Reactive Dyes: Classification, Dyeing Mechanism, Application & Stripping

Introduction:
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.

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.

Reaction:

D-SO2-CH2-CH2-OSO3Na +OH-cell    →       D-SO2-CH2-CH2-O-cell + NaHSO3

D-SO2-CH2-CH2-OSO3Na + NH2– wool    →   D-SO2-CH2-CH2-NH-Wool + NaHSO3

Here,
D= dye part.
Wool = wool polymer.
Cell = cellulosic polymer.

Why reactive dye is so called?
Reactive dyes are so called because this is the only type of dye, which has reactive group, and that reactive group reacts chemically with fibre polymer molecules and form covalent bond. This covalent bond is formed between the reactive group and terminal –OH (Hydroxyl) group of cellulosic fibre and wool fiber or between reactive group and terminal -NH2 (Amino) group of polyamide polymer. The strength of this covalent bond is more than ionic bond, hydrogen bond and Vander Waal’s force of attraction. Thus the reactive group becomes an integral part of the fibre.

For this reasons the dyes are so called. They are also called ‘fibre reactive group’.

History:
On the occasion of 100 year’s celebration of synthetic dyes manufacturing, two chemists of ICI company (UK) named Stephen and Rattee tried to manufacture a new dyestuff. Thus they succeed to invent a new dye in 1965, which was named REACTIVE DYE. This was manufacture for dyeing cellulosic fabrics. The first three reactive dyes were PROCION YELLOWR, PROCION BRILLIANT RED 2B and PROCION BLUE 3G for this effort they were awarded gold medal of the society of dyes and colorists for the year 1960.

Fibres dyed:
By reactive dyes the following fibres can be dyed successfully:

  1. Cotton, rayon, flax and other cellulosic fibres.
  2. Polyamide and wool fibres.
  3. Silk and acetate fibres.

It covers a wide range of color spectrum and includes shades varying from bright to heavy dark like,

  • Violet
  • Blue
  • Green
  • Red
  • Black
  • Yellow ctc.

Trade names of reactive dye:
Some trade names of this dye are mentioned:

Trade name Manufacturer Country
Procion I.C.I U.K
Ciba cron Ciba Switzerland
Remazol Hoechst Germany
Levafix Bayer Germany
Reactone Geigy Switzerland
Primazin BASF Germany
Drimarine Sandoz Switzerland

Popularity of reactive dye:
Reactive are mostly used for dyeing cellulosic fibres. At past cellulosic fibres were dyed with direct and vat dyes, but after the introduction of reactive dyes there utility has become limited. Reactive dyes are superior to direct dye in the following aspects:

  1. Ability to procedure bright shades of wide range.
  2. High leveling quality.
  3. Good washing fastness.
  4. Good light fastness.

And it is superior to vat dyes in the following aspects:

  1. Simple dyeing method therefore one stage dyeing.
  2. Low temperature dyeing (below 1000C)
  3. Lower cost, i.e. cheaper.

Again its dyeing process is fast and gives brighter shades than metallized azo dyes. For the above reasons reactive dyes are more popular.

Properties or Characteristics of reactive dye:

  1. Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibres.
  2. Reactive dyes are found in power, liquid and print paste form.
  3. During dyeing the reactive group of this dye forms covalent bond with fibre polymer and becomes an integral parts of the fibre.
  4. Reactive dyes are soluble in water.
  5. They have very good light fastness with rating about 6. The dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.
  6. Textile materials dyed with reactive dyes have very good wash fastness with rating about 4-5 due to strong covalent bonds formed between fibre polymer and reactive group of dye.
  7. Reactive dye gives brighter shades and has moderate rubbing fastness.
  8. Dyeing method of reactive dyes is easy. It requires less time and low temperature for dyeing.
  9. Reactive dyes are comparatively cheap
  10. Reactive dyes have good perspiration fastness with rating 4-5.
  11. Reactive dyes have good perspiration fastness.

General structure of reactive dyes:
The general structure of reactive dye is: D-B-G-X.

