Analysis of fading mechanism of salix integra dyed with reactive dye under ultraviolet irradiation by tri-step infrared spectroscopy

Abstract Under ultraviolet (UV) light, the salix integra will be faded after being dyed with reactive dyes. In order to study the chemical change in reactive dye on the dyed salix integra during the process of UV light, tri-step infrared spectroscopy is used to analyze the reactive dyes with different UV aging time. The results showed that the change in dye functional groups became more apparent when the UV aging time was increasing. The generation, disappearance or intensity change in peaks at 3432 cm−1, 2918 cm−1, 1632 cm−1, 1563 cm−1, 1501 cm−1, 1398 cm−1 and other wavelengths, which indicated that the unsaturated bonds of azo group, fused ring and cyanyl group in dye molecules were broken or isomerized. With the internal groups of reactive dyes experience electron transition and photooxidation under UV irradiation, the molecular structure will be isomerized and the unsaturated groups become broken simultaneously, which makes the color fade or even disappear.