Some quantitative studies of light fading of adsorbed dyes. Part 1.—Changes of light absorption of non-ionic dyes on fading, and their relation to the fading mechanism

Abstract

Measurements have been made of the ratio of extinction of the short-wave (y) and the long-wave (x) band in the visible region of spectra of four non-ionic (disperse) dyes sorbed in films of cellulose acetates, nylon, and polyester. The changes in the ratio with dye concentration and also with fading on exposure to light at given concentrations have been measured. The results are consistent with the presence of dye particles in a range of small sizes; association of dye appears to occur during the dyeing process. The smaller sizes, probably molecularly disperse dye, predominate, especially in polyester, and these fade the most rapidly. The nature of the change in ratio with time of exposure suggests that dye molecules become more resistant to photochemical breakdown when associated together.