Influence of ultraviolet aging on the structure,mechanical and gas permeability properties of hydrogenated nitrile butadiene rubber

The effect of ultraviolet (UV) radiation on the structure and performance of hydrogenated nitrile butadiene rubber (HNBR) was studied in this paper. The HNBR was exposed to UV radiation for various durations (0, 7, 14, 21 and 28 days). The Fourier transform infrared spectroscopy (FTIR) results demonstrated that the surface molecular structures were oxidized to generate oxygenated species under UV radiation. The oxidative degree enhanced with the increase of aging time, resulting in thicker and denser cracks on the surface. The plausible aging mechanism of HNBR was suggested. The free volume of HNBR before and after UV aging was characterized by positron annihilation lifetime spectroscopy (PALS) and their cross-linking density, compression set, mechanical and gas permeability properties were also analyzed. In the first 14 days of UV irradiation, the dominant chain-scission reaction led to a decrease in cross-linking density of HNBR, resulting in the enhancement of free volume and thereby the increase of gas permeability. When the aging time was longer than 14 days, cross-linking reaction played a leading role and the free volume decreased, thus causing the reduction of gas permeability. As the aging time increased, the glass transition temperature (T_g), tensile strength and storage modulus of HNBR initially reduced and then increased, which was in agreement with the changing trend of cross-linking density.