ESTIMATION OF THE THICKNESS OF DIFFUSIONAL BOUNDARY LAYER BY ANALYZING RATE OF DYEING DATA AND BY MEANS OF MULTIPLE MEMBRANE LAYER METHOD

Abstract

Thickness of diffusional boundary layer (δD) on a cellulose membrane was estimated by means of multiple membrane layer method using non-ionic diffusants. The values of δD estimated under a good stirring were 0.9-2 and 0.4-0.6×10^-3cm at 80 and 30°C, respectively.
Rates of dyeing (or desorption) of non-ionic dyes on nylon 6 and polyester yarn were determined carefully. Comparison of rate of dyeing curves determined with those calculated by Hill's equation revealed the presence of a sorption delay in the dyeing. The delay decreased significantly as the rate of stirring of dyebath was increased. The delay was attributed to the resistance to transport of dye across the diffusional boundary layer surrounding the fiber.
Newman's equation, theoretical formula to express the rate of dyeing with the delay was used to calculate theoretical rate of dyeing curve. Boundary layer parameter (L) and diffusion coefficient of dye in fiber (D_f) were estimated by fitting the calculated curve to the experimental one. Values of δ_D estimated under a good stirring ranged in 1.3-4.4×10^-3cm. These results obtained revealed that the sorption delay due to diffusional boundary layer is inevitable in dyeing of fiber assembly even if a good stirring is made, particularly for the dyes with high affinity or large D_f.
Effect of temperature on the barrier action of diffusional boundary layer is discussed briefly.