Effect of ultraviolet radiation aging on the optical properties of Si-XLPE insulation

This paper highlights the effect of accelerated ultraviolet (UV) radiation on the optical properties of silane cross-linked polyethylene (Si-XLPE) widely used in the manufacturing of photovoltaic system connection cables. Ultravioletlight is one of the main causes of degradation affecting the lifespan of polymers and leading to modifications of their optical properties. In this work, firstly we have conducted cyclic accelerated UV radiation aging in the QUV aging test cell on the Si-XLPE samples. UVB-313 fluorescent lamps were used to generate an irradiance of 1 W m −2 at a temperature of 50 °C. The total aging time was 288 h. UV–visible spectroscopy was used to characterize the induced changes in the optical and dielectric properties by the UV radiation aging. From the obtained results, it was highlighted that Si-XLPE presents many absorption bands originating from the electronic vibrations of conjugated double bands. In addition, it was found that the absorption edge, the average number of carbon atoms and the Urbach energy increase and then decrease with increasing aging time, however, the indirect and direct band gaps decrease and then increase. The overall behavior may be related to the creation of defects (double bonds, cross-linking points, unsaturated groups…) in Si-XLPE by UV radiation aging. The optical dielectric constant and optical conductivity were also measured, and the results showed that the dielectric constant and optical conductivity present a single relaxation mode according to wavelength variation and the maximum is notably dependent on the UV radiation aging time.