Effect of Light Source on the Photodegradation of Certain Disperse Dyes

Abstract

Since outdoor weather conditions are highly variable, lightfastness determinations for dyed fabrics are generally made in controlled artificial environments. To determine how the light sources employed in such environments influenced the fading of the fabrics, certain disperse dyes in solution and on commercial synthetic fibers were photodegraded with light from monochromatic and polychromatic sources. Dyes were not degraded in liquid or polymeric media by light of wavelengths above 400 nm. Quantum yields for photodegradation of dyes by monochromatic light of wavelengths below 400 nm generally increased with decreasing wavelength; an apparent anomaly—the absence of dye photodegrada tion on polyester fabric with 254-nm radiation—was due to the screening effect of the polymer. Polychromatic irradiation of azo, anthraquinone, and methine dyes on commercial synthetic fibers resulted in dye degradation rates which were generally consistent with the fraction of short-wavelength emission of the light sources employed. Results from this work show almost any 280- to 700-nm light source is suitable for the division of dyes into 3 or 4 stability groups; however, since light absorption by dye, polymer and delusterant affects degradation rates, only a light source whose spectral energy distribution closely approximates that of sunlight can accurately simulate the dye degradation by outdoor exposure.