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 C_f of dyes on the film and the actual diffusivities D _{( C )} of the dyes (C_f - D _{( C )} relation) are determined from the profiles using Matano's method. For most dyes, C_f - 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 D_{P ( C )} of the P species decreases gradually with de creasing C_f , from Cf at the polymer surface (C_fsur ) to Cf corresponding two to three times the saturation value of Langmuir sorption (S). Below this C_f , D _{( C ) P} decreases rapidly with decreasing C_f. Actual diffusivity D_L(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 C_fsur to C_f corresponding to two to three times S, and then decrease rapidly with decreasing C_f. 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.