Determination of the Effects of Accelerated Ageing on the Dielectric Properties of LLDPE and LLDPE/HNT Composites

Composites based on a linear low-density polyethylene (LLDPE) and containing clay filler halloysite nanotubes (HNT) are perspective due to advantageous fire retardancy. This paper is focused on an impact assessment of an accelerated aging on dielectric properties of these composites (LLDPE/HNT), more specifically, accelerated aging by intensive ultraviolet (UV) radiation is taken into account. Evaluation of this type of aging is important in every practical situation when electrically insulating layers are exposed to sunlight. Composites were prepared with three different weight percentage of clay filler and pure LLDPE is used as the reference material. Samples were exposed to UV radiation for 50 h, 100 h, and 150 h. Emphasis is placed primarily on the characterization of changes in dielectric strength in a harmonic electric field and volume resistivity of tested materials. Furthermore, tested materials were also analyzed by broadband dielectric spectroscopy to describe an influence of the exposure to UV radiation on the frequency and temperature dependent relative permittivity. Detection of a minimal deterioration and, in some cases, even a slight improvement of selected dielectric parameters of LLDPE/HNT caused by UV radiation, is very positive. Results obtained by broadband dielectric spectroscopy prove changes of polarization processes in tested composites which occurred as an effect of UV irradiation.