Abstract
Amilan (Nylon 6, Toyo Rayon Co.) was dyed by the so-called changing dyebath method which is a variation of the infinite dyebath method, adjusting the pH in the dyebath with such a concentration of phosphate buffer solution that the salt anion did not affect the dye uptake on the fibre. In this method the dyebath was changed frequently with fresh dye liquor having the same composition as the initial one as the dyeing proceeds, repeating this process until the equilibrium was attained. By the above method we are to obtain the dyeings which are in equilibrium with any arbitrary concentration of the dyebath. In the present experiment, however, the dyebath concentration was kept in the pH range 2-8. We have calculated the affinity of dye acid by the application of Gilbert-Rideal equation to our results.
The affinities of 14 acid azodyes, which were determined by this method at 59°C, were compared with those measured by usual dye acid adsorption method. This new method was found to be useful for the determination of affinity, since it shortenes the time of attaining to the dyeing equilibrium to 1/5_??_1/3 times of that required in the case of dye acid adsorption method, besides the experiment could be more easily performed.
From the fact that for 10 out of 14 dyes the saturation values agrees with each other, being 4.71×10-2 eq./kg., ± 2%, it is deduced that the sites (terminal amino groups in Amilan) would be stoichiometrically occupied not only by monobasic dyes, but also by polybasic dyes. Moreover, it was observed that the affinity increases with the molecular weight of dyes; i.e., when a benzene ring is substituted with a naphthalene ring, it increases by 2.1 Kcal. and 1.7 Kcal. for monobasic and dibasic dyes respectively. Also if an additional benzene-azo group is introduced into the molecules, the increment of affnities becomes 3.5 Kcal. and 3.0 Kcal. for respective cases.
