Abstract
Polypropylenes (PP) are a candidate to replace cross-linked polyethylene (XLPE) in medium voltage cables. This is due to its recyclability and potentially lower energy consumption during production. To prove to be an alternative, the PPs must meet the same requirements as for XLPE. The maximum service temperature for XLPE is 90 °C. The syndiotactic PP (sPP) was chosen for this study. sPP has a significantly higher melting temperature (∼130 °C) than for other alternatives, such as LDPE/MDPE, but softening and morphology changes during service could be challenging. Thin sPP discs were therefore subjected to 90 °C and also thermal cycling between 20 and 90 °C with heating and cooling rates of ±0.2 °C /min and ±3.5 °C /min. Pristine sPP has low conductivity, losses and good mechanical properties. The temperature treatment changed the mechanical and electrical properties slightly. The tensile strength was lowered and the melt peak changed, but the total crystallinity did not change (24–26 %). The dielectric losses increased by a factor 2.5 for thermally aged samples. The conductivity was low and almost unchanged compared to reference for samples subjected to temperature cycling. Heat treatment weakens the electrical and mechanical parameters