What is the effect of reactive dyeing salts on the dyeing process?

There are many varieties of reactive dyes, complete chromatography, simple process and relatively low price, so they are widely used. If color difference, color flower or cylinder difference occurs after dyeing, it is usually necessary to re-dye or repair the fabric. This not only affects the production efficiency, but also causes the waste of dyes, steam and water and the increase of sewage discharge, which in turn increases the production cost. In the current context of emphasizing environmental protection, the one-time success rate of dyeing is even more important. Generally speaking, reactive dyes have good water solubility, and the reactivity of different types of reactive dyes with cellulose is obviously different, and the fixation rate is relatively low. This is well understood by all manufacturers, such as using the same type of dyes for color matching, using corresponding temperature conditions for different types of dyes, etc., the application is relatively mature. However, many factories still have problems such as color difference, color flower, cylinder difference from time to time. This is mainly because the application properties of reactive dyes are not fully grasped. In fact, the dissolution and hydrolysis of reactive dyes are greatly affected by water quality, electrolytes, and alkaline agents, and different reactive dyes are affected to different degrees. Insufficient understanding of these problems may result in improper processing and operation, thus affecting the levelness and reproducibility of reactive dyeing.

When dyeing with reactive dyes, Yuanming powder or table salt is always used. Because of the low dye uptake of reactive dyes, the use of electrolytes can significantly improve this. However, salts can also significantly affect the dissolved state of reactive dyes, and even form aggregated particles in the dye solution, which can easily cause color stains, color flowers, or unstable dyeing quality.

Under the action of the salt electrolyte, the dielectric layer of the reactive dye anions in the solution becomes thinner, the repulsion between them is weakened, and they approach each other, and the aggregation of dye ions may be formed due to the attractive force between the hydrophobic structures.

The aggregation state of this dye ion actually exists in the absence of electrolyte, but the degree of aggregation is low. As the dyeing process progresses, these small aggregates will dissociate into individual dye ions. In other words, the dyeing is still carried out in a single-molecule state. When there are too many electrolytes, the highly aggregated dye ions are difficult to dissociate and stain the fibers, and then react with cellulose to fix the color to form color spots.

Of course, reactive dyes with different structures are affected to varying degrees. A dye with a large structure and few water-soluble groups is more likely to cause the aggregation of dye ions. The effect of electrolyte on the solubility of reactive dyes is indeed significant. This is likely to cause color stains or uneven dyeing during dyeing. Of course, it is well known that the increased rate of dye uptake caused by salt-promoted dyeing may also cause color blooms.