This document provides information about reactive dyes used for dyeing cotton fabrics. It discusses the general structure and properties of reactive dyes, including that they form covalent bonds with fibers. The document also summarizes the dyeing process, which involves dye exhaustion, fixation in an alkaline environment, and washing off unfixed dye. Factors that affect dye hydrolysis are outlined, such as liquor ratio, salt concentration, and temperature. The role of salt and alkali in the dyeing process is also explained.

1. Textile Engineering
Presented by:
Mazharul Islam
B.Sc. in Textile Engineering ( PTEC-10th Batch )
Dept. of Wet Process Engineering (WPE).
Email: tex.mazharul@gmail.com

2. 2
Dichlorotriazinyl Reactive Dye

3. Reactive Dye
Reactive dye:
In 1956 Rattee + Stephen (ICI) introduced “first” reactive dyes– chlorotriazines.
Reactive dye can be applied to cotton , silk and polyamide fibres successfully. But we apply the
reactive dye cotton substrate mainly. Reactive dye contains reactive group and this reactive
group makes covalent bond with the fibres and becomes part of the fibre.
The general structure of reactive dye is: D-B-G-X.
Why reactive dye is so called?
Reasons for so named: Reactive dye are so called because this is the only type of dye,
which has reactive group, and that’s reactive group reacts chemically with
fibre polymer molecules and form covalent bond. For this reasons the dye are so
called. The are also called ‘Fibre reactive group’.
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4. General formula of reactive dye :
Here,
D= Dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse dye etc.
B = Bridging part.
Bridging part may be –NH- group or –NR- group.
G = Reactive group bearing part.
X= reactive group.
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Fig. Dichlorotriazinyl reactive dye
Here, Azo Chromophore (−N=N−) Separated from Reactive Group to
Ensure the Colour Is Unaffected by Reaction with Fibre.
Sodium Sulphonate (NaSO3) is auxochromo act as water solubilizing group.

5. Properties of Reactive Dyes:
• Dyestuff react and combine chemically (covalently) with cellulose, so called
reactive dyes
• Water soluble dyes.
• Reactive dyes are Anionic in nature.
• Makes Covalent bonds with the fibres.
• Alkaline condition is must required for dyeing. (PH =11).
• Easy penetration and good leveling property.
• The have better Substantivity.
…………………………….
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6. Properties of Reactive Dyes: (cont….)
• Less substantive than direct dyes, hence more salt is required for exhaustion.
• Huge electrolyte is necessary for dyeing with reactive dyes.
• Fastness (wash, light, Rubbing, perspiration) properties are generally good
• Huge electrolyte is necessary for dyeing with reactive dyes.
• Comparatively cheap.
• All kinds of shade is found.
• Dyeing method is easy.
• Wide range of colors can be obtained and widely used in Bangladesh
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7. 7
Worldwide dye consumption:
 Reactive dye is water soluble.
 A certain amount of dye (10-40%) may react with water i.e. hydrolysis is occurred during dyeing
operation.
Popularity of Reactive Dye:
Reactive are mostly used for dyeing cellulosic fibres. At past cellulosic fibres were dyed with
direct and vat dyes, but after the introduction of reactive dyes there utility has become limited.
Reactive dyes are superior to direct dye in the following aspects:
i) Ability to procedure bright shades of wide range.
ii) High leveling quality.
iii) Good washing fastness.
iv) Good light fastness.
Dye Consumption%
Reactive 25
Disperse 20
Direct 10
Vat 10
Others 30

