THE INVESTIGATION ON THE DIFFUSION COEFFICIENT OF ACID DYE IN NYLON 6 FILM AT VARIOUS pH'S

Abstract

The diffusion of an acid dye (Acid Red 18) into Nylon 6 film from an infinite dyebath at various pH's was studied by means of the film roll method. The dyeing mechanism of Nylon 6 film with the acid dye varied with the pH of the dyebath: at pH lower than about 3.0 the adsorption of dye anions took place both on charged end amino groups, and amide groups, simultaneously, in the pH range from about 3.5 to 5.0 only on charged amino groups and at pH higher than about 6.0 on non-ionic sites. From the distribution of the dye through the film, the diffusion coefficients of the dye in the film corresponding to the adsorption on amino-, amide groups or nonionic sites were calculated, respectively, using some appropriate assumptions. The main assumption is that α, the fraction of end amino groups occupied by dye anions on the film surface, is equal to unit. This assumption is reasonable in this experiment.The results obtained in this paper are as follows:(a) The diffusion coefficient of the dye adsorped on charged amino groups is influenced by the variation in pH of the dyebath, that is, it increases with decreasing pH.(b) The diffusion coefficient of the dye adsorped on charged amide groups increases with decreasing pH. The dye anion interacting with charged amide groups can diffuse more quickly in the film than that interacting with charged amino groups.(c) The diffusion coefficient of the dye adsorped on non-ionic site is independent of the pH of the dyebath. This diffusion can occur most quickly among the three.