1. VARIOUS METHODS OF
DYEING
Dr. G. SANGAMI
ASSISTANT PROFESSOR
DEPARTMENT OF CHEMISTRY
SRI RAMAKRISHNA COLLEGE OF ARTS & SCIENCE
COIMBATORE- 641 006
06.02.2025
3. Direct Dyes can be simply defined as a dye that is
soluble in water and is primarily utilized within the
textiles industry.
Direct dyes are effectively utilized to colour materials
that are made from wool, cotton, and silk.
Depends on – nature of dye and conditions of dyeing
Direct Dyes through hydrogen bonding and
electrostatic forces are attracted to the fabric material
that is being utilized.
4. Direct dyes are generally utilized by the incorporation of
spraying, immersion, and padding processes.
Direct dye is also used to dye leather, paper, and other
materials.
The primary limitation of direct dye is that it is prone to
fade and might even start to bleed colour when exposed
to sunlight or due to frequent washing.
However, it is essential to note that direct dyes are easy
to use and do not require harmful chemicals to
complete the dyeing procedure.
5. Properties of Direct Dye:
Solubility: Direct dyes are soluble in water and can be
easily applied to the fiber.
Brightness: Direct dyes offer good brightness and intense
colour.
Affinity: Direct dyes have a high affinity for cellulosic
fibers and can be easily absorbed by them.
Easy to apply: Direct dyes are easy to apply and require
simple processing.
Cost-effective: Direct dyes are relatively cheap compared
to other types of dyes.
Usage: Direct dyes are commonly used to dye cellulosic
fibers such as cotton, rayon, and paper.
6. DYE BATH - PREPARATION
Dye in cold water
Sodium sulphate and
sulphuric acid or
Acetic acid
Material is
introduced in dye
bath T-60˚C
Common salt or
Glauber’s salt
Material is rinsed and
dried
7. Washing fastness is improved by following treatments
1. Development with diazonium salts
2. Diazotisation and development
3. Treatment with chromium fluoride or sulphate
4. Treatment with formaldehyde
5. Treatment with copper salts
Useful in
modifying the
shade of the
dyed fibre
8. Cotton, Linen and Rayon- do not show affinity for many dyes that
are used for wool and silk.
So, they can be dyed with direct dyeing method.
Steps :
Dye is dissolved in hot water.
5-20% of sodium sulphate & 0.5- 2% Sodium carborane are
added.
Now fibres are introduced in dyeing bath at 50-60˚C and then
raised to 85-95 ˚C.
Dyeing is completed in 1 hour.
10. The word vat means, ‘Vessel’.
The dyes take their name from vatting.
The vat dyes are naturally coloring matter and kept
in wooden vat and make solubilise vat dyes by the
process of fermentation – so it is called vat dye.
Properties
Vat dyes are natural colouring dyes.
Vat dye is water insoluble and can’t be applied
directly on textile material.
Vatting process is needed for making the insoluble
vat dyes into soluble form.
11. Vat dyes retain C=O chromophore in structure, which
renders water insolubility.
These are water-insoluble dyes and cannot be used
on fabrics directly.
vat dyes require a vatting process which involves
the conversion of water-insoluble dyes into water-
soluble leuco form.
During the vatting process, reducing agents such
as sodium hydrosulfite and sodium hydroxide are
added.
12. DYE BATH PREPARATION – VAT DYE
DYE (Form of paste with water)
Water containing caustic soda and
Hydrosulphite
Water
Cotton cloth is impregnated in the above vat
liquor
Steaming process (proper fixation of leuco
compound to the fabric)
Bath containing oxidising agents (Chromate,
acetic acid or perchlorate)
Generation of Colour
Soaped, rinsed and dried
1
2
3
4
5
6
7
14. The vat dyes have excellent light fastness due to
stable electron arrangement in the chromophore
(colour-bearing group) of the dye molecule and
presence of numerous benzene rings.
Vat dyes have excellent wash fastness owing to the
aqueous insolubility of the oxidized dye absorbed in
the fiber and due to large vat dye molecules trapped
within the polymer system.
However, vat dyes are usually very expensive and
need more expertise for their application because of
greater number of steps involved in dyeing.
USES
16. A mordant or dye fixative is a substance used to set
(i.e., bind) dyes on fabrics.
It does this by forming a coordination complex with
the dye, which then attaches to the fabric (or tissue).
