Lightfastness of Reactive Dyes

Abstract

The lightfastness of a 2, 3-dichloroquinoxaline-6-carbonyl-amino fiber-reactive dye in cotton has been investigated. Fading has been measured as a function of exposure time by (a) reflectance measurements and (b) by determining the actual dye concentration in the faded fabric dissolved in 70% sulfuric acid. Lightfastness is shown to depend upon the location of the dye in the fabric and, in turn, upon the dyeing conditions. Fading is independent of the number (one or two) of reactive chlorines displaced at the quinoxaline nucleus. The shape of the fading curves depends upon the dye distribution in the fabric and the method of measurement. Fading curves of the dye which has completely penetrated the fabric resemble either zero- or first-order kinetics. Incomplete dye diffusion during dyeing causes considerable non lineariy. The results suggest, in contrast to conclusions by Giles and coworkers, that the shape of fading curves is not a valid indication of dye aggregation.