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 the hydroxyl groups on the cellulose fibers. The amino groups on protein fibers and polyamide fibers undergo chemical reactions to form covalent bonds, so their dyeing 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 active groups in the reactive dye molecules are easy to hydrolyze. During storage and use, a certain amount of reactive dyes are lost due to hydrolysis of the active groups. Reactive, remaining in the dye liquor causing waste.
Dyeing mechanism of reactive dyes
During dyeing, the active groups form covalent bonds with the primary alcoholic hydroxyl compounds on the fiber, thus obtaining excellent wet processing fastness. When dyeing with reactive dyes, the fiber first reacts with the alkali in the dye bath to generate cellulose negative ions.
Then the negative ions of cellulose react with the reactive dye to generate a “dye-fiber” compound,
Experiments have shown that different pH values have different concentrations of cellulose negative ions.
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 nucleophilic substitution and philophilic substitution. There are two types of core additions.
Nucleophilic substitution reaction of reactive dyes
Dichlorobenzene type and dichlorobenzene type reactive dyes undergo nucleophilic substitution reaction with cellulose anions to generate esters.
The carbon atom on the nucleus connected to the chlorine atom in the reactive dye molecule has a high positive charge density, and is the nucleophilic reaction center for cellulose negative ions. The “dye fiber” compound can be regarded as an ester of trimeric acid, and the reaction is irreversible.
Nucleophilic addition reaction of reactive dyes
After the vinyl sulfone reactive dye interacts with cellulose negative ions, a nucleophilic addition reaction occurs to form an ether bond.
The conjugation effect of the reactive dye molecules due to the sulfone group 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, under the action of alkali, a hydrogen ion is first removed from the α carbon atom, and then the β carbon atom loses the negative ion of cellulose, and a vinyl sulfone group is generated, so the ether bond is generated. Nucleophilic addition reactions are reversible.
Application scope of reactive dyes
Reactive dyes can dye a variety of fibers. In addition to being used for dyeing and printing cellulose fibers such as cotton, linen, and viscose, they can also be used for wool, silk And dyeing of synthetic fibers such as nylon.
微信扫一扫打赏