It may be used for dyeing fabrics or for
intensifying stains in cell or tissue preparations.
Although mordants are still used, especially by small
batch dyers, it has been largely displaced in industry
by directs.
17. Mordant red 19 is a typical mordant dye.
Like many mordant dyes, it features the azo group (RN=NR)
and various sites for chelating to metal cations.
Example:
18. Common dye mordants
Tannic acid
oxalic acid
Alum
chrome alum
sodium chloride and
certain salts of aluminium, chromium, copper, iron,
iodine, potassium, sodium, tungsten and tin.
19. PROPERTIES OF MORDANT DYES
Mordant dyes - Economical dyes and are used to
produce dark green, blue and blacks.
Good levelling and colour fastness properties.
The interaction between fibre and dye is established
through strong ionic bonds which are formed between
the anionic group of colourant and ammonium cations
on the fibres.
Chromium or metal ion acts as bridge between dye
and the fibre which gives strong linkage and excellent
fastness properties.
20. Whenever mordant dyes are applied– Pretreatment of the
fibre is most important.
The mordant becomes attached to the fibre and then
combines with the dye to form an insoluble complex called a
LAKE.
Eg.
Mordant- Aluminium hydroxide
Aluminium hydroxide gets precipitated in the cotton fibre.
When Alizarin (dye) is added, this mordant binds to it and
forms Aluminium lake.
21. DYE BATH PREPARATION- MORDANT DYE
Dye+2-5% acetic acid and 10% of sodium
sulphate
Temperature is maintained at 50-60˚C
Fibre is introduced in to dye bath
Temperature is raised to boil till uniformity is
attained
Temperature is dropped and sodium dichromate (1/2 the
weight of dye) is added
Rinsed and dried
Step: 1
Step: 2
Step: 3
Step: 4
Step: 5
Step: 6
23. The term ‘Disperse dye’ is an organic colouring
substance which is free from ionizing group are of
low water solubility and are suitable for dyeing
hydrophobic textile materials.
It has low molecular weight and derivatives of
Azo, Anthra – quinine, Di phenyline amine and other
components.
It is used for dyeing polyester fibres.
Developed from cellulose acetate and polyamide
fibres.
24. PROPERTIES OF DISPERSE DYES
Disperse dyes are non-ionic dyes. So they are free
from ionizing group.
They are ready made dyes and are insoluble in water
or have very low water solubility.
They are organic colouring substances which are
suitable for dyeing hydrophobic fibres.
25. Disperse dyes are used for dyeing man made cellulose
ester and synthetic fibres specially acetate and polyester
fibres and sometimes nylon and acrylic fibres.
Carrier or dispersing agents are required for dyeing
with disperse dyes.
Disperse dyes have fair to good light fastness with
rating about 4-5.
The wash fastness of these dyes is moderate to good
with rating about 3-4.
Of all dyestuffs disperse dyes are of smallest molecular
size.
26. METHOD OF APPLICATION
Dye is pasted on the fibre at 40˚C
Dispersing agent and carrier are added
to the dye bath
Carrier- Trichlorobenzene, biphenyl
or o-phenyl phenol
Temperature- 80 ˚C
Alternate process- Thermosol process
Sublimation (Vaporisation)
Finishing
Finishing
1
2
3
4
28. Azo dyes are organic compounds bearing
the functional group R−N=N−R , in which R and R
′ ′
are usually aryl and substituted aryl groups. They
are a commercially important family of azo
compounds, i.e. compounds containing the C-N=N-
C linkage.
Azo dyes are synthetic dyes and do not occur
naturally.
Most azo dyes contain only one azo group but
there are some that contain two or three azo
groups, called "diazo dyes" and "triazo dyes"
respectively.
29. Azo dyes comprise 60-70% of all dyes used
in food and textile industries.
Azo dyes are widely used to treat textiles, leather articles, and
some foods.
There are about 2000 kinds of azoic dyes on the market.
The dyes containing azo groups – N = N – are called Azoic Dye.
These are not ready made dyes but are produced by reaction of
two components – Diazocomponent or Base/Salt and coupling
component (Napthol).
Dye formation in fiber occurs on the basis of coupling reaction.
31. PROPERTIES
Light fastness property is admirable.
Brightness of shade is also admirable.
It is insoluble in water.
These dye stuffs are always used in dyeing cellulosic
material.
