Definition of Reactive dye:
Reactive dyes are anionic soluble dyes. Those dyes are applied through a chemical reaction, the mechanism of which is complicated. Reactive dyes react with the ` fiber to form a covalent bond. They possess in their dye molecule a reactive group of Reactive dyes that reacts with the hydroxyl groups of the cellulose (cotton, flex, jute) to form a stable chemical linkage. The dyestuff of Reactive dyes thus becomes a part of the fibre substance.
The development of reactive dyes:
The dyeing of cotton fiber with direct dyes has relatively poor textile washing fastness. Only weak polar and dispersion forces bind the dye molecules to the cellulose fiber's polymer chains. During washing, "Direct dye" molecules can quickly diffuse out of the cotton polymer chain. The best fastness to washing perfect textile materials requires precipitating an insoluble pigment and mechanically trapping it within the cotton fibers.
However, this type of dyeing process with vat and azoic dyes is much more complicated than direct dyeing.
The idea of immobilizing a dye molecule by covalent bond formation with reactive groups in a fibre originated in the early 1900s. Various chemicals were found that "reactive group" of reactive dyes reacted with the hydroxyl groups of cellulose and eventually converted into colored cellulose derivatives, especially cotton.
Several dyes now known to be capable of covalent bond formation with groups in wool and cotton were not initially considered fiber-reactive dyes, despite the excellent fastness of washing their dyeing.
In 1955, Ratte and Stephen, working for ICI in England, developed a procedure for dyeing the cotton with fiber-reactive dyes containing "dichlorotriazine" groups. They established that dyeing cotton with these dyes under mild alkaline conditions resulted in a reactive chlorine atom on the triazine ring being substituted by an oxygen atom from a cellulose hydroxyl group. The role of the alkali is to cause acidic dissociation of some of the hydroxyl groups in the cellulose, and it is the "cellulosate ion" (Cell-O ) that reacts with the dye.
Cell-OH + HO- Cell-O- + H20
Cell-O + Dye – CI Cell - O - Dye + Cl-
Where Cell-OH is the cellulose with a reactive hydroxyl group, Dye-Cl is the dye with its reactive chlorine atom, and Cell-O-Dye is the dye linked to the cellulose by a covalent bond.
Market situation of reactive dye:
In the US, cotton represents approximately one-third of the fiber used in textile processing. Reactive dyes are essential for dyeing and printing cotton and other cellulosic blends. They represent about 45% (by value) of colorants used for coloring cellulosic fibers. Reasons for the success of reactive dyes include,
flexible application methods,
wide range of shades available (including brilliant shades),
their fastness properties,
and Cost-efficiency.
The demands made on reactive dyes are wide-ranging. Requirements depend primarily on the specifications for particular textile articles and operating conditions (equipment available legal constraints). Economic considerations, quality requirements, and ecological issues are significant factors in the debate concerning the ideal reactive dyeing process and optimum dyestuff selection. Over 60% of reactive dyes are applied by the exhaust dyeing method. The remainder is used by the padding method of dyeing.
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Last update: May-2022
