Reactive dye details

1. Presentation on: Dyeing of Cotton with Reactive Dye
Prepared By:
Tanvir Ahammed Rana
Id. 2012000400038
19th Batch, Textile Department.
SouthEast University.

2. Introduction
Reactive dyes are probably the most popular class of dyes to
produce 'fast dyeing' on piece goods. These were first
introduced a little over 40 years based on a principle which
has not been used before. These dyes react with fibre
forming a direct chemical linkage which is not easily
broken. Their low cost, ease of application, bright shades
produced by them coupled with good wash fastness make
them very popular with piece good dyers. Even in threads
these classes are gaining in popularity for cotton sewing.

3. Theory
A dye which is capable of reacting chemically with a substrate to from a covalent
dye-substrate linkage is known as a reactive dye.
Here the dye contains a reactive group and this reactive group makes covalent bond
with the fibre polymer and act as an integral part of fibre .This covalent bond is
formed between the dye molecules and the terminal –OH (hydroxyl) group cellulosic
fibres or between the dye molecules and the terminal amino (-NH 2) group of
polyamide fibres.
The general formula of reactive dye can be written as following:
D-X-Y
Here,
 D=Dye part( colour producing part).
 X=Bridge.
 Y=Functional group.
D-X-Y+ Fibre = Fibre covalent bond.

4. History of dyestuff
The historical development of the synthetic dyestuffs dates
back to 1856, when eighteen year old, W.H. Perkin
discovered the synthesis of Mauveine, a basic dye, by
accident, while he was engaged in the study of the action of
potassium dichromate on aniline Sulphate. He successfully
converted the process he had developed in laboratory to a
large-scale production, and demonstrated the application of
the dye on silk. The intermediates nitrobenzene and aniline
required in the production were also made commercially by
him. Nitrobenzene was earlier prepared by Mansfield in
1847.

5. Definition of dye
A dye is a coloured organic compound that absorbs
light strongly in the visible region and can firmly
attach to the fiber by virtue of chemical and
physical bonding between group of the dye and
group on the fiber. To be of commercial importance
a dye should be fast to light, rubbing and water.
Colour and dye have always played an important
role in the life of man from time immemorial.

6. Cellulosic fibers
The earliest cellulosic fibres were lines and cotton, both
of which have been used since remote antiquity. Linen,
or flax, is derived from ‘bast’ fibres of plants of the
Linum family, especially Linum usitatissimum. After
removal of glutinous and pectinous matter the fibre has
cellulose content of 82 – 83%. Cotton, which is fine hair
attached to seeds of various species of plants of the
Gossypium genus, has a cellulose content which may
reach 96%. Cellulose is a polymer of high molecular
weight consisting of long chains of D-glucose units
connected by B-1, 4- glucosidic bonds, and its structure
may be represented as follows:

7. Each glucose unit contains three alcoholic hydroxyl
groups, of which two are secondary and one is primary.
The degree of polymerization of cellulose varies from a
few hundred to 3500 or more.

8. Cotton
Cotton was considered a luxury fabric, as it was
imported all the way from India and usually dyed or
painted before it was shipped. Cotton was also valued
because of the brightness and colorfastness of the dyes
used to color it, and also for its use in making
candlewicks. Samples of cotton fabrics have been found
in India and Pakistan dating to 3000 BCE, but it did not
appear in Europe until the 4th century. Cotton waving
establishments were formed in Italy in the 13th & 14th
centuries but they did not make a significant economic
impact on the industry as they produced a coarser
quality of fabric than the imported fabric, and therefore
had difficulty in obtaining a good supply of cotton fiber.

