Principle of reactive dye soap washing process

Reactive dyes is one of the cellulose fiber and its blended fabric dyeing main variety of dyes, reactive dyes structure contains active group, in alkaline conditions can react with hydroxyl groups on the cellulose fibre, through nucleophilic addition or nucleophilic substitution reaction to form covalent bonds and dyeing.

Solid color reaction of cellulose structure of hydroxy ionization as nucleophilic reagent, dyeing medium water ionization, hydroxyl ions to form another nucleophilic reagent, hydrolyzed dye and reactive dye reaction.

Hydrolyzed and unfixed dyes are the main factors affecting the fastness of dyeing and must be removed by soap washing.

After dyeing soaping aim is to remove not fixation of dyes on textiles, alkali hydrolyzed dye, electrolyte, etc., improve the color fastness of the dye products, vividness, shooting and other performance.

Soap washing mechanism (FIG. 1)


The soap washing mechanism is shown in figure 1. The soap detergent adsorbs on the fiber surface and penetrates into the fiber gaps. By reducing the surface tension, the binding force of unanchored dyes and hydrolyzed dyes on fibers is reduced, and the fibers are separated by mechanical action. The stable system is formed by the wetting, emulsifying, dispersing, solubilizing and complexing of the dye by the soap detergent to prevent the dye from contaminating the fiber.

There are three processes of washing and removing dyes in water washing:

1) the dye in the capillary network dyeing solution on the fiber surface or between fibers is diluted and exchanged by water when washing;

2) the dye in the fiber channel first diffuses from the fiber channel dye solution to the fiber surface and is desorbed and then removed by washing, dilution and exchange;

3) some insoluble dye aggregates on the fiber surface are mainly separated from the fiber by mechanical force and dispersed into the lotion. The emulsifying, chelating and dispersing effects of soap detergent on unanchored and hydrolyzed dyes have a direct impact on the washing effect.

Hydrolysis of the fibers has certain direct dye, it not only exists in the surface of fiber, more is inside the fiber channel, in addition to the fiber surface through the dilution of water exchange when catharsis, more is through the desorption, diffusion, from inside the fiber channel walls of desorption, diffusion to the fiber surface, and then through the dilution of water exchange, soap lotion chelate disperse removal.

The electrolyte has no direct property to the fiber and is removed mainly through the dilution and exchange of water washing liquid. Hot water washing can dissolve cellulosic fibers, and make the electrolyte in the pores diffuse rapidly to the surface of the fibers. The electrolyte can be effectively removed by dilution exchange.

Hydroxide anion in alkali agent has a certain directness to cellulose fiber, which diffuses relatively slowly in the pores. Once it reaches the fiber surface, it is neutralized with the acid in the water bath and removed. Large amount of flowing water can be removed quickly. The good permeability of acid will help to neutralize the remaining alkali on the fiber surface and in the pore.

The traditional soaping process is through acid neutralization residual alkali, after staining of 95 ℃ high temperature soaping remove not dye fixation and hydrolyzed dye, washed to remove electrolytes, washing water, washing time is long, large energy consumption. In order to improve the efficiency, to realize low temperature soaping, researchers have developed a surface active agent, chelating, chelate disperse and distribution and so on the many kinds of soap lotion, can effectively remove electrolytes, alkali and floating color.