EFFECT OF DYE CONCENTRATION DISTRIBUTION ON PHOTOFADING OF DISPERSE DYE IN CELLULOSE TRIACETATE

Cellulose triacetate films were dyed with C. I. Disperse Red 17 at 80°C and their photofading behavior was investigated. The dyed samples with various dye concentration distributions along their thicknesses were exposed to a high pressure mercury lamp. It was supposed that photofading rate is mainly influenced by the dye concentration distribution.To explain this correlation, the laminated-film exposure method was adopted. When the dye distribution is uniform, the time required to a certain fading percentage increases exponentially with film thickness. By extrapolation of the relation to zero thickness, the fading is assumed to occur in zero-order reaction at the surface of the sample. Then, the empirical formula for fading rate was derived. The formula suggests that the concentration-fading rate relation could be straight or curved depending on the parameters included.