Reactive dyes, also known as reactive dyes, are a new type of water-soluble dyes that appeared in the 1950s. The molecules of reactive dyes contain reactive groups that can react with hydroxyl groups in cellulose and amino groups in protein fibers. A covalent bond is formed to generate a "dye-fiber" compound. Reactive dyes have the characteristics of bright colors, good level dyeing, simple dyeing method, high dye fastness, complete chromatogram and low cost. They are mainly used for dyeing cotton, linen, viscose, silk, wool and other fibers and their blended fabrics. And printing.
definition
Reactive dyes are also called reactive dyes. The molecule contains a chemically active group that can react with cotton, wool and other fibers in an aqueous solution to form a co-bonded dye. Has high washing fastness
classification
According to different reactive groups, reactive dyes can be divided into two main categories.
formula
Symmetric triazine type The general formula is:
In the formula, D is the parent dye. In this kind of reactive dyes, the chemical nature of the chlorine atom of the reactive group is more active. During dyeing, chlorine atoms are replaced by cellulose fibers in alkaline medium and become leaving groups and leave. The reaction between the dye and the cellulose fiber is a bimolecular nucleophilic substitution reaction (see substitution reaction).
Vinyl sulfone type "The reactive group contained in this type of reactive dyes is vinyl sulfone (D-SO2CH=CH2) or β-hydroxyethyl sulfone sulfate. During dyeing, β-hydroxyethyl sulfone sulfate ester undergoes elimination reaction to generate vinyl sulfone group in alkaline medium, then combines with cellulose fiber and undergoes nucleophilic addition reaction to form a covalent bond.
The above two types of reactive dyes are the main reactive dyes with the largest output in the world. In order to improve the fixation rate of reactive dyes, two reactive groups have been introduced into the dye molecule in recent years, called dual reactive dyes. In addition to the varieties for cellulose fibers, reactive dyes have also developed varieties for protein fibers (such as silk, wool and other fibers).