Dyeing methods

Reactive Dyestuff | Dyeing Method of Reactive
Dye
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.
Theroy:
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.
This is shown in reactions beiow-
D-SO2-CH2-CH2-SO3Na+HO-Cell= D-SO2-CH2-CH2-O-Cell+NaHSO3
D-SO2-CH2-CH2-SO3Na+H2N-Wool= D-SO2-CH2-CH2-NH-Wool+ NaHSO3
Here,
 D=dye part
 Wool=Wool polymer.
 Cell=Cellulose polymer.
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.
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
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:
Structure of cellulose
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.
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.
Properties of reactive dye:
1. Reactive dyes are anaionic 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
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 neutralize 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.
Alkali:
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.
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.
Reactive Systems:
Reactive dyes are based on Cyanuryl chloride. Cold brand dyes (M brand) are based
on di-chloro triazinyl derivatives whereas "H" brands are mono-chloro triazinyle
derivatives. Reactivity of Chlorine atoms decreases greatly as they are successively
substituted. Thus di-chloride derivative (M) is more reactive than mono chloro
reactive (H) dyes. This is shown by fact that "M" dyes react readily with cellulose at
room temperature in presence of mild alkalis such as sodium carbonate, where as
"H" dyes need to be heated at least to 60C & require stronger alkalinity before
reaction take place at a reasonable rate. Other popular systems are based on Vinyl
suplhones & tri-chloro pyrimidyl.
Fibre-Reactive Dyes-Definition:
A fibre-reactive dye forms a covalent bond with appropriate textile functionality. It is
important that once attached, they are very difficult to remove.
A. Dyes reacting through Nucleophilic 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:
(3) Mono-fluoro-triazynylamino dyes:
(4) Bis–Triazinyl dyes.
(5) Supra type of dyes.
(6) Di or tri-chloro-pyrimidylamino dyes
B. Dyes reacting through Nucleophilic 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
(3) α- chloro acrylamido dye:
Due to presence of chlorine atom, they are more reactive than acrylamido dyes.

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
Where,
 S = Water solubility group
 R = Chromophore
 X = Reactive System
 B = Bond between reactive system & Chromophore
Reaction between Cellulose & Reactive Dyes:
Dyeing of cellulosic fibers with reactive dyes consists of two phases:
1. Firstly, exhaustion phase, where dye is absorbed by material in neutral
medium,
2. Secondly fixation phases, where reaction between dye & fibre takes place.
Cellulose in its reaction with reactive dyes is considered as alcohol. Electro
negativity of oxygen atoms governs tendency of hydroxyl group to ionize. Cellulose
is consequently ionized under alkaline conditions & can act as nucleophilic reagent &

shows subsequent reactions with acid halides (nucleophilic substitution). Mechanism
of nucleophilic substitution is as below:
Most of reactive dyes require alkaline catalyst for fixation on fibre. During dyeing with
vinyl sulphone dyes, vinyl sulphone group is formed from parent dye under alkaline
conditions, may be represented by:
Mechanism of nucleophilic addition reaction is as below:
When alkali is added to vinyl sulfone dye, it is converted to
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
Reactivity & affinity of dyes:
If reactivity of dye is increased considerably, reaction rate with fibre increases. So,

dyeing can be carried out in a very short time. However, here, dye hydrolysis rate
also increases, leading to deactivation of part of dye resulting in dye wastage. If, on
other hand, dye reactivity is decreased, extent of hydrolysis can be reduced
considerably that, how ever results in slower reaction rate with fibre also. Ultimate
dyeing object is to react as much of dye as possible with fibre with minimum dye
hydrolysis, is actually achieved in 2 stages:
 1st from aqueous medium under neutral conditions when dye does not react
with fibre or with water, Then Glauber’s salt/common salt is added to exhaust
dye onto fibre as much as possible.
 2nd step of dyeing i.e. fixation of dye on fibre is carried out by adding alkali
(usually soda ash).
Since exhausted dyes are already on fibre, it is more likely that exhausted dye reacts
with fibre in preference to water.
Method of Scouring & Bleaching:
Recipe for scouring and bleaching
 Wetting agent : 0.7 g/l
 Anti creasing agent : 0.5 g/l
 Sequestering agent : 0.7 g/l
 Stabilizer : 0.5 g/l
 Soda ash : 2.0 g/l
 H2O2 : 3.0 g/l
 L: R : 1:10
Process Curve:
Figure: Scouring bleaching with enzyme (Process curve)