8. Definition of some important terms:
Dyeing:
The process by which a textile material is changed physically or chemically so that it looks
colorful is called Dyeing.
Coloring materials are mainly of three types. Dyes, pigments and lakes (ingrain dyes). A dye has
three parts in its structure chromophore, chromogen and auxochrome and is soluble in a
specific medium under certain conditions.
Dyestuff:
Dyes are colored, unsaturated organic chemical compounds capable of giving color to substrate
(textile) i.e. coloring or dyeing it. Dyes can be formed synthetically from relatively cheap basic
products where specific functional groups in the dyes which determine or affect the
applicability and fastness.
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9. Definition of some important terms: (cont..)
Chromophores:
The name is derived from the Greek chroma=color and phore from protein=to bear. The
group that causes the appearance of color when introduced into a chromogen and causes one
or more absorption brands to appear in the visible spectrum to mixture is acted on by UV rays
• Chromophores are unsaturated organic radicals.
• Their specific state of unsaturation enables them to absorb and reflect incident
electromagnetic radiation with in the very narrow band of visible light.
• The chromophores give the dye molecules its particular color.
• A molecules processing no chromophores would be colorless.
• Example of dyes: Direct dye, Acid dye, Vat, Basic, Disperse, Sulpher, Reactive dye etc.
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10. Auxochromes:
The name is derived from the Greek auxein = to increase and chroma = color. Auxochromes are
organic radicals.
The group present in dye except chromophore group is called Auxo- chromes.
They fulfil the following functions:
• Their presence influences the orbits of the loosely held electrons of the unsaturated bonds of
the chromophores. This also intensifies and deepens the hue of the dye molecules color.
• Auxochromes increase the overall polarity of the dye molecules and makes it more readily
soluble in water.
• The polarity of auxochromes enables the formation of the forces of the attraction between
the dye molecule and the fibre polymer. This improves the color fastness properties of dyed or
printed fibre.
• Example: Amino group (-NH2), Methyl amino (-NH-CH3), Hydroxyl group (-OH),
Carboxylic group (-COOH), Nitrate group (-NO3).
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11. Difference between Dyes & Pigments :
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Dye Pigments
1. Water solubility 70% 1. 100% water insoluble
2. Most of dyes are organic compounds. 2. Most of pigments are inorganic compound.
3. No binding agent is reqd 3. Required
4. Dye diffusions in the fabric 4. – On the fabric.
5. Costly 5. Cheap
6. Auxochorme present 6. Auxochrome not present.
Chromogen:
The dye structures which contain both chromophore and auxochrome is called chromogen.

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Dyeing mechanism of reactive dye:
The dyeing mechanism of cotton fabric with reactive dye takes place in 3 stages:
1)Exhaustion of dye in presence of electrolyte i.e. dyes adsorption.
2)Fixation (under the influence of alkali.)
3)Wash-off (remove the unfixed dye from material surface.)
Dye exhaustion:
When fiber is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye.
Here NaCl is used as the electrolyte. This electrolyte increases the adsorption of dyes. So
when the textile material is immersed into the dye liquor, the dye is exhausted on to the fiber.

13. Fixation:
Fixation of dye means the reaction of reactive group of dye with terminal –OH
or-NH2- group of fiber and thus forming strong covalent bond with the fiber.
This is an important phase, which is controlled by maintaining proper pH by
adding alkali. The alkali used for this creates proper pH in dye bath and work as
the dye-fixing agent (7). The reaction takes place in this stage is shown below:
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or