9. Properties of reactive dye
1. Reactive dyes are anionic dyes which are used for dyeing cellulosic protein
polyamide fibres.
2. Reactive dyes are found in powder, liquid and print paste from.
3. During dyeing, the reactive group of this dye forms covalent bond with fibre
polymer and becomes an integral part of fibre.
4. Reactive dyes are soluble in water.
5. They have very good light fastness with rating about 6.
6. The dyes have very stable electron arrangement and the degrading effect
ultraviolet ray.
7. Reactive dyes give brighter shads and have moderate rubbing fastness.
8. Reactive dyes are comparatively cheap.
9. Reactive dyes have good perspiration fastness with rating 4-5.
10. Fixation occurs in alkaline condition

10. Assistants used for dyeing with reactive dyes
Salt:
As a salt, NaCI is used widely. The salt end 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 neutralizes the electro negativity of fibre surface when
immersed in solution.
4. It puts extra energy to push dye the fibre polymer ie
increase absorption.
 The amount of salt used depend upon the shade to be
produced-
 For light shade -10-20 gm/litre salt is used.
 For medium shade-30-50 gm/litre is used.
 For deep shade-60-100 gm/litre is used.

11. Alkali
Alkali is used for the following purpose-
A. Alkali is used to maintain proper pH in dye bath &
thus to create alkaline condition.
B. Alkali is used as a dye fixing agent.
C. With out alkali no dyeing will take place.
D. The strength of alkali used depend on the reactivity
of dyes.
E. As strong alkali caustic (NaOH) is used to create pH
12-12.5 when the dye is of lower reactivity.
F. As medium alkali sods ash(Na2co3) is used to create
pH 11-12. when the dye is of medium reactivity.
G. As weak alkali (NaHCO3) is used to create pH 10-
11. when the dye is of high reactivity.

12. Urea:
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.
Soaping:
By soaping the extra colour is removed from fibre surface
thus Wash fastness is improved .Soaping increases the
brightness and Stability of dye.
Chemistry of reactive dyes:
Reactive dyes differ from other colouring matters in that they
enter in to chemical reaction with fibre during dyeing & so
become a part of fibre substances. A reactive dye is
represented as R-B-X, where, RChromogen, B-Bridging
group X-Reactive system. When it reacts with fibre, F, it
forms R-B-X-F. Wet fastness of dyed material produced,
depends on stability of true covalent bond X-F.

13. A. Dyes reacting through Neucleophilic substitution reactions
(1) Di-chloro-triazynilamino
types of dyes:
These are more reactive than
mono-chloro type of dyes &
require lower temperature &
milder alkali for dyeing &
fixation. These are known as
Cold reactive dyes brand.
(2) Mono-chloro triazynylamino
type of dye:
These require higher temperature
& stronger alkali for dyeing &
fixation, are called hot brand
reactive dye.

14. (3) Mono-fluoro-triazynylamino dyes:
(4) Bis–Triazinyl dyes.
(5) Supra type of dyes.
(6) Di or tri-chloro-pyrimidylamino dyes

15. B. Dyes reacting through Neucleophilic addition reactions:
(1) Dyes containing Vinyl sulphone group:
As such this is not soluble in water, so it is marketed in its
soluble form i.e., β-hydroxy ethylene sulphone sulphuric
acid ester derivatives
RSO2 –CH2-CH2OSO3Na
(2) Dyes containing Acrylamido group:
Carbonyl group is less powerfully electron withdrawing
group & also reactivity is less as compared to vinyl
sulphone type

16. (3) α- chloro acrylamido dye:
Due to presence of chlorine atom, they are more
reactive than acrylamido dyes.

17. Chemistry behind reactive dyeing:
Dyeing principle is based on fibre reactivity & involves reaction of a functional
group of dyestuff with a site on fibre to form a covalent link between dye
molecule & substance. 4 structural feature of typical reactive dyes molecule
are:
1. Chromophoric grouping, contributing colour
2. Reactive system, enabling dye to react with hydroxy group in cellulose.
3. A bridging group that links reactive system to chromophore,
4. One or more solubilising group, usually sulphuric acid substituent
attached to chromophoric group for their colour, although Azo chromophore –
N=N- is by itself the most important.
All reactive dyes contain sodium sulphonate group for solubility & dissolve in
water to give coloured sulphonate anions & sodium cations. Most reactive dyes
have 1 to 4 of these sulphonate groups; General form of reactive dye is as
follows:
S R----B----X
• S = Water solubility group
• R = Chromophore
• X = Reactive System
• B = Bond between reactive system & Chromophore

18. Reaction between cellulose & reactive dyes:
Dyeing of cellulosic fibers with reactive dyes consists of
two phases:
 Firstly, exhaustion phase, where dye is absorbed by
material in neutral medium,
 Secondly fixation phases, where reaction between dye &
fibre takes place.

19. Control parameters of reactive dyeing:
Process parameters:
 Internal fabric pH
 Working liquor ratio on
the machine
 Effective salt
concentration (actual)
 Effective alkali
concentration (actual)
 Rate of heating
 Rate of cooling
 Fixation temperature
Raw materials:
 Man (training, understanding,
supervision)
 Water
 Common chemicals (Salt,
Alkali)
 Specialty chemicals
(Auxiliaries)
 Reactive dyestuffs

20. STAGE OF DYEING:
First stage (Dissolving of the
dye):
In this first stage, the dye, in
solid form, is equilibrated
according to the dye
dissolved in molecular form
or in micellar form
(aggregates of many
molecules with good
solubility), or in form of
dispersed micropowder
(microcrystals of dye
molecules poorly soluble)

21. Second stage (Adsorption):
During this stage, by the effect of the dye-fibre affinity, the dye is
adsorbed at the surface of the fibre, thus forming chemical bonds with
it.
Affinity, temperature, (sometimes pH and/or auxiliaries) affect the
thermodynamic interactions:
a) The balance of the reactions, thus determining the exhaustion
degree of the dyeing liquor.
b) The affinity between the dye and the fibre is the ability of both dye
and fibre to form a permanent bond. The greater the affinity, the
stronger and higher are the fibre-dye bonds and the smaller is the dye
for the solvent (water). Generally it is also directly proportional to the
molecular weight (molecular size) of the dye. Affinity is therefore a
condition strictly related to the chemical composition of the dye and
the fibre

22. A quick adsorption of the dye on the surface of the fabric
reduces the dye concentration near the fibre, thus reducing
the adsorption speed. A correct speed of the liquor change in
contact with the fibre allows the maximum concentration of
the dyeing solution near the fibre, and consequently the
correct speed.
At the same time, the liquor flow in contact with the material
is spread homogeneously and allows a good distribution of
the dye in all the areas of the textile surface; this enhances
the dye consistency with the same operating times.
The adsorption reaction is usually sufficiently quick not to
affect the dyeing speed, and often it must be slowed down or
adjusted (T°, pH, and auxiliaries) on optimum values to
avoid an irregular distribution of the dye.

23. Third stage (Diffusion):
During this stage the dye,
adsorbed in molecular form
by the surface, by breaking
and restoring the bonds
many times tends to
penetrate into the bulk of the
fibre through amorphous
areas, to spread
homogeneously and fix
steadily.
Figure: Dye concentration in the liquor near
the fibre depending on the hydrokinetic
condition

24. Fundamental factors are:
 Crystallinity of the fibre: the dyes penetrate the
fibers through amorphous areas and therefore the
higher the crystallinity, the lower the diffusion
speed.
 Molecular size of the dye: the bigger the dimensions
of the dye molecules, the more difficult the
diffusion through amorphous areas.
 Strength or dye-fibre bonds (affinity): the stronger
the bond, the more difficult the diffusion.
 Fibre makes the diffusion quicker but
simultaneously reduces the affinity and therefore
the exhaust. The presence of auxiliaries, facilitating
the fibre swelling or increasing the concentration of
dye near the fibre (swelling agents), tends to
increase the diffusion speed.
The operating time must be adequate to allow a
good penetration of the dyes, since this is a
prerequisite for developing the maximum fastness.

25. Hydrolysis of reactive dye:
Under alkaline reactive dye reacts with the terminal hydroxyl
group of cellulose. But if the solution of the dye kept for long
time its concentration drops. Then the dye react with the
hydroxyl (OH) group of water. This reaction of dye with water is
known as hydrolysis of reactive dye. After hydrolysis dye con
not react with fiber. So hydrolysis increases the loss of dyes.
Hydrolysis of halogen containing reactive dyes:
D-R-Cl + H-OH DR-OH + HCl
Hydrolysis of activated vinyl compound containing group:
D-F-CH2-CH2-OSO3H + H-OH D-F-CH2-CH2- OH + H2SO4

26. Stripping of reactive dye
 Partial stripping: Partial stripping is obtained by treating the dyed
fabric with dilute acetic acid or formic acid. Here temperature is raised to
70-100 C and treatment is continued until the shade is removed by
desired amount.
 Acetic acid -------------- 0.5 - 10 g/L
 Temperature ----------- 70 – 100 C
 Full stripping: For complete stripping the goods are first treated with
sodium hydro sulphite (Hydrose) at boil and then washed off and
bleached with 1 g/L sodium hypochlorite (NaCl) or bleaching powder at
room temperature. This is carried out as following steps-
Wetting agent ------ 0.5 – 1.0 g/L
NaOH -----------------3-6 g/L (Temp100-105 x 60-30min)
Hydrose ---------------7-10g/L
Then,
Wetting agent --------------1g/L (Room Temp x 10min)
Bleaching powder ---------1g/L

27. Influencing factors of dyeing:
 Salt.
 Soda.
 Time.
 Temperature.
 pH.
 Wetting agent.
 Sequestering agent.
 Anti-creasing agent
 Leveling agent
 All of these above are important in dyeing but we have
worked with time, temperature, and pH.

28. Effects of different parameters used in reactive dyeing:
Time:
Time is very important in dyeing. The fixation of dye depends on time. With
the increase of time the fixation of dye will increase. For example if a fabric
is dyed in a dyeing bath for five minute the amount of dye it will absorb is
less than the amount of dye will absorb by a same fabric in ten minute. As
we have worked with reactive dye so the optimum time for fixation of this
dye is sixty minute. If a fabric is dyed for sixty minute with reactive dyes it
will show all required properties, i.e. wash fastness, rubbing fastness, light
fastness, perspiration fastness etc.
Temperature:
Higher temperature causes the hydrolysis of the dye with water to become
more frequent. Experiment showed that high temperature caused the cotton
material to have a very poor ability to be dyed.
Higher temperature cause cotton material to absorb dye more because of the
molecules having more kinetic energy, thus more collision would occur
between dye molecule and fibre, increasing the chance of a reaction taking
place and bond formation.

29. pH:
In the case of most popular fiber reactive dyes, a high pH actually activates the
cellulose fiber, forming a cellulosate anion, which can then attack the dye molecule,
leading to a reaction that produces a strong, permanent covalent bond. Without a
high pH, the dye will not fix permanently to the cellulose fiber. Sodium carbonate is
used for to increase the pH of the dye reaction, so that the fiber will react with the
dye.
Color:
Color is the sensation which occurs when light enters the Eyes. It is rising from the
activity of the retina of the eye and its attached nervous mechanisms. This activity is
being, in nearly every case in the normal individual a specific response to radiant
energy of certain wavelength and intensity.
The hue refers to the actual color sensation (red, blue, yellow), the sensation or
Chroma(depth of color) to the degree of differentiation from grey(dull of vivid), and
lightness to the amount of light reflected from the object (light or dark). In the
Munsell color system, these attributes are assigned alphabetic and numerical levels.
Light:
That aspect of radiant energy of which a human observer is aware through visual
sensations arising from stimulation of the retina by the radiant energy. The
wavelength of perceived colors of visible spectral light are between 380 to 740.

30. After treatment:
•In the dyeing of deep shades or inefficient washing
equipment there may be incomplete removal of
unfixed dye.
•After treatment with cationic dye fixing agent.
•Insolubilizes the unfixed dye.
•Improves wash fastness.
•Treated with 5-10 g/L cationic dye fixing agent at
50-60º C for 10-30 mints.
•Treatment with dye fixing agent is not substitute of
wash off process.