The effects of tannic acid on the diffusion behaviors of 18 kinds of disperse, acid and basic dyes in nylon 6 films were studied by the film roll method using a dyebath of pH 4.2 and 6.1 at 70°C.
Both the content of surface dye adsorption,
Cs, and extrapolated value of diffusion coefficient to zero concentration of dye in the film,
Do, of disperse dyes decreased slightly with increasing in tannic acid content of the film, however,
Cs and
Do were scarcely affected by change in pH of dyebath. For acid dyes,
Cs and
Do decreased markedly as tannic acid content in the film and pH of dyebath increased.
The decreases in
Cs and
Do were observed remarkably when dyes involved two or mor sulfonic acid groups, which indicated that those dyes is expected to be fixed more effectively by tannic acid treatment.
These decreases may be attributed mainly to electrostatic repulsion between the dye anion and the dissociated phenolic hydroxyl groups of tannic acid. On the other hand,
Cs of basic dyes increased and
Do decreased by tannic acid treatment. These changes in
Cs and
Do are due to the electrostatic attraction between the dye cation and tannic acid.
From these results, it seemed that the electrostatic interaction between dye and tannic acid adsorbed in nylon plays an important role in the dye fixation.
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