Influence of UV radiation on dielectric absorption and dielectric strength of halloysite nanotubes filled polyethylene composites

This paper deals with the evaluation of the amount of filler influence and the ultraviolet (UV) radiation influence on selected dielectric properties of the innovative type of composites. These composites consist of a linear low-density polyethylene matrix and a clay filler (with different filling levels) that contains halloysite nanotubes (HNT) primarily. The intended application of tested composites in the field of electrical engineering is in insulating systems of power cables. Attention is paid to the analysis of the behaviour of composites in their charging, which is caused by the connection with the direct voltage source. The volume resistivity and polarization indexes are determined based on this analysis. Analysis of charging based on the measurement of the current, which flows through the sample under constant applied voltage, is supplemented with the short evaluation of the material behaviour after the disconnecting of the voltage source and after the electrode shorting when the material is discharged. Furthermore, the measurement of dielectric strength under an alternating electric field as another key parameter of electrical insulating materials is determined. Results of analyses of absorption and resorption processes and the dielectric strength measurement of materials in the delivered state prove a significant effect of the filler percentage in the composite. Subsequently, markedly different values of selected parameters because of material exposure to UV radiation are also determined. Observed changes in dielectric properties caused by UV irradiation are supported by the analysis of the chemical structure of materials via Fourier transform infrared spectroscopy