14. Wash-off:
As the dyeing is completed, a good wash must be applied to the material to
remove extra and unfixed dyes from material surface. This is necessary for level
dyeing and good fastness properties. It is done by a series of hot wash, cold wash
and soap solution wash.
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15. Classification of Reactive Dye
a) Classification on the basis of reactivity:
On the basis of reactivity reactive dyes are of three types. These are :
1) Low reactive dye
Reactivity of these dyes is low. So, highly alkaline environment is required for the fixation of these dyes with
substrate. Here PH is maintained 12-12.5 by using NaOH in bath. Example : Cibacron T , Drimarene.
2) Medium reactive dyes :
These are medium reactive dyes. Here pH is maintained 11-12 by using Na2CO3 (Soda ash) in dye bath. Example :
Levafix E, Remazol.
3) Higher reactive dye :
These dyes are highly reactive. So, fixation of these dyes is easy and lower alkaline medium is kept. Here pH is
maintained 10-11 by using NaHCO3 in dye bath.Exmaple: Procion Mx, Drimarene KLR.
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16. b) On the basis of Temperature and Method
i) Cold Brand Dyes:
These types of dyes are highly reactive as they posses highly reactive group in their constituent.
So dyeing of these dyes can be done in lower temperature i.e. 32-600C .Example : Procion Mx,
Levafix E, etc.
ii) Medium Brand:
These types of dye contain reactive group of moderate reactivity. So dyeing is done in higher
temperature than that of cold brand. Here temperature is kept between 600C to 710C.
iii) Hot Brand:
These types of dyes contain reactive groups of least reactivity. So high temperature is required
for dyeing i.e. 72-900C temperature is kept for dyeing. Example : Procion H, Cibacron T, etc.
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17. Modern classification of reactive dyes :
Reactive dyes have recently been classified as
1. Alkali-controllable reactive dyes :
These dye have relatively high reactivity and only moderate substantivity.
The reactive dyes are applied at relatively low temperatures and level dyeing requires careful control of the
addition of the alkali to initiate the fixation stage.
Examples include DCT, DFCP and VS reactive dyes.
2. Salt-controllable dyes.
These are dyes of relatively low reactivity towards cotton under alkaline conditions and therefore the dyeing
temperature will be as high as 80°C.
They have appreciable substantivity and level dyeing requires careful addition of salt to promote exhaustion.
Examples in this class include TCP, MCT as well as MFT reactive dyes.
3. Temperature-controllable dyes: which undergo fixation at high temperatures even under neutral
conditions. The NT dyes are in this class.
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18. Why Salt is used in Reactive dyeing Process:
(used as electrolyte)
Normally, Glauber's salt or common salt/Vacuum salt (NaCl) is used for this
purpose. Hence, Glauber's salt is always preferred over common salt. Glauber's salt
is a common name for sodium sulfate decahydrate, Na2SO4.10H2O.
The salt is used in reactive dyeing because of the following things-
1)Salt are used to increase the affinity of dye to fibre.
2)It decreases the hydrolysis rate of dyes.
3)It neutralize the electro negativity of fibre surface when immersed in solution.
4)It puts extra energy to push dye the fibre polymer i.e increase absorption.
5)The amount of salt used depend upon the shade to be produced-
6)For light shade 10-20 gm/litre salt is used.
7)For medium shade 30-50 gm./litre is used.
8)For deep shade 60-100 gm./litre is used.
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19. Why Alkali is used ? :
Alkali is used for the following purpose-
1) Alkali is used to maintain proper pH in dye bath & thus to create alkaline condition.
2) Alkali is used as a dye fixing agent.
3) With out alkali no dyeing will take place.
4) The strength of alkali used depend on the reactivity of dyes.
5) As strong alkali caustic (NaOH) is used to create pH 12-12.5 when the dye is of lower reactivity.
6) As medium alkali sods ash(Na2co3) is used to create pH 11-12. when the dye is of medium
reactivi
7) As weak alkali (NaHCO3) is used to create pH 10-11. when the dye is of high reactivity.
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20. Role of Salt in Reactive Dyeing:
Inorganic salts have two main functions in exhaustion dyeing with reactive dyestuffs:
Improving the affinity of the dyestuff
Acceleration of the dyestuff's association and lowering of its solubility.
Generally reactive dyes contains sulphonic acid (-SO3H) group which is insoluble in water.
During the manufacturing of the reactive dyes these sulphonic acid groups are converted
into
The sodium salt of sulphonic acid (-SO3Na) which is soluble in water.
Reactive dye – SO3H + Na⁺ → Reactive dye-SO3Na
Generally when the reactive dye goes in the water, it is solublised giving dye anions and
sodium cations
Reactive dye – SO3Na + Water -- → Reactive dye – SO3⁻ + Na⁺
(Dye anion) (Sodium cation) 2

21. Why Urea is used?:
Urea is used in continuous method of dyeing .It helps to get required shade of dye. To get
dark shade more urea is used and for light shade less amount of urea used.
Why Soaping is Required after reactive dyeing?:
By soaping the extra colour is removed from fibre surface (from fabric
surface) thus Wash fastness is improved. Soaping increases the brightness
and Stability of dye.
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22. Hydrolysis
Hydrolysis is a chemical process in which a molecule is converted into two parts by the
addition of molecule of water. One fragment of parent molecule gains a hydrogen ion (H+)
from the additional water molecule. The other group collects the remaining hydroxyl group
(OH-).
Hydrolysis of Reactive Dye/Technical defficiency of R.D:
Under alkaline condition, Reactive dyes react with the terminal hydroxyl group of cellulose.
But if the solution of the dye is kept for long time, its concentration drops. Then the dye
reacts with the hydroxyl group of water. The reaction of dye with water is called Hydrolysis
of reactive dye.
2
(b)