Dye Bath pH:
For most of dyes optimum pH is 10.8 to 11.0 at 20-25°C soda ash is the best alkali
for dyeing at 30°C for cotton, mercerized cotton & linen. Increased fixation (due to
higher temperature) & increased dye bath stability & better reproducibility are
advantages of soda ash as fixing agent.
Dyeing Temperature:
As increase in temperature affects rate of physical & chemicals processes involved
in dyeing, it is important in reactive dyeing also. Affinity of dye for fibre decreases
with increases in temperature (dyeing is an exothermal reaction), & at same time
rate of dye hydrolysis increases, adversely affects colour yield fixation. However,
rate of diffusion of dye in fibre increases with increased temperature. At
temperatures lower than 20°C, rate of fixation is very low. Hence for most of dyes a
temperature, while for some others' dyeing at 50-60°C with sodium bicarbonate as
alkali gives maximum colour value.
Electrolyte Concentration:
Since reactive dyes have low affinity for cellulose, exhausting dye bath can increase
fixation, by adding common salt or Glauber’s salt prior to fixation. Amount of salts
required to produce adequate exhaustion decreases with decreasing liquor ratio.
Dyeing Cycle Time:
Generally, dye may be added in two portions. Salt may also be added in two lots.
Exhaustion takes place in 20-30 mins. Alkali is then added in 2 lots (also in
Progressive dosing® system developed by Hoechst) & dyeing is continued for 30-90
mins. Shade depth & dye reactivity decides dyeing time. For deeper shades, longer
times are required.
Liquor Ratio:
With increased liquor ratio, both exhaustion & fixation takes place to increased
extent. However, rate of fixation of most of dyes is not significantly affected. As liquor
ratio is decreased, effectiveness of increasing salt addition also decreases. Hence
lower amounts of salts are sufficient to get optimum exhaustion.
Dyeing of Hot Brand Reactive dyes:
In this case dye is not as reactive as cold brand dyes & hence higher temperatures

are required for achieving adequate fixation. Dye bath pH depends on dyeing
temperature, is in range of 65-80°C for cotton & viscose rayon. As with cold brand
reactive dyes, & increase in temperature generally results in weaker shades of hot
brand reactive dyes because of decreased affinity at higher temperatures &
consequent reduced fixation. Similarly lower temperatures reduce reactivity & hence
produce lower colour value unless dyeing time is prolonged or pH is increased larger
amounts of common salts or sodium sulphate should be used for exhaustion (50g/l,
75g/l for shades of up to 1%, 1-3% & above 3% respectively). Dyeing time is
generally same as in case of cold brand reactive dyes.
Finishing:
After completion of dyeing process dyed substrate, is rinsed with cold water. Then
soaping is carried out to remove hydrolysed dye present on fibre. This dye reacted
with water molecule, hence is called hydrolysed dye & remains unreacted on fibre
surface. Soaping treatment thus removes unreacted dye present on fibre thus
improving fibre brilliancy. Then few hot washes are given & with one cold wash it is
sent for drying.
How do dyes stick to fibers?
This depends on the dye and the fibre to which the dye is attached. Cotton is a
polymer with a string of glucose units joined together. Cotton is soaked in a
colourless solution of the reduced form. This is then oxidized to the blue form of
Indigo which precipitates in the fibres. Fibre reactive dyes actually form covalent
bonds with fibre molecules and are therefore extremely colour fast. A dye molecule
is reacted with the molecule trichlorotriazine: Trichlorotriazine can react with either –
OH groups (present in cotton) thus effectively bonding the dye to the fabric.
Method of Dyeing:
There are two different methods to transfer the dye from the liquor to the fibre:
Exhaust dyeing (Discontinuous systems):
The dye is dissolved or dispersed in the dyeing liquor. The material is immersed in
the dyeing liquor and is removed only when the dye has mostly transferred onto the
textile to be dyed, distributed homogeneously, well penetrated into the fibre and
fixed. At the end of the process the material is washed or rinsed to remove the
unfixed dye

Pad dyeing (Continuous or semi-continuous
systems):
This process is carried out using mechanical means (pad-batch wetting). The dyeing
liquor is distributed homogeneously onto the fabric (i.e. also the dye is distributed
homogeneously).
In a second stage the dye penetrates into the fabric and is then fixed. At the end of
the process the material is washed.
Some operations must be carried out for both
exhaust and pad dyeing:
 Dissolve or disperse the dye in water and filter.
 Achieve a homogeneous contact between the dyeing liquor and the fibre.
 Make the dye penetrate into the fibre.
 Fix the dye in the core of the fibre.
 Final washing.
Exhaust Dyeing
This process can be used for staple fibre, yarns and fabrics. The dye dissolved in the
liquor is first adsorbed, i.e. the material is dyed only on the surface (dyeing result
depends on the liquor turbulence), then penetrates in the core of the fibre (the dye
diffusion is affected by temperature and dyeing time), and finally migrates thus
allowing good dyeing uniformity and consistency (the process is affected by
operating temperature and time).
During the process, kinetic and thermodynamic reactions interact.
Dyeing Theory (exhaust dyeing):
The dyeing process is a chemical reaction occurring between the dye and the fibre:
We can examine both the kinetics (process speed) and thermodynamic (balance)
relationships

