Reactive dyes are a new type of dye. This type of dye molecules contains active groups that can react with fibers. During dyeing, they can form covalent bonds with fibers to form a “dye-fiber” whole.
Since the molecules of reactive dyes contain one or more reactive groups, under appropriate conditions, these reactive groups can interact with cellulose fibers. The hydroxyl groups, protein fibers and amino groups on the polyamide fibers react chemically to form covalent bonds, so the color fastness is very good. Most of the molecular structures of reactive dyes are relatively simple, so they are easy to manufacture. Since the reactive dye molecules contain water-soluble groups such as sulfonic acid groups, they have good water solubility and level dyeing properties. And because most of the parent materials of reactive dyes are acid dyes, their colors are very bright and their prices are relatively cheap. Although reactive dyes have not been around for a long time, they have become very important dyes in dyeing and printing.
Because the reactive groups in the reactive dye molecules are easily hydrolyzed. During storage and use, a certain amount of reactive dyes lose their activity due to the hydrolysis of their reactive groups and remain in the dye liquor causing waste.
Dyeing mechanism of reactive dyes
During dyeing, the reactive groups form covalent bonds with the primary alcohol hydroxyl compounds on the fiber, thus obtaining excellent wet treatment Fastness. When dyeing with reactive dyes, the fiber first reacts with the alkali in the dye bath to generate cellulose negative ions.
Then the cellulose negative ions react with the reactive dye to generate a “dye-fiber” compound.
Experiments have proven that the concentration of cellulose negative ions is different at different pH values.
In addition, different reactive groups have different bonding conditions with cellulose anions during the dyeing process. According to the reaction type, they can be divided into two types: nucleophilic substitution and nucleophilic addition.
Reactive dyeNucleophilic Substitution reaction
Dichlorobenzene type and dichlorobenzene type reactive dyes undergo nucleophilic substitution reaction with cellulose anions to form esters.
The carbon atom on the nucleus connected to the chlorine atom in the reactive dye molecule has a high positive charge density, which is the nucleophilic reaction center for cellulose anions. The generated “dye fiber” compound can be used as Treated as an ester of trimeric acid, the reaction is irreversible.
Nucleophilic addition reaction of reactive dyes
After the vinyl sulfone type reactive dye reacts with cellulose negative ions, a nucleophilic addition reaction occurs to generate an ether bond.
Reactive dye molecules are caused by the sulfone group The conjugation effect increases the positive charge density on the β carbon atom, causing an addition reaction with cellulose negative ions. When the “dye fiber” compound is generated, a hydrogen is first removed from the α carbon atom under the action of alkali. ion, then the β carbon atom loses the cellulose negative ion, and a vinyl sulfone group is generated, so the nucleophilic addition reaction to generate the ether bond is reversible.
Application scope of reactive dyes
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Reactive dyes can dye a variety of fibers. In addition to being used for dyeing and printing cellulosic fibers such as cotton, linen, and viscose, they can also be used for dyeing synthetic fibers such as wool, silk, and nylon. .