Chemical structure of reactive dyes
Fig: Chemical structure of reactive dyes

Here,
D = Dye part or chromogen (color producing part).
Dyes may be direct, acid, disperse, premetallised dye etc.

B = Bridging part.
Bridging part may be –NH- group or –NR- group.

G = Reactive group bearing part.

X= reactive group.

Classification of reactive dyes:
Reactive dyes may be classified in various ways as below:

A. On the basis of reactive group:

a. Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-

  1. Triazine group
  2. Pyridimine group
  3. Quinoxaline dyes

Example:

  • Triazine derivatives: procion, cibacron.
  • Pyridimine derivatives: reactone
  • Quinoxaline derivatives: levafix.

b. Activated vinyl compound:

  1. Vinyl sulphone
  2. Vinyl acrylamide
  3. Vinyl sulphonamide.

Example:

  • Vinyl sulphone: remazol
  • Vinyl acrylamide: primazine
  • Vinyl sulphonamide: levafix.

B. On the basis of reactivity:

  1. Lower reactive dye: Here pH is maintained 12-12.5 by using NaOH in bath.
  2. Medium reactive dye: here pH is maintained 11-12 by using Na2CO3 in dye bath.
  3. Higher reactive dye: here pH is maintained 10-11 by using NaHCO3 in dye bath.

C. On the basis of dyeing temperature:

a. Cold brand:
These types of dyes contain reactive group of high reactivity. So dyeing can be done in lower temperature i.e. 320-600C.

For example: PROCION M, LIVAFIX E.

b. Medium brand:
This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.

For example, Remazol, Livafix are medium brand dyes.

c. Hot brand:
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930C temperature is required for dyeing.

For example PRICION H, CIBACRON are hot brand dyes.

Characteristics of reactive group of reactive dye:

  1. The characteristics of reactive group of dye are mentioned below:
  2. Reactive groups do not contribute to the color of dye. Chromogen group imparts it.
  3. The reactivity of vinyl sulphone group is less than that of halogen group.
  4. If no of reactive group increases, binding also increases depending on dye structure.
  5. Reactive dye absorb up to 90%.
  6. Molecular weight of reactive group 69-211gm/ mole.
  7. Bond energy of halogen groups are as below:
    • F (Fluorine)- 102-kcal/ gm
    • Cl (chlorine) – 74-kcal/ gm
    • Br (bromine) – 64-kcal/ gm
    • I (iodine) – 56-kcal/ gm
  8. If the molecular weight of reactive group increases, reactivity also increases.
  9. Reactivity of iodine is high but tits rate of hydrolysis is also high.
  10. Chlorine imparts medium reactivity, but it is cheap and hydrolysis rate is medium.
  11. Reactivity of fluorine is the least and its rate hydrolysis is also less.
  12. Reactivity of vinyl sulphone group increases with increasing temperature and pH.
  13. Sulphone group has more solubility but it is not stable.
  14. Generally low molecular weight dyes are of hot brand.
  15. Less affinity dyes are used for pad method.

Assistants used for dyeing with reactive dyes:
The following assistants are used in dye bath for dyeing with reactive dyes.

Salt:
As a salt NaCl is used widely. The salts do the following things-

  • Salts are used to increase the affinity of dye to fibre.
  • It decreases the hydrolysis rate of dyes.
  • It neutralizes the electro negativity of fibre surface when immersed in solution.
  • It puts extra energy to push the dye inside the fibre polymer i.e. increase absorption of dye.

The amount of salt and used depends upon the shade to be produced.

  • For light shade – 10gm/ L salt is used.
  • For medium shade – 20 gm/ L salt is used.
  • For dark shade – 30gm/L salt is used.

Alkali:
Alkali is used for the following purposes:

  • Alkali is used to maintain proper pH in dye bath and thus to create alkaline condition.
  • Alkali is used as a dye-fixing agent.
  • Without alkali no dyeing take place.
  • The strength of alkali used depends on the reactivity of dyes.
  • As strong alkali caustic soda is used to create pH 12.5-12.
  • As medium alkali soda ash (Na2CO3) is used to create pH 11-12 when dye is of medium reactivity.
  • As weak alkali NaHCO3 is used to create pH 10-11 when dye is highly reactive.

