On the crosslinking temperature dependence of charge transport behavior in XLPE film deduced from surface potential decay measurements

Abstract

The effect of crosslinking temperature on charge transport behavior in crosslinked polyethylene (XLPE) film has been investigated by means of surface potential decay measurements. 200 μm-thick XLPE specimens were prepared by hot-molding low density polyethylene (LDPE) by adding dicumyl peroxide (DCP) as crosslinking agent and phenolic antioxidant with temperatures ranging from 150 to 180 °C. Surface potentials on corona-charged samples were monitored by using a Kelvin type probe equipped with an electrostatic voltmeter, based on which trap distribution, effective charge mobility and field dependent conductivity were estimated. Fourier Transform Infrared (FTIR) spectrum and Differential Scanning Calorimeter (DSC) analysis were employed to examine the change in chemical structure and crystal morphology of test samples. Results obtained show that the charge transport dynamics is cross-linking temperature and polarity dependent. With the rise of the crosslinking temperature, the mobility of positive charge increases monotonously from 1.05 × 10−16 m2V−1s−1 to 5.42 × 10−15 m2V−1s−1, whereas the mobility of negative charge shows a fall-and-rise tendency that a minimum value of 1 × 10−16 m2V−1s−1 appears at 160 °C. A single trap center for electron is observed at any test sample. However, as regards to hole, a double-trap-center feature tends to appear as the temperature exceeds 160 °C. Moreover, with the increase of the crosslinking temperature, the conductivity of sample becomes field dependent. It is suggested that the variation of charge transport behavior should be ascribed to the presence of by-products as well as the crystallinity change caused by the temperature.