Reactive dye agglomeration phenomenon

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　Reactive dyes have a very good solubility in water. Reactive dyes mainly rely on the sulfonic acid groups on the dye molecules to dissolve in water. For medium-temperature reactive dyes containing vinyl sulfone groups, in addition to the sulfonic acid groups, their β-ethyl sulfone sulfate groups are also very good soluble groups. In an aqueous solution, the sodium ions on the sulfonic acid group and the -ethylsulfonyl sulfate group undergo a hydration reaction, causing the dye to form negative ions and dissolve in water. 　　Reactive dye dyeing relies on the negative ions of the dye to be dyed onto the fiber. The solubility of reactive dyes exceeds 100 g/L. The solubility of most dyes is between 200 and 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 become completely insoluble) for various reasons. When the solubility of the dye decreases, some dyes will transform from single free negative ions into particles. Due to the charge repulsion between particles, * * reduce. Therefore, particles will attract each other to form agglomeration. This agglomeration first assembles the dye particles into agglomerates, then transforms into aggregates, and finally transforms into flocs. Although flocs are a loose collection, due to the double electric layer formed around them by positive and negative charges, it is difficult to decompose them due to the shear force during general dye liquor circulation. The flocs can easily precipitate on the fabric, causing surface staining or staining. Once the dyes produce such agglomeration, the dye fastness will be significantly reduced, and at the same time, varying degrees of color flowers, stains, and stains will be caused. For some dyes (dyes with a general heterocyclic structure), their flocculates will further accelerate their aggregation under the shear force of the dye liquor, causing dehydration and salting out. Once salting out occurs, the dyed color will become very light or even uncolored. Even if it is dyed, it will cause serious stains and stains. There are many reasons for dye aggregation, but the main reason is caused by electrolytes. In the dyeing process, the main electrolytes are dye accelerators (yuanming powder and salt). The dye accelerators contain sodium ions, and the sodium ion equivalents in the dye molecules are much lower than the sodium ion equivalents of the dye accelerator. In the normal dyeing process, the normal dye accelerator concentration will not have much impact on the solubility of the dye in the dye bath. However, when the amount of dye promoter increases, the concentration of sodium ions in the solution also increases accordingly. Excess sodium ions will inhibit the ionization of sodium ions on the dissolving groups of the dye molecules, thereby reducing the solubility of the dye. When the dye accelerator concentration exceeds 200 g/L, most dyes will agglomerate to varying degrees. When the dye accelerator concentration exceeds 250 g/L, the degree of aggregation will intensify. Aggregates will be formed first, and then aggregates and flocs will quickly form under the shear force of the dye liquor. Some dyes with low solubility will partially salt out or even dehydrate.