Diffusion of Disperse Dyes on Nylon 6

Abstract

The diffusion behavior of nine azo and two anthraquinone dyes on nylon 6 film is studied by analyzing dye distribution profiles. Relations between concentrations Cf of dyes on the film and the actual diffusivities D( C) of the dyes ( Cf - D ( C) relation) are determined from the profiles using Matano's method. For most dyes, Cf - D( C) relations at 80-90°C are explained well in terms of the dual-mode sorption-diffusion model in which the dye penetrates the polymer as two distinct species: dye taken up by Nernst- type partitioning (P species) and by Langmuir sorption with one class of sorption site (L species). The actual diffusivity DP( C ) of the P species decreases gradually with de creasing Cf, from Cf at the polymer surface ( Cfsur) to Cf corresponding two to three times the saturation value of Langmuir sorption ( S). Below this Cf, D( C ) P decreases rapidly with decreasing Cf. Actual diffusivity DL(C) of the L species usually increases gradually with decreasing Cf. As a result, D ( C) values of disperse dyes are almost constant or gradually increase (or decrease) with decreasing Cf, from Cfsur to Cf corresponding to two to three times S, and then decrease rapidly with decreasing Cf. For diffusion of some dyes at low temperatures (<60°C), the C f - D( C) relations may be explained much more accurately by considering that all three sorption modes operate concur rently, i.e., Nernst-type partitioning and two classes of Langmuir sorption, one with high affinity and small S, and other with low affinity and large S.