What are reactive dyes? What are the advantages and disadvantages of reactive dyeing?
2024-06-11 14:43:20 Source: Global Textile Network
Reactive dyes, also known as reactive dyes, are a new type of water-soluble dyes that appeared in the 1950s. Reactive dye molecules contain reactive groups that can react with hydroxyl groups in cellulose and amino groups in protein fibers. When dyeing, they form covalent bonds with fibers to generate "dye fiber" compounds.
Reactive dyes are characterized by bright color, good dyeing uniformity, simple method, high color fastness, complete color spectrum and low cost. They are mainly used for dyeing and printing of cotton, linen, viscose, silk, wool and other fibers and their blends.
Classification of reactive dyes:
According to the different reactive groups, reactive dyes can be divided into two main categories.
Symmetric triazobenzene type:
Among these reactive dyes, the chemical properties of the chlorine atom of the reactive group are more active. During dyeing, the chlorine atom is replaced by cellulose fiber in alkaline medium and leaves as a leaving group. The reaction between dyes and cellulose fibers belongs to bimolecular nucleophilic substitution reaction.
Vinyl sulfone type:
The active group contained in such reactive dyes is vinyl sulfone (D-SO2CH=CH2) or β - hydroxyethyl sulfone sulfate. During dyeing, β - hydroxyethyl sulfonyl sulfate is eliminated in alkaline medium to form vinylsulfonyl group, which is then combined with cellulose fiber to form covalent bond through nucleophilic addition reaction.
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 dye molecules in recent years, which are called bi reactive dyes.
Advantages and disadvantages of reactive dyes:
advantage
Reactive dyes, which are composed of parent dyes, linkers and reactive groups, can form strong covalent bonds with fibers when used, and have a series of characteristics that other cellulose fiber dyes cannot match
(1) Reactive dyes are one of the best choices to replace banned dyes and other types of cellulose dyes such as sulfur dyes, ice dyes and vat dyes.
(2) Reactive dyes can obtain high level of various fastness properties with economical dyeing process and simple dyeing operation.
(3) Reactive dyes have wide color spectrum, bright color, excellent performance and strong applicability, which are suitable for the requirements of the market for fibers and clothing materials.
(4) Reactive dyes are suitable for printing and dyeing of new cellulosic fiber products such as Lyocell fiber.
shortcoming
(1) The utilization rate is not high enough, generally 60%~70%, producing a large amount of colored sewage.
(2) In order to restrain the charge on the fiber surface, reactive dyes need to use a considerable amount of electrolyte, which not only increases the labor intensity, but also greatly increases the difficulty of treating reactive dye dyeing wastewater.
(3) Some color fastness can not meet the market requirements, such as sweat light fastness, wet rubbing fastness, and light color fastness of azo red dyes and azo blue dyes.
(4) There are few dark colors that can replace vulcanizates and vat dyes.