Urea:
Urea is used in continuous method of dying. It helps to get required shade of dye. To get dark shade more urea is used and to get light shade less amount of urea is used.

Soaping:
By soaping, the extra color is removed from fibre surface. Thus washing fastness is improved. Soaping increases the brightness and stability of the dye.

Factors considered for selection of dyes:
Dye selection depends upon the following factors:

1. Selection of dying method: Dye selection depends on dyeing method, which may be:

  1. Batch wise/ discontinuous method
  2. Semi-continuous method i.e.
    • Pad – batch method
    • Pad – jig method
    • Pad – roll method
  3. Continuous method i.e.
    • Pad – steam method
    • Pad – dry method
    • Pad – thermo fix method

This dyeing method selection depends on:

  1. Speed of dye diffusion on the fibre.
  2. Affinity of dye to fibre
  3. Reactivity to dye stuff.

2. Selection of brand: Brand selection is important. It may be

  1. Hot brand – Less reactive dye (temp 72-93)
  2. Medium brand – Medium reactive dye.
  3. Cold brand – Most reactive dye.

3. Economy of production

4. Availability of dyes

5. Storage of dyes.

6. Bond stability i.e. kind of bonding

7. Fastness of dye i.e. washes, light, rubbing fastness

8. Re – producibility

Reaction manner of dye and cellulose:
The bonding behavior of dye and cellulose are mentioned below:

  1. Hydroxyl group of cotton polymer takes part in reaction with reactive group of dye
  2. Reactive group of dye react preferably with the hydroxyl group of cellulose than that of water.
  3. The activation energy of dye – water reaction is 16.4 – 26.2 kcal and that of dye cellulose is 9.2 – 15.8 kcal. As the latter is less, so that occurs predominately.
  4. Higher activation energy causes slower reaction.
  5. The reaction with water and dye takes place in a smaller extent.
  6. The strength of covalent bond formed between cellulose polymer and reactive group is more than hydrogen bonding, vander wall’s force of attraction and metal co-ordination bonds.
  7. Extreme acidic and alkaline condition should be avoided, otherwise hydrolysis will take place resulting bond breakage and poor wash fastness.

Criteria for cellulose for attracting reactive dye:
The chemical structure of cellulose macromolecule is given below:

In cellulose macromolecule glucose units are linked through oxygen bridges formed between C1 position of one glucose and C4 position of adjacent glucose unit. Each glucose unit contains one primary hydroxyl group (at C6 position) and two secondary hydroxyl group =CHOH (at C2 and C3 positions). Again one end of this glucose unit has an additional secondary hydroxyl group at C4 position and the other end has an aldehyde or hemiacetal group at C1 position.

Now the following things are considered:

  • Primary hydroxyl group (-CH2OH) at C6 position is more reactive then the secondary hydroxyl groups (-CHOH) at C2 and C3 positions.
  • C2 hydroxyl group is supported to be more acidic than C3 hydroxyl group under suitable alkaline condition and hence is more reactive.
  • The hemiacetal group at C1 position is the most active while the additional hydroxyl group of C4 position is the least reactive.
  • The reaction between reactive group and cellulose takes place predominantly with primary hydroxyl group to some extent.
  • Longer carbon chain lowers the rate of reaction.
  • Incase of monochloro triazinyl dyes, this reaction takes place 15 times more frequently with C6 hydroxyl group than with the hydroxyl group at C2 or C3 position.
  • In case of dichlorotriazinyl dyes, this reaction takes place 3-7 times more frequently with hydroxyl group at C2 position than that with hydroxyl group at C1 or C3 position.

The reactive rate of some compounds are mentioned below:

COMPOUND                         STRUCTURE                         REACTIVE RATE

  • Water                              H-OH                                             1.0
  • Iso-propanol                   CH3-CHOH-CH3                            0.7
  • Ethanol                           CH3-CH2-OH                                  7.4
  • Methanol                        H-CH2-OH                                      12.3
  • Glucose                           C6H12O6                                        5.5

So from the above table it is obvious that secondary hydroxyl group is the beast reactive while primary one is the most reactive.

