Why do reactive dyes agglomerateⅠ

Reactive dyes have a very good dissolution state in water. Reactive dyes mainly rely on the sulfonic acid group on the dye molecule to dissolve in water. -Ethylsulfonyl sulfate is also a very good solubilizing group.

In the aqueous solution, the sodium ion on the sulfonic acid group and the -ethylsulfone sulfate group undergoes a hydration reaction to make the dye form anion and dissolve in water. The dyeing of reactive dyes depends on the negative ions of the dyes to dye the fibers. The solubility of reactive dyes is more than 100 g/L. The solubility of most dyes is 200-400 g/L, and some dyes can even reach 450 g/L. However, during the dyeing process, the solubility of the dye will decrease (or even completely insoluble) for various reasons.

When the solubility of the dye decreases, part of the dye will change from a single free anion to a particle, because the charge repulsion between the particles is greatly reduced.

Particles and particles will attract each other to produce agglomeration. This kind of agglomeration is that the dye particles first gather into agglomerates, then transform into agglomerates, and finally transform into flocs. Although the floc is a loose collection, due to the electric double layer formed by the positive and negative charges around it, it is difficult to decompose it by the shear force during the circulation of the dye liquor, and the floc is easily in the fabric. Precipitate on the surface, resulting in surface staining or smearing.

Once the dyes produce such agglomeration, the dyeing fastness will be significantly reduced, and at the same time, different degrees of color flowers, stains and stains will be caused. For some dyes, the aggregation of the flocs will further accelerate under the shear force of the dye liquor, resulting in dehydration and salting out. Once salting out occurs, the color of the dyeing will become extremely light, or even not dyed, even if dyed, it will be seriously colored and stained.

The main reason for the agglomeration of dyes is caused by electrolytes. In the dyeing process, the main electrolytes are dye accelerators (yuanming powder and salt). The dye accelerators contain sodium ions, while the sodium ion equivalent in the dye molecules is much lower. Due to the sodium ion equivalent number of the dye accelerator, the normal concentration of the dye accelerator in the normal dyeing process will not have much influence on the solubility of the dye in the dye bath.

However, when the amount of dye accelerator increases, the concentration of sodium ions in the solution also increases accordingly. Excessive sodium ions will inhibit the ionization of sodium ions on the dissolving groups of dye molecules, thereby reducing the solubility of dyes. When the concentration of dye accelerator exceeds 200 g/L, most dyes will agglomerate to varying degrees. When the concentration of the dye accelerator exceeds 250 g/L, the degree of aggregation will be intensified, forming agglomerates first, and then quickly forming agglomerates and flocs under the shear force of the dye solution. For some dyes with low solubility, the Part of the salt is precipitated out and even dehydrated.

The anti-coagulation and salting-out resistance of dyes with different molecular structures are also different. The lower the solubility, the worse the anti-coagulation and salting-out resistance. The solubility of dyes is mainly determined by the number of sulfonic acid groups and the number of β-ethylsulfone sulfates in the dye molecule.

At the same time, the larger the hydrophilicity of the dye molecule, the higher the solubility, and the smaller the hydrophilicity, the lower the solubility. (For example, azo-structured dyes are more hydrophilic than heterocyclic-structured dyes.) In addition, the larger the molecular structure of the dye, the lower the solubility, and the smaller the molecular structure, the higher the solubility.