Reactive dyes

The term “reactive” dye means that the dye chemically reacts with the fiber. These dyes are chemically bonded to the fibers unlike other classes of dyes (direct, sulphur, vat) where dye is physically trapped in the fiber pores. This chemical bonding being very strong, the dye cannot be easily washed off. Hence reactive dyed fabrics possess excellent wash fastness properties.

•      In general these dyes are represented by

D-B-R-S

                             where D is colour bearing substance known as    chromogen, R is reactive group and B is the bridging     group which connects chromogen and reactive    group. The water soluble group, S, makes the dye        easily water soluble.

Depending up on nature of the reactive group these dyes are classified into three categories. They are triazinyl dyes, vinyl sulphone dyes and bi functional dyes.

i) Triazinyl Class

The triazinyl class of dyes also popularly known as Procion dyes    (A brand name of ICI) are further classified into two groups:

Monochloro triazinyl (MCT) dyes and Dichloro triazinyl dyes (DCT) dyes.

Cynauric Chloride (1,3,5 Triazine)

Dichlorotriazine

In this class of dyes the reactive group is chlorine. In alkaline medium, this chlorine atom reacts with hydroxyl group present in cellulose (cotton) thereby linking the dye with the fiber through a chemical bond (covalent bond). 

The reactivity of DCT dyes is high; hence they can dye (react with) cotton in the presence of an alkali at room temperature. They are commonly known as “cold brand” or “M brand” dyes.

On the other hand the reactivity of MCT dyes is low. They require high temperature (80^oC) and high alkaline condition to dye cotton. They are commonly known as “Hot brand” or “H brand” dyes.

The structures of MTC and DCT dyes and formation of covalent bond with hydroxyl groups present in cotton (Cell-OH).

                        

ii)Vinyl Sulphone class

The second category of reactive dyes are known as vinyl sulphone dyes (VS).  These dyes are popularly known as Remazol dyes a brand name of Hoechst.  They have general structure as shown below. These dyes are applied on cotton in the presence of alkali at 60^oC.

iii) Bi functional dyes

The third category of reactive dyes is known as bi functional (BF) dyes. They have higher exhaustion when compared to the other classes of dyes. They are marketed as “HE” or “H-EXL” dyes. These dyes can be further divided into homo bi functional and hetero bi functional dyes.

The homo BF dyes can be either two triazinyl groups each having one reactive chlorine group or two VS groups; where as hetero BF dyes have one VS and one MCT group.

They are marketed as “ME” and “Sumifix Supra  Brand” dyes (Amino chlorotriazine sulphatoethylsulphone system).  These dyes are also applied on cotton in the presence of alkali at 60^oC. They have very good light fastness with rating about 6. Dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.

Dyeing with reactive dyes:

Textile materials dyed with reactive dyes have very good wash fastness, brighter shades and have moderate rubbing fastness.

Cellulose can be dyed using reactive dyes in following methods:

1. Batch wise dyeing
2. Continuous
3. Semi continuous