Dyeing is the process of adding color
to textile products like fibers, yarns, and fabrics.
Dyeing is normally done in a special solution
containing dyes & particular chemical material.
After dyeing, dye molecules have uncut chemical
bond with fiber molecules. The temperature and
time controlling are two key factors in dyeing.
There are mainly two classes of dyes,
natural and man-made.
The first synthetic dye was William Perkin's mauveine in 1856, derived from coal
tar. Alizarin, the red dye present in madder, was the first natural pigment to be
duplicated synthetically in 1869
The earliest surviving evidence of textile dyeing was found at the large Anatolia,
where traces of red dyes, possibly from ochre, an iron oxide pigment derived
from clay, were found In China.
Dyeing with plants, barks, and insects been traced back more than 5,000 years.
Early evidence of dyeing comes from Sindh province in Pakistan, where a piece of
cotton dyed with a vegetable dye was recovered from the Archaeological site
at Mohenjo-Daro (3rd millennium BCE)
Natural insect dyes such as Tyrian purple and kermes
plant-based dyes such as woad, indigo and madder
(a) Spray coating methods,
e.g Wurster air suspension Coating
(b) Wall deposition from solution,
e.g. coacervation or phase separation
(c) Interfacial reaction
(d) Physical processes,
e.g. annular jet encapsulation
(e) Matrix solidification,
e.g. spray drying or chilling
(f)Naturally occuring microcapsules
Microencapsulation of Disperse dye
CI Disperse Blue 56 (1)
CI Disperse Red 60 (2)
Microencapsulation of Acid dyes
These will be discussed briefly:
Dyeing of polyester requires water and certain chemical auxiliaries such as
dispersing agents, penetrating agents and levelling agents, in the dye bath.
Unfortunately, residual auxiliaries and dyestuff may be present in the effluent and
may cause pollution.
Polyester fabric was dyed with microencapsulated CI Disperse Blue 56 using a high
temperature dyeing process without dispersing agents, penetrating agents, levelling
agents or other auxiliaries. The quality of the polyester fabric dyed in this manner
without reduction clearing was at least as good as that dyed traditionally
Microencapsulation of disperse dyes provides the
opportunity to carry out dyeing in absence of
auxiliaries and without dyeing without affecting other
Different disperse dyes having different dyeing
behavior can be make to behave similarly by
microencapsulation. So this technique is a very useful
tool in compound shade dyeing.
Microencapsulation of acid dyes can be used for
improving leveling. This can also be used improve
barre dyeing. As this technique retard the rate of
dyeing it can be used successfully.
A novel electrochemical dyeing
process results in product savings,
less chemicals with special safety
requirements, and unsurpassed
Besides, the new process also
facilitates dye bath monitoring in
real time, ensuring high quality of
the dyed fabric
Indigo, vat dyes and sulphur dyes are an important class of
dyestuffs for dyeing cellulosic fibres.
These dyes are applied to different varieties of products
but the application procedure contains a common
reduction step with strong reducing agents to attain the
reduced form of dyestuff.
According to the dyeing procedure and nature of dye,
different reducing agents are used
These chemicals produce toxic nature by-products, which
are acidic in nature
These agents is used in dye reduction and the excess
chemicals find their way into the waste water. By-
products formed in the decomposition of hydrosulfite
are sulphur compounds (eg, Na2S, NaHS, etc).
which pollute the atmosphere through the formation
At the same time, salts of sulphur in form of sulphates
and sulphites (Na2SO3, NaHSO4, Na2SO4, Na2S2O3,
Electrochemical dyeing process results
less chemicals with special safety
better fastness properties.
In case of direct electrochemical dyeing technique,
organic dyestuff has been directly reduced by contact
between dye and electrode.
In this system, the dye reduction does not take place due
to direct contact of dyestuff with the cathode, like in
direct electrochemical reduction.
The dye is not directly reduced at the electrode rather, a
reducing agent is added that reduces the dye in the
conventional manner, which in turn gets oxidized after
The electrolysis is carried out under galvanostatic
condition by maintaining the constant current.
The pre-treated fabric sample is introduced into
the dye bath.
The dyeing is carried out by exhaustion method
for 30 minutes with constant stirring. Both
electrolysis and electrochemical dyeing are
carried out at 300 ± 2 K.
After completion of dyeing, the fabric sample was
washed with cold water and exposed to air, for
oxidation/fixation of dye molecules.
Then the fabric was soaped at boil, rinsed with
cold water, and air dried
The entire textile industry gets affected because savings in
the chemical costs as chemical wastes are reduced by 80%.
Reduction of waste water recycling cost at the same time
water savings around 85%,
Electrode material for cathode and anode is cheap.
simply constructed cell and easy maintenance, so
Several times bath recycling is possible with this dyeing
The toxic nature sulphates and sulphites are not there in
effluent so no adverse effect on aquatic life.
Low concentration of chemicals and non-toxic chemicals.
Economic technique for recycling of chemicals and water
used for washing
Fully controlled dyeing parameters.
Maximum process reliability through control of reducing potential as
needed ranging from 0 to 1,200 mV just by varying the current.
Dye reduction rate is very good (10 mg dye/min)
Dye pick up may go up to 85 - 90%.
Better overall fastness property compared with the technique already in
Reproducible process condition.
Dyeing results was observed.
Better quality product. [
The results obtained convey the conclusion that
reducing agents required in the dyeing process for vat
and sulphur dyes cannot be recycled, and lead to
problematic waste products.
Therefore, modern economical and ecological
requirements are not fulfilled.
The final results are similar to those obtained in
dyeing with chemical reducing agents. Improvements
in control of the dyeing process can be anticipated, as
well as environmental benefits and saving in process