Copper-catalyzed oxidation caused by copper-rich impurities in cross-linked polyethylene cable insulation

In this paper, the existence of copper-rich impurities in cross-linked polyethylene (XLPE) cable insulation was evidenced by means of thermal-oxidative ageing. It was deduced by the results of DSC tests that copper-rich impurities can lead to decreased melting temperature and crystallinity of XLPE during the thermal-oxidative ageing process. Meanwhile, some cracks in branch-type originating from these impurities, which can be regarded as the generation of increased free volume, were observed by SEM. These results might be induced by enhanced chains scission and crystalline disruption due to copper-rich impurities. It was proposed that these impurities work as potential catalysts in oxidation reaction, resulting in accelerated inhomogeneous deterioration of XLPE. In addition, the Oxidative Induction Time (OIT) of XLPE was measured and it was found that copper-catalyzed oxidation reaction occurs only if the antioxidant in XLPE is nearly exhausted.