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 CountryProcion I.C.I UK

Cibacron Ciba SwitzerlandRemazol Hoechst GermanyLevafix Bayer GermanyReactone Geigy SwitzerlandPrimazin BASF

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, 

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 ChemicalsISO-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 ScaleNumerical rating For wash and rubbing fastness

1                     Poor/ Little2                     Moderate3                     Average4                     Good5                     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