Disperse dyes are used every day, but can you tell me at once why glacial acetic acid is added to adjust the pH value when dyeing with disperse dyes? (Nowadays, organic acids are added to adjust the pH value, except for alkaline disperse dyeing)
The reason is:
The stability of disperse dyes in the dye bath is closely related to the pH value. Especially at high temperatures and high pressures, if the pH value of the dye bath is not strictly controlled, color variation will often occur. The main reasons are as follows.
(1) Causes accelerated hydrolysis of disperse dyes. In the manufacturing process of dyes, a large amount of dispersants such as diffusing agent NNO, lignin, sodium carbonate, etc. are often added to make the dye solution weakly alkaline.
When dyeing at 130% high temperature, it is easy to hydrolyze, resulting in light dyeing and dull color.
(2) Due to the reductive decomposition of disperse dyes, the chromophoric group is lost. This phenomenon is common in dyes with azo structure.
(3) The phenol group in the molecular structure of the dye causes an ionic reaction due to the action of alkali, and the water solubility is enhanced, while the dyeing is correspondingly weakened. Often due to the addition of a dispersant in the dye bath, the dye dispersion is weakly alkaline. .
Therefore, disperse dye dyeing is usually carried out in a weakly acidic dye bath, and the pH value is generally adjusted within the range of 5 to 6. In order to keep the dye bath weakly acidic, it is often adjusted with acetic acid.
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