Kinetics and thermodynamics applied to dyeing:
The dyeing process is in reality a complex chemical reaction, which occurs between
the disperse dye and the fibre immersed in the solution. This process is carried out
at different process stages.
Figure: dyeing process steps
For a better understanding of the dyeing theory, it is fundamental to divide it into
several stages (even if sometimes there is a time overlapping) and study each of
them individually from various points of view:
 Kinetics (study of the reaction speed).
 Thermodynamics (study of reaction balance).
 Hydrokinetics (influence on kinetics of the liquor and/or material turbulence,
depending on the dyeing machine used). This is an important aspect not only
for exhaust dyeing.
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)

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. As far as thermodynamics aspect is concerned, the same above mentioned
criteria must be applied and in general an increase of the dyeing temperature causes
a change of the balance towards the solution dye, with a reduction of the exhaust,
and therefore a reduction of the dye-fibre affinity.
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.
Figure: Dye concentration in the liquor near the fibre depending on the hydrokinetic
condition
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.
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 and makes the diffusion quicker but simultaneously reduces the affinity
and therefore the exhaust.
Figure: Dye penetration and migration
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.
Fourth stage (Migration):
Stages 2 and 3 are reversed in this fourth migration stage; the dye must diffuse
toward the external layers of the fibre, and then come back always in solution and
migrate in areas of the fibre where there is a lower concentration of dye, thus
enhancing the colour consistency. Low affinity, poor crystallinity of the fibre, small
molecular size of the dye will favour this stage, though negatively affecting dyeing
solidity and liquor exhaustion. On the other hand, a high concentration of electrolytes
would facilitate the aggregation of anionic dyeing agents, above all in the core of the
fibre, where the dye is more concentrated, improving the exhaustion and reducing
the migration phenomenon.
Same trade name their manufacturers name and
country name.
Trade name Manufacturer Country
Procion I.C.I UK

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
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,
Cibacron Ciba Switzerland
Remazol Hoechst Germany
Levafix Bayer Germany
Reactone Geigy Switzerland
Primazin BASF

Wetting agent --------------1g/L (RoomTemp x 10min)
Bleaching powder ---------1g/L
Influencing factors of dyeing:
1. Salt.
2. Soda.
3. Time.
4. Temperature.
5. pH.
6. Wetting agent.
7. Sequestering agent.
8. Anti-creasing agent
9. Leveling agent
All of these above are important in dyeing but we have worked with time,
temperature, and pH.
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.
Higher the temperature in general increases the rate of any reaction. The same thing
occurs with dye-but also with the water that the dye is dissolved in. The dyes can
react with either the cellulose fibre or with the water, the latter reaction being known
as hydrolysis. The effect of the added energy is much greater on the dye reaction
rate than on the ability of the dye to soak into the fiber. Increasing temperature too
much cause the dye to react with the water before it ever gets into the fibre. Infact its
better to let the dye soak into the fibre for some time before beginning dye reaction
by adding soda ash (or other ph increaser) and any heat.
The cellulose molecules in cotton material can dye well at high temperature (80°c), if
the dye is already located in the fiber, adjacent to the cellulose molecules before it
react that temperature.
pH:
In the case of most popular fiber reactive dyes, a high pH actually activates the
cellulose (cotton) 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. In dyeing
cotton and other cellulose fibers with popular fiber reactive dyes such Synozol yellow
K-HL, Synozol red K3BS150%,Synozol black B 150%, sodium carbonate is used for
no other reason than to increase the pH of the dye reaction, so that the fiber will
react with the dye.
Color:
Modern concept of color was founded in 1774 by Isaac Newton.
Newton separated white day light in to a sequence of colored light call spectrum
(VIBGYOR). According to the committee of colorimetry of the optical society of
America:
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 (as
shown in table one)
Perceive color of visible spectral light:
Wavelength(nm) color
380-400 Violet
400-435 Indigo
435-480 Blue
480-490 Greenish blue
490-500 Bluish green
500-560 Green
560-580 Yellow green
580-595 Yellow
595-605 Orange
605-740 Red
Acceptable limit of color difference:
Score Evaluation Symbol
Up to 1 No color difference Right
+1 Very little color difference 0

