PHOTOOXIDATION AND PHOTOFADING OF DYED NYLON-6,6 FILM - INFLUENCE OF ACID DYE CONCENTRATION AND RELATIONSHIP WITH LUMINESCENT SPECIES

The effect of concentration on the photofading rates of two yellow azo acid dyes (C.I. Acid Yellow 135 and C.I. Acid Brown 226) has been examined in nylon-6,6 film and compared with the influence of the dyes on the photochemical oxidation of the polymer using u.v. absorption and viscometric analysis. The data have been related to the concentration of the fluorescent and phosphorescent unsaturated carbonyl chromophores in the polymer. For both dyes, the rate of photooxidation of the polymer was found to increase with decreasing dye concentration with the rate of dye fading exhibiting a similar but slower trend. In both cases, the dyes were more stable than the polymer with C. I. Acid Brown 226 exhibiting no significant fading above 0.2% w/w. The dye fading and polymer stability results show a close correlation with the ability of the dyes to quench the luminescent chromophores in the polymer. The ability of the dyes to quench the phosphorescent species was found to be most significant as indicated by the correlation coefficients. This result confirms previous findings on the importance of triplet energy transfer in the stabilization of acid dyed nylon-6,6 polymer, with the metal complex types being the most effective.