Dyeing Dyeing operation is performed by the reaction between fiber and dyes. Some

dyes are water soluble and some are water insoluble. Some fiber has affinity to

dye some have no affinity to dyes. So dyeing depends on both fiber and dyes

chemical properties.

Reactive dyes are the most common and huge uses dyes all over the world. Most

of the dyeing operation of natural fiber is done by reactive dyes.

Reactive Dye

In a reactive dye a chromophore contains a substituent that reacts with the

substrate. Reactive dyes have good fastness properties owing to the bonding that

occurs during dyeing. Reactive dyes are most commonly used in dyeing of

cellulose like cotton or flax, but also wool is dyeable with reactive dyes. Reactive

dyeing is the most important method for the coloration of cellulosic fibres.

Reactive dyes can also be applied on wool and nylon in the latter case they are

applied under weakly acidic conditions. Reactive dyes have a low utilization

degree compared to other types of dyestuff, since the functional group also

bonds to water, creating hydrolysis.

Reactive dye is only class of dyes which makes covalent bond with the fiber and

becomes a part of it. This can be described as: Reactive dyes + Fiber = Reactive dye-Fiber If the general structure of a reactive dye is “R-B-X” then, R-B-X + Fiber = R-B-X-Fiber (Dyed fiber) where, R = Chromophore Group (Azo, Anthaquinone, Phthalocyanine, Metal complex group) B = Bridging Group ( Imino, Ethyl & Methyl, Oxide, Sulphide group) X = Reactive Group (-Cl, -Br, -SH, -OCH, etc)

Chemical structure of reactive dyes

Characteristics of reactive dyes

Below structures are the examples of reactive dyes

ß-Sulphato ethyl Sulphone Type Dye-SO2 –CH2-CH2-OSO3H The electron attracting sulphone group causes electron deficiency on the terminal carbon atom enabling nucleophilic attack to take place. . (Addition reaction) Dye-SO2-CH=CH2 + O-R1 H (+) Dye-SO2-CH2- CH2-OR1 Where [O-R1]- is [Cellulose O -] or [OH -] of water, etc.

Remazols are reactive dyes based on Vinyl Sulphone system

Classification of Reactive Dyes: 1) By depending on chemical constitution reactive dyes can be

classified as: Chlorotriazine Dyes (MCT)

Vinyl Sulphone Dyes (VS)

Heterocyclic Helogen Containing Dyes (HHC)

Mixed Dyes (MCT-VS)

2) By depending on application methods of temperature,

reactive dyes can be classified as:

I.Cold brand reactive dyes:

This type of reactive dyes is applied in very low temperature. Temperature

lies between 25 -50 degree Celsius. They are highly reactive with fiber on

this temperature.

II.Medium brand reactive dyes:

This type of dyes is applied in a medium temperature range is 40 – 60

degree Celsius. Their reactivity is medium with fiber.

III.Low brand reactive dyes:

This type of dyes has very low reactivity properties with fiber with

comparison with medium and high brand reactive dyes. Dyeing is carried

out on 60 -90 degree Celsius. React ive dye is only class of dyes which makes co- val ent bond wi th t he f iber and becomes a par t of it. This can be described as:

React ive dyes + Fiber = Reactive dye-Fiber (Co-valent bonding)

I f t he general structure of a r eactive dye is “R-B-X” then,

R- B- X + Fiber = R-B-X- Fiber (Dyed fiber)

Her e,

R = Chromophor e Group (Azo, Ant haquinone, Pht halocyanine, Metal compl ex group)

B = Bridging Group ( Imino, Ethyl & Methyl, Oxide, Sulphide group)

X = Reactive Group (-Cl , -Br, -SH, -OCH, etc)

Exam ples of reactive dyes: