EFFECTS OF pH AND IONIC STRENGTH ON THE DIFFUSION OF ANTHRAQUINONE ACID DYES IN NYLON 6 FILMS TREATED WITH TANNIC ACID

Abstract

The diffusion behaviors of anthraquinone acid dyes, C. I. 61570 and C. I. 62000, in nylon 6 films containing various amounts of tannic acid have been studied. The diffusion measurements were carried out by the film roll method in dye baths of varying pH's and ionic strengths at 70°C.
The pH dependences of diffusion profile, surface adsorption, C_s, and diffusion coefficient, D, of these dyes were almost similar to those of monoazo acid dyes reported in our preceding papers. Further, the extrapolated value of D at C (dye concentration in the nylon film)=0, D₀, which is regarded as a measure of the dye mobility independent of dye concentration in nylon, decreased with increased tannic acid content of nylon. These results support the speculation presented in a previous report, that the sorption and diffusion of acid dyes in nylon are suppressed by electrostatic repulsions between the dye anion and the negative charges of dissociated phenolic hydroxyl groups of tannic acid.
The effects of ionic strength, I_s, on the sorption and diffusion of C. I. 61570 at pH 4 were studied for nylon samples untreated and treated with tannic acid. In the latter case, noticeable I_s dependences were observed. Namely, the maximum diffusion coefficient, the corresponding dye concentration and C_s in tannic acid treated nylon, were suppressed at low Is. The increase in I_s brought these values up to those found for untreated nylon. D₀ values were lowered by the presence of tannic acid and the positive dependence of D₀ on I_s was stronger for treated nylon than for untreated one. These facts clearly evidence the existence of electrostatic interactions between the dye anion and the dissociated phenolic hydroxyl groups of tannic acid.