Microspectrophotometric Study of Ozone Fading of Disperse Dyes in Nylon

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Abstract
The fading of disperse-dyed nylon by atmospheric ozone can pose a problem at high environmental temperatures and humidities. In attempting to devise ways to inhibit such fading, researchers have suggested that the reaction between ozone and dye occurs chiefly at the fiber surface—that ozone does not penetrate inward, but that the dye diffuses outward from the fiber interior due to the concentration gradient set up as surface dye is destroyed. This mechanism has been supported, though not proved, by observations that dye diffusion is also sensitive to humidity in such systems, that rates of dye loss due to ozone exposure correlate with dye desorption rates into water, and that dye loss, like dye diffusion, depends on the square root of time and on the size of the dye molecule. These findings were based on determinations of total dye content in fiber specimens; however, adapting the techniques of microspectro photometry to fibers, as described in this paper, makes it possible to observe directly the locus of dye destruction in the fiber and to determine the relative dye loss at selected locations, such as at the edge and center of a fiber cross section. The coefficient of diffusion of the dye within the fiber can also be evaluated using the micropho tometer. These capabilities have been applied to the ozone fading of nylon 6 dyed with C.I. Disperse Blue 3, and the experimental results do not correlate with a math ematical model based on the hypothesis of dye destruction exclusively at the fiber surface. On this basis it is postulated that, in addition to dye diffusion toward the fiber surface, ozone penetration into the fiber contributes substantially to the fading process.
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