Influence of oxidation on space charge dynamics in DC aged low-density polyethylene

In this study, low-density polyethylene (LDPE) samples were aged under different oxygen concentration (0, 20%, and 50%). The ageing was implemented with an average external DC electric field of 50 kV/mm at 40 °C for 1000 h. It was found that augmentation of charge accumulation and suppression of charge dissipation were enhanced with increasing of oxygen concentration. The capture capability of trap sites got stronger with higher oxygen contents, which could be attributed to oxidation product newly generated during DC ageing. These trap sites acted as trap centers to capture the injected carrier while it was on the way towards the opposite electrode and decrease the apparent mobility. FTIR absorption spectra showed that new elements between 1680 and 1750 cm^?1 corresponding to ketone and aldehyde occurred due to oxidation. The bipolar charge injection model was implemented to simulate space charge transport in aged LDPE samples. It was shown that more carriers were captured and the traps gradually filled up when the oxygen concentration in the ageing test increased. A higher oxygen concentration seemed to result in a deeper average trap depth, which increased the amount of trapped charge because it was not easy to detrap. These simulation result corresponded to the experimental measurement.