Impact of Crosslinking on the Dielectric Loss and Temperature Coefficient of Capacitance of Polyethylene

Crosslinked polyethylene is a common material for power cable insulation due to its low cost, mechanical stability, and insulating nature. However, the crosslinking process leaves behind byproducts that may compromise its utility. Here, the impact of crosslinking on the capacitance and dielectric loss of polyethylene samples is examined. Crosslinked and noncrosslinked samples exhibit similar dielectric loss values at room temperature. However, crosslinked samples are more insulating at 90 °C. We observe that the amount of peroxide added was not directly related to the electrical properties, but that crosslinking temperature and time are. These results imply that the morphology changes upon crosslinking are as important in controlling the conductivity and loss as any residual byproducts. It is also observed that the degassing at elevated temperatures in vacuum that is normally done to remove byproducts also benefited non-crosslinked films, supporting the argument that morphology changes due to the elevated temperatures used in degassing can cause a reduction of dielectric loss. Analysis of mechanical properties through the use of temperature coefficient of capacitance, used to approximate the linear thermal expansion coefficient, allowed for further analysis of the morphology. Crosslinked films expand more than non-crosslinked films, and their expansion is reduced with degassing. Both ambient and vacuum degassing aid in this, implying that recrystallization and byproduct removal combined lead to reductions in dielectric loss and thermal expansion in crosslinked polyethylene.