Effect of Antioxidants on Crystalline Structure of Crosslinked Polyethylene for Power Cables

The addition of antioxidants to high voltage crosslinked polyethylene (XLPE) cable insulation can not only improve its processing properties by inhibiting premature crosslinking, but also slow down the aging of the cable in operation. Moreover, the introduction of antioxidants also affects the crystalline structure of the insulating materials. Investigations of the effect of antioxidants on crystalline morphology are instructive to reveal the relationship between formulation and the electrical properties of the insulations. In this paper, four typical antioxidants are used to prepare crosslinkable and crosslinked polyethylene samples with different formulations. The crystalline morphology of the samples is observed using scanning electron microscopy (SEM) and the crystalline parameters are calculated by X-ray diffraction (XRD) spectra. The results show that for cross-linkable polyethylene, the introduction of antioxidants increases nucleation densities and diminishes the size of aggregates. Different types of antioxidants bring about different crystalline morphology. The morphology evolves further after crosslinking process. Crosslinking network inhibits the development of spherulites resulting in sheaf-like lamellar structures. Also, the better the antioxidation property, the lower the crosslinking degree of the XLPE samples, so that the crystallization is more well-developed. This study illuminates the influence of additives on the crystalline structure of low-density polyethylene and XLPE, which is of significance for the cable insulation formulation design and insulation performance enhancement.