of chains in the amorphous region. Additionally, more deep traps with higher energy level were introduced by annealing, limiting the migration of carriers and improving the breakdown properties. The results of this paper can provide a theoretical basis for the post-treatment process design of PP-based insulated cable.