Highly Ductile Polypropylene Based Ternary Blends for High Voltage Insulation

ABSTRACT High voltage insulation materials must combine excellent dielectric and thermomechanical properties. Ternary blends based on isotactic polypropylene (PP) tend to feature a low electrical conductivity and high melting temperature but are usually characterized by a too low ductility. Here, it is shown that the cooling rate can be used to significantly improve the ductility without compromising the otherwise excellent property portfolio. Rapid cooling of ternary blends comprising PP, low‐density polyethylene (LDPE) and a polystyrene‐ b ‐(ethylene‐ co ‐butylene)‐ b ‐polystyrene (SEBS) elastomer is found to result in a material with an elongation at break above 500%, which is maintained even after prolonged annealing at up to 135°C. At the same time, the ternary blend continues to exhibit a high elastic modulus above the melting temperature of LDPE and a low direct‐current (DC) electrical conductivity of 0.7 × 10 −15  S m −1 at 70°C and an electric field of 30 kV mm −1 . Evidently, rapid cooling of PP‐based insulation materials can facilitate the preparation of highly ductile insulation materials.