Influence of Irganox 1010 on Space Charge Behavior in iPP Thermal-Oxidative Ageing

The potential application of eco-friendly thermoplastic material - Polypropylene (PP) for high voltage direct current (HVDC) cable has attracted significant attention. However, a better understanding of the ageing effects of on the long-term performance of PP is needed for a reliable operation of a HVDC cable. Based on previous work on thermal ageing of neat PP, an antioxidant (AO) has been introduced to investigate its influence in PP thermal-oxidative ageing for a long potential service life (>40 years) under high temperature in this work. According to chemical changes characterized using Fourier-Transform Infrared (FTIR) spectroscopy, the AO is initially ready to react with oxygen on sample surface and subsequently progresses towards the bulk of the sample over time. The space charge dynamics were measured with the pulsed electroacoustic (PEA) technique. It has been found that hetero charge formed near the cathode would further increase after adding AO, but negative charge becomes dominant with continuous poling time. After thermal ageing experiments are completed, there is an obvious charge injection near the cathode. Combined with the positive charge movement caused by the AO, a resultant charge peak can be observed. We correlate this behavior with DC breakdown strength experiments, which show an increase at an early stage of the ageing process, before decreasing as a function of ageing time.