23. After hydrolysis dye cannot react with fibre. So hydrolysis increases the loss of dyes.
This hydrolysis occurs in two stages. At first the concentration of dye initially increases and
then begins to decrease. Where as the concentration of hydroxyl compound increases
continuously. Then the hydroxyl compound cannot react with dye.
I) Incase of Triazinyl dyes:
(a)
II ) In case of Vinyl Sulphone Dyes:
a) Dye-SO2CH = CH2 + HO – cellulose  Dye – SO2 CH2 -CH2 O – cellulose
b) Dye-SO2CH = CH2 + H-OH  Dye-SO2 CH2 CH2 OH
Mono hydroxy group
2
N
C
N C
N
C
HN
Cl
Cl
Dye
N
C
N C
N
C
HN
O
O
Dye+ Cell-OH
Cell
Cell
Dichloro triazinyl
N
C
N C
N
C
HN
Cl
Cl
Dye
N
C
N C
N
C
HN
OH
OH
Dye+ H-OH
Dihydroxy group
(b)

24. For preventing hydrolysis the following precautions are taken—
1. As hydrolysis increases with increasing temperature during dissolving and application
temperature should not be more than 40°C.
2. Dye and alkali solution are prepared separately and mixed just before using.
3. Dye and alkali should not be kept for long time after mixing.
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25. Factors affecting Dye Hydrolysis:
1) Liquor Ratio: Longer liquor ratio increases hydrolysis and vice versa.
2) Salt Concentration: Higher salt concentration increases hydrolysis and vice versa.
3) PH : Higher PH increases hydrolysis and vice versa.
4) Temperature : Higher temperature increases hydrolysis and vice versa,
5) Dye reactivity: Increase both hydrolysis and fixation rate.
6) Time : Higher dyeing time increases hydrolysis and vice versa.
7) Type and number of reactive group : Vinyl Sulphone is more prone to hydrolysis than
Triazinyl group.
8) Types of bridging group: The oxide (O-) and sulphide bridges are less stable in alkaline
hydrolysis. But more stable bridges decreases reaction rate along with the hydrolysis.
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26. Potential problems due to dye hydrolysis :
1) Hydrolysis accompanies fixation, resulting in incomplete utilization of dye. Hence dye
wastage occurs. Up to 40-60% dyes (avg. 50%) are wasted in this case.
2) Relatively large amount of electrolyte are required for exhaust, otherwise dye hydrolysis
will occur greatly dye bath.
3) Laborious removal of unreacted and hydrolyzed dye is required – often a longer operation
than the dyeing step itself and not always entirely satisfactory.
4) Longer washing operation for removal of unreacted and hydrolyzed dye often costs 50%
of total dyeing cost.
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27. 5) Hydrolyzed dye is discharged as colored effluent and effluent cost risen up. Moreover,
color is not easily removed by effluent treatment processes and in many cases the dyes are not
readily biodegradable.
6) Unhydrolyzed , unfixed heterocyclic reactive dyes may pose in environment hazard.
7) Despite reactive dyes being covalently bond with the substrate, fastness problems
associated can occur due to hydrolysis.
8) Less storage stability.
9) Trailing problems for continuous dyeing.
10) Running shade in batch process.
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28. <Md Mazharul Islam> WPE dept. 10th Batch, PTEC.
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Cotton fabric dyed with Reactive Dyes with Recipe and
Recipe Calculation (Next slide)
Drain
Fixingagent+
Softener
(45°C+20min)
Coldwash
(2-3times)
Temp(°C)
XO
Y
70
65
60
55
50
45
40
35
Dyes
Levelingagent
Salt
Wettingagent
SodaAsh
7 min5 min 60 min
Coldwashwith
AceticAcid
20
min
25 min
HotWashwith(or
not)SoapingAgent
60°C
85-95°C
Time (min)
Youtube

29. Thank You !
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