Dyeing mechanism of reactive dye:
The dyeing mechanism of material with reactive dye takes place in 3 stages:-

  1. Exhaustion of dye in presence of electrolyte or dye absorption.
  2. Fixation under the influence of alkali.
  3. wash-off the unfixed dye from material surface.

Now they are mentioned below:

1. Dye absorption:
When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize the negative charge formed in the fibre surface and puts extra energy to increase dye absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.

2. Fixation:
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fibre and thus forming strong covalent bond with the fibre and thus forming strong covalent bond with the fibre. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this purpose depends on brand of dye and dyeing temperature. Here generally caustic soda, soda ash or NaHCO3 is used as alkali depending upon reactivity of dye. They create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below:

………………………………………………………….Alkali
D-SO2-CH2-CH2-OSO3Na + OH-Cell —————→ D-SO2-CH2-CH2-O-Cell + NaHSO3
………………………………………………………pH 10-12.5

……………………………………………………………Alkali
D-SO2-CH2-CH2-OSO3Na + OH-Wool ————-→ D-SO2-CH2-CH2-O-Wool + NaHSO3
………………………………………………………..pH 10-12.5

reaction of reactive dye

3. Wash-off:
As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Application method of reactive dyes:
Application method of reactive dyes varies significantly with type of dyes, shade required, and available equipments in the mill. These are 3 application procedures available:

1. Discontinuous method-

  • Conventional method
  • Exhaust or constant temperature method
  • High temperature method
  • Hot critical method.

2. Cotinuous method-

  • Pad-steam method
  • Pad dry method
  • Pad thermofix method

3. Semi continuous method-

  • Pad roll method
  • Pad jig method
  • Pad batch method.

Stripping of reactive dye:
The reactive dye cannot be satisfactory stripped from fibre due to covalent bond between dye molecule and fibre. Stripping becomes necessary when uneven dyeing occurs.  By stripping azo group (–N=N–) from the dye is removed. Now the stripping processes are described:-

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 shade is removed by desired amount. After that a through washing is necessary to remove the product of hydrolysis. The amount of acid used is as below: –

  • Glacial acetic acid       : 5-10 parts
  • With water                 :1000 parts

Or

  • Formic acid                       : 2.5 to 10 parts
  • With water                        : 1000 parts
  • Temperature                     : 70 – 100°C
  • Time                                   : until desired shade is obtained.

Full stripping:
For complete stripping the goods are first treated with sodium hydrosulphite (hydrose) at boil then washed off and bleached with 1% sodium hypochlorite (NaOCl) at room temperature. This is carried out for 30 min.

The recipe is as below:

  • Na-hypochlorite : 1% at room temperature
  • Na-hydrosulpite: at boil.
  • Time                  : 30 min

Hydrolysis of reactive dye:
Under alkaline condition reactive dyes react with the terminal hydroxyl group of cellulose. But if the solution of the dye is kept for long time its concentration drops. Then the dye react with the hydroxyl group of water. This reaction of dye with water is known as hydrolysis of reactive dye. After hydrolysis dye cannot react with fibre. So hydrolysis increases the loss of dyes.

This hydrolysis occurs in two stages. At first the concentration of dye initially increases and then begins to decrease. Where as the concentration of hydroxyl compound increases continuously. Then the hydroxyl compound cannot react with dye.

1. Hydrolysis of halogen containing reactive dye,

D-R-Cl  +  H-OH                 →                     D-R-OH  +  H-Cl

2. Hydrolysis of activated vinyl compound containing dye,

D-F-CH2-CH2-OSO3H  +  H-OH          →        D-F- CH2-CH2-OH + H2SO4

For preventing hydrolysis the following precautions are taken—

  • As hydrolysis increases with increasing temperature during dissolving and application temperature should not be more than 40°C.
  • Dye and alkali solution are prepared separately and mixed just before using.
  • Dye and alkali should not be kept for long time after mixing.

Important factors for dyeing cellulosic fibre with cold brand reactive dye in batching process:
The important factors are as follows:

1) pH of the dye bath:
The optimum pH for fixing cold brