Variation in Charge Transport Behavior of Polypropylene/Elastomer Blends Exposed to Thermal Cycling

Polypropylene (PP) has great electrical insulation performance and is easy to recycle, which makes it a promising candidate for high voltage direct current (HVDC) cable insulation. The cable in real operation has to face both high and low temperatures which are originated from the change in current carrying capacity of cable conductor, which may bring variation in material structure of cable insulation thus influencing the electrical performance. In this work, isotactic polypropylene blended with different content polypropylene based elastomer (PBE) and ethylene octane elastomer (EOC) were prepared as test samples. The influence of the thermal cycling time on the micro-structure and charge trans port manner of the blend samples were discussed. Obtained results indicated that similar changes appeared on PP/PBE and PP/EOC blends with the increase of thermal cycling times. Only a small part of the PP/elastomer blends was oxidized and less carbonyl group was generated. The diameter of the PP/elastomer blends crystallization became smaller and a small amount of the shish-kebab crystal was formed, while the boundaries of spherulites and amorphous region were increased. The trap density and the trap depth increased, the carrier mobility increased, and DC breakdown strength dramatically decreased. It is suggested that the charge transport in PP/elastomer blends is accelerated due to the significant increase of shallow carrier trap caused by the thermal cycling aging.