Ageing evaluation of cable insulations subjected to radiation ageing: Application of principal component analyses to Fourier Transform Infra-Red and dielectric spectroscopy

The evolution of properties of crosslinked polyethylene (XLPE)-based insulating materials under radio-chemical ageing conditions is presented and discussed. In total, seven different polymer compounds were tested, characterised by an increasing quantity of additives, for example, antioxidants (AOs) and fillers as flame retardants. Samples were analysed using different testing techniques, that is, Fourier Transform Infra-Red and dielectric spectroscopy. This allowed a broad characterisation of the polymer, bringing to good correlations between the arising of new chemical groups caused by ageing and the modifications on the complex permittivity. Phenol-based AOs are found to be the most efficient in terms of protection against oxidation. On the contrary, flame retardants are concluded not to have any impact on the material ageing. Acquired data were then treated using the principal component analysis. The data treatment successfully distinguished the material composition (with and without additives) and the ageing environments. The results confirm the relevance of this analysis in understanding the impact of irradiation on the chemical and functional properties of the polymer materials studied.