+2 Little color difference Delta
+3 Considerable color difference X
+4 Remarkable color difference xx
Method of testing Color fastness to wash:
Color fastness to wash is very important for lab-dip. There are varieties of testing
procedure, because-
 Washing condition may vary from one country to another.
 The methods depend on the use of dyed goods.
 To evaluate repeated washing accelerated test methods are used.
The degree of fading and staining of dyed goods for washing depends upon the
following factors:
 Temperature range may be from 40-950c.
 The type and amount of detergent added to the washing bath. In many testing
procedure a standard detergent is used.
 The extent of mechanical action which can be varied by changing the
agitation speed in a washing machine or by adding steel ball to revolving the
bath.
 The washing liquor to goods ratio is 50:01
 The hardness of water
The rinsing, drying, or pressing methods used to restore the sample after the
washing test
Principle of wash fastness
A specimen (lab-dip) in contact with specified adjacent fabric or fabric or fabric is
laundered, rinsed and dried. The specimen/composite sample is treated under
appropriate condition in a chemical bath for short time. The abrasive action is
accomplished by the use of a liquor ratio and an appropriate number of steel balls.
The change in color of the specimen (dyed sample) and the staining of the adjacent
fabric is assessed by recommended Grey scale (1-5).
Apparatus and materials:

 Wash –wheel with a thermostatically controlled water bath and rating speed of
(40±2) rpm.
 Stainless steel container (capacity 55±50 ml)
 Stainless steel ball (dia=0.6cm, weight=1 gm)
 SDC, Multifibre fabric (Acetate, cotton, nylon, polyester, acrylic, wool)
 Thermometer
 Sewing machine
 Dryer
 Color matching cabinet and
 ISO Scales.
Reagents
 Reference detergent.
 Sodium Carbonate/Soda ash.
 Distilled water (Grade-3) and
 Etc.
Test specimen:
Test specimen cut a sample of dyed goods 10*4cm and sew it with same size
multifibre fabric. This is the composite test sample.
Test procedure: (ISO recommendation NO. 1-5)
ISO-105-CO1: Composite sample is treated in a wash wheel for 30 minute at (40±2)
°C with 5gm/l standard soap.

Condition for washing:
Test Temperature °C Time(minute) Steel ball Chemicals
ISO-105-CO 1 40 30 00 Soap (5g/l)
Evaluation of wash fastness:
Compare the contrast between the treated and untreated sample with Grey Scale for
changing color of dyed sample and staining of adjacent fabric in a color matching
cabinet.
Numerical rating for color changing is the shade and staining to adjacent fabric.
Number of method used.
Assessment of color fastness:
Grey Scale
Numerical rating For wash and rubbing fastness
1 Poor/ Little
2 Moderate
3 Average
4 Good
5 Excellent
Method of testing Color fastness to Rubbing:
Principle:
This test is designed to determine the degree of color which may be transferred from
the surface of a colored fabric to a specific test cloth for rubbing (dry + wet).
Equipment:
 Crock meter
 Cotton rubbing cotton
 Grey scale
 Stop watch
 Color matching cabinet
Size of fabric:
4×5 cm two pieces of sample (one warp direction/wale direction & another
weft/course direction).

Test procedure:
 Lock the test specimen onto the base of the crock meter.
 Using the spinal spring clip, set 5cm*5cm of the white cotton fabric to the
finger of the crock meter.
 Lower the covered finger on the test sample.
 Turn hand crank at the rate of one turn per second (10* 10 sec).
 Remove the white rubbing test cloth and evaluate with grey scale.
Evaluation:
Evaluation the contrast between the treated and untreated white rubbing cloth with
grey scale and rated 1-5.
Dyeing on cotton fabric with reactive dye (high
temperature method)
Recipe:
 Dye stuff --------- 4%
 Salt -------- 80 g/l
 Soda ash ----------20 g/l
 Temperature ------ 80c 90c 80c
 Time ------- 1-1.30 hrs
 Water ---------- 15 times
Procedure:
 The dye stuff are pasted with cold water and made solution at 40c
temperature
 The dye bath is set at 80c and then dye solution is added in the bath
 Fabric is immersed in the dye bath at this stage and dyeing kept running for
30 minutes
 Then salt is added in dye bath and thus the fabric kept there for 10-20
minutes.
 The temperature is raised at 90c and dyeing kept running at this stage for 10-
30 minutes and then the temperature is lowered gradually
 The dye bath is temperature is set at 80c and then soda ash is added and the
fabric kept there for 40-60 minutes

 Finally the fabric is rinsed with cold water for 10 minutes
 Then the fabric is boiled in a solution of 1-2g/l soap and 1-2g/l soda ash for
about 10 minutes
 The fabric is rinsed with warm water at 50c for about 10 minutes
 And then the fabric is neutralized with 0.5-1.0 g/l acetic acid
Read more: http://textilelearner.blogspot.com/2013/10/reactive-dyestuff-dyeing-method-
of.html#ixzz3bVTSqLVZ

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