Sorption isotherms and dyeing rates of purified disperse dyes on polyester microfibers (fineness of 0.25-1.0 denier) from water have been measured at 95°C. The isotherms are curved and well described in terms of the dual-mode sorption model: Nemst-type partitioning and Langmuir sorption are concurrently operative. The effect of a diffusional boundary layer on the dyeing rate is small under the conditions; the microfibers were dyed in the form of a bulky two-ply yarn in a well stirred bath. Dyeing rates of a commercial dye are also measured at 110 and 130°C. For dyeing of a 0.32d fiber at 130°C, the amount of dye sorbed by the fibers attains a maximum value at an early stage and then decreases gradually. This phenomenon is explained in terms of the aqueous solubility of very fine dye particles. The relation between dye sorption behavior and the fine structure of the microfibers is discussed.

SYNOPSISSorption isotherms of 2,4-&nitroaniline and three 4-amino-azobenzene derivatives ( nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual-mode sorption model, Nernst-type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystalline phase. Keywords: sorption isotherms of nonionic azo dyes from water on polyamide Nylon 6, sorption of nonionic azo dyes from aqueous solution by crystalline phase of Nylon 6 and sorption of nonionic azo dyes

Diffusion of 2,4‐dinitroaniline and three nonionic azo dyes in Nylon‐6 film was studied by analysis of the concentration‐distance curves (profiles) of penetrants in the polymer. Actual diffusivities D(c) of penetrants in polymer, diffusion coefficients as a function of the concentration Cf of penetrant in polymer, were calculated from the profile. It was found that D(c) is almost constant or decreases gradually with decreasing Cf in the range of high‐medium Cf but decreases appreciably with decreasing Cf at low Cf. The change in D(c) with Cf was explained in terms of the dual‐mode sorption‐diffusion model. The penetrants diffuse in the polymer as two distinct species, i.e., a dissolved species and an adsorbed species. The former is the penetrant taken up by the polymer by a partition mechanism (dissolved species) and the latter is that taken up by Langmuir sorption (adsorbed species). The actual diffusivity DP(c) of the dissolved species decreases with decreasing Cf. While the actual diffusivity DL(c) of the adsorbed species normally increases gradually with decreasing Cf. DP(c) is usually larger than DL(c). © 1993 John Wiley & Sons, Inc.