The document summarizes the general structure and properties of reactive dyes. Reactive dyes have a D-B-G-X structure, where D is the dye/chromogen, B is the bridging group, G is the reactive group, and X is the actual reactive functional group. Reactive dyes form covalent bonds with cellulosic fibers and have good wash and light fastness as a result. They are classified based on the number of reactive groups and dyeing temperature. Factors like pH, temperature, electrolyte concentration influence the dyeing process. Defects can occur but are remedied by washing or chemical treatment.

2. General Structure of Reactive Dyes
The general structure of reactive dye is: D-B-G-X.
Here,
D= dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse, premetallised dye etc.
B = bridging part.
Bridging part may be –NH- group or –NR- group.
G = reactive group bearing part.
X= reactive group.

3. Chemical structure of reactive
dyes:

4. Reactive Dyes:
 A dye which is capable of reacting chemically with a
substrate to form a covalent dye substrate linkage
 Only a class of dye that have a reactive Group in their
structure
 Covalent bond formation with the substrate

5. Characteristics of Reactive Dye:
Reactive group: Responsible for the reaction between the
substrate & dye molecule
Chromophoric group: Coloring agent
Bridging group: That links the reactive system to the
chromophore. Also influence the reactivity & degree of fixation.
Solubilizing group: Solubilizing agent

6. Classification of reactive
dyes:
Depending on chemical constitution reactive dyes can be
classified as:
Monofunctional Reactive system: Have only one reactive
system
Bifunctional Reactive system: Have two reactive system.
Homobifunctional reactive system and Heterobifunctional
reactive system
Polyfunctional reactive system: May have more then two
reactive system.

7. Depending on application method of temperature
reactive dyes can be classified as:
Cold Reactive dyes:
Dyes which have high reactivity need low temperature for
dyeing (25-50 0C)
Hot reactive dyes:
Dye which have low reactivity need high temperature for dyeing
the textile substrate (60-90 0C)

8. General properties of reactive
dyes:
 Reactive dye is anionic in nature.
 Reactive dye is a water soluble dye.
 They have better wash and light fastness properties.
 They have better substantivity.
 They form strong covalent bond with the cellulosic fibers.
 Alkaline condition is must required for dyeing.
 Electrolyte is must required for dye exhaustion in the fiber.
 Wide range of color can produce.
 Comparatively cheap in price.

9. Influencing factors
ph
Reactive dyeing is done in alkaline condition for this
reason ph of the dye bath should control. ph should be
between 11.5-11.
Temperature
Temperature should fix depending on the nature of dye.

10. Concentration of electrolyte
Concentration of electrolyte depends upon the type of
shade.
Substantivity:
Substantivity more depends upon chromophore as compared to
reactive system. A high substantivity may results:
Lower dye solubility.
High primary exhaustion.
A high reaction rate.

11. Defects in Dyeing with Reactive Dyes:
Defects:
Colors are not fast to washing, Abrasion, Staining in the fabric when
transporting from place to the other, water marks on the fabric.
Remedy:
Wash the fabric with soap and soda ash at right temperature.
Adding sequestering agent will yield good results. Treating with
Ammonia will also give good results.

12. Defect: The fabric has been dyed in darker shade,
uneven dyeing
Remedy:
To take out color from the fabric treat it with caustic for 45-60 min at
70 oC. Thereafter treat the fabric with 10-20 g/l . Acetic Acid for 40-60
min at 80-85 oC.
Defect:
Bleeding in colors during washing, abrasion.
Remedy:
Boil the fabric with caustic, Treat the fabric with Hydrogen
Peroxide ( 5-10 g/l, 60-70 oC) to make the color fast.

13. General steps of dyeing with
reactive dyes:
 Exhaustion of dyes
 Adsorption
 Diffusion of dye
 Migration of dye molecule
 Fixation of dye in the textile substrate

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