Views: 12 Author: Site Editor Publish Time: 2022-02-18 Origin: Site
Cotton fiber belongs to natural cellulose fiber. Cotton fabric has soft hand feel, good moisture absorption and air permeability and excellent wearing performance. As people pay more and more attention to wearing health and advocating nature, cotton fabric is loved by people. Reactive dyes are one of the main dyes for dyeing cotton fabrics. The market is basically dominated by reactive dyes, and a small part of vat dyes and sulfur dyes have been eliminated due to environmental protection reasons. However, reactive dyes are easy to be hydrolyzed. In the traditional process, there are problems of low dye uptake and color fixation rate. The utilization rate of dyes is low, and a large amount of colored sewage is generated. Alkali agent needs to be added in the stage, and the dye is easily hydrolyzed under alkaline conditions, resulting in a decrease in the utilization rate of the dye. In order to remove hydrolyzed and unfixed dyes, a time-consuming, energy-intensive and expensive washing process is often required. The washing process not only brings a large amount of wastewater, but also increases the difficulty of subsequent wastewater treatment, and the cost of wastewater treatment is greatly increased. Based on this, the dyeing of reactive dyes and the fixation of cotton fabrics have become a hot topic of research in recent years.
Structure of reactive dyes
Reactive dyes are water-soluble dyes with active groups in the molecular structure, which can be covalently bonded to hydroxyl groups on cellulose fibers and amino groups on protein fibers.
The structure of reactive dyes can be represented by the following general formula W-D-B-R, where W is a water-soluble group, D is a chromophore, B is a reactive group and a chromophore linking group, and R is a reactive group. Dyeing involves the reaction of dyes with fibers to form covalent bonds. The dye structure determines the reactivity, fixation rate, color fastness and application conditions of reactive dyes.
Single reactive group reactive dyes can be divided into X-type, K-type and KN-type according to their reactivity: X-type reactive dyes have strong reactivity, low stability, easy to hydrolyze, but fast dyeing rate, suitable for low temperature dyeing; K-type dyes have weak reactivity and high stability, and are suitable for dyeing at higher temperatures; KN-type reactive dyes have performance and dyeing conditions between the two. The overflow machine and airflow machine dyeing on the market are mainly KN type.
Advantages and disadvantages of reactive dyes
1 The advantages of reactive dyes
① Covalent bond between reactive dyes and fibers, in general, this bond will not dissociate, so once reactive dyes are dyed on fibers, they have good color fastness, especially wet fastness .
②Brightness of color and brightness are particularly good;
③ The cost is lower than that of vat dyes;
④ Complete chromatogram.
2 Disadvantages of reactive dyes
①Poor chlorine resistance and light fastness;
②It is easy to be hydrolyzed in water, the utilization rate is low, and a large amount of colored sewage is produced. In order to meet the needs of the fixation of reactive dyes, an alkali agent needs to be added in the dyeing stage, and the dyes are easily hydrolyzed under alkaline conditions, resulting in a decrease in the utilization rate of the dyes.