Pathways for Dye Diffusion in Wool Fibers

The most prominent view of the diffusion mechanism of dyes into wool fibers assumes that the molecules primarily enter the fiber in a fast process along the cell membrane complex (CMC), that is, by an intercellular mechanism. From the CMC, they are subsequently distributed in a slower process throughout the other morphological components according to their respective diffusion coefficients and dye affinities. This view, referred to here as the CMC-diffusion model, is based on investigations of the diffusion performance of heavy metal complex and fluorescent dyes under anhydrous and aqueous conditions. An evaluation of various key aspects of the evidence for this model suggests that, due to differences in the glass transition and fluorescence quenching performance of the various morphological components in a wool fiber, there is, in fact, little evidence to support the CMC-diffusion model. Instead, the evidence supports the alternative, more general view that under normal dyeing conditions, diffusion proceeds primarily by means of all the nonkeratinous components of the wool fiber according to a restricted transcellular diffusion mechanism.