Here dyeing operation is completed by two bath
arrangement. One is called impregnation bath and another is
called developing bath.
Suitable for lighter shade dyeing.
32. Two bath of individual recipe is used for dyeing with azo dyes.
Impregnation Bath.
Developing Bath.
USES
Firstly, the color fastness of the azoic color is good.
Secondly, it has a wide color range.
Thereafter, it has a versatile application area.
Moreover, it is cost-effective than other dyes.
It is compatible to use with different dyeing, and printing
techniques.
Also, it has the ability to absorb light.
Lastly, the environmental impact is low.
34. The term “acid dye” derives from the dyeing process, which is
carried out in an acidic aqueous solution (pH 2.6).
Acid dyestuff is so called mainly due to two reasons.
In the first place these classes of dyestuff were applied in a bath
containing mineral or organic acids like sulphuric, acetic or formic
acid and secondly most of them are sodium salts of organics acids.
They are commonly used for dyeing protein fibers (e. g. wool and
silk) and nylon fibers.
Acid dyes are anionic in nature, and their negatively charged
anions are attracted by positively charged amino groups in wool
under acidic conditions.
35. A common property of these dyes is their mechanism of interaction
with the fiber polymers, which leads to strong binding of the dye to
the material.
The binding of the dye at least partly can be understood to follow
an ion exchange mechanism.
Ionic bonds are formed between charged groups present in the
fiber polymer and the charged dyestuff molecule.
The dyes are important for coloration of protein fibers (wool, silk)
and polyamides, which contain ammonium groups at low pH.
These cationic groups serve as binding anchor to build an ionic
bonding with negatively charged groups, for example, sulphonate
groups in the acid dye and metal complex dye.
37. To achieve water solubility of the dye
To build an ionic bond linkage to the fiber
Besides the ionic bond, also secondary attractive forces (Van der
Waals forces) contribute to strengthening of the dyestuff–fiber
interaction.
38. Properties of acid dyes
Acid dyestuff is soluble in water.
These dyes are anionic in nature.
They are usually combined with basic dyes.
These dyes are suitable for wool, silk, polyamide and modified
acrylics.
These dyes are generally applied in the presence of acids like
sulphuric, acetic or formic acid to neutral pH bath.
These dyes have no affinity for cotton cellulose hence not suitable
for cellulosics.
They have substantivity towards protein and polyamide fibers.
These dyes combine with the fiber by hydrogen bonds, vander
waals forces or through ionic linkages.
The dyed acid colors have good light fastness and
moderate washing fastness.
39. DYE BATH PREPARATION- ACID DYES
DYE in cold water
Small qty of sodium sulphate and sulphuric or
acetic acid
Fibre is introduced in to the dye
bath
Temperature is gradually
increased
Dyeing is completed at boiling
temperature (one and half hours)
Rinsed and dried
41. A dye, which is capable of reacting chemically with a
substrate to form a covalent dye substrate linkage, is
known as reactive dyes.
The reactive dyes constitute the most commonly used
class of dyes for dyeing cellulosic textiles, because of
their good all-round properties, such as water solubility,
ease of application, variety of application methods,
availability of different shades, brightness of color
shades, good to excellent wash and light fastness and
moderate price.
Reactive dyes may have poor fastness to chlorine bleach.
42. 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 of cellulosic fibres on between the
dye molecules and the terminal –NH2 (amino) group of polyamide
or wool fibres.
Fibresdyed
Cotton, rayon, flax and other cellulosic fibres.
Polyamide and wool fibres.
Silk and acetate fibres.
43. Dyeing methods employed
Impregnation by padding
Dyeing in the dye bath
First method
Dye is dissolved in one vessel
Wetting agent- sod.sulphate and sod.
bicarbonate----in another vessel
Mixing these 2 solutions
Cotton fabric is padded and dyed
above 100˚C
Function of bicarbonate- is to yield alkali which fixes the reactive dye on the fabric.
Function of Sodium sulphate- is to prevent the movement of the dye during drying.
44. SECOND METHOD
Dyeing with certain reactive dyes (2-3%) of the dye
+
High concentration of common salt
USES
Medical Industry
Food Industry
Leather Colouration
Dyeing of Fur Skins
Dyeing of Double Weave Cloths
Wood Staining and Coating
Ink Formulation
Jute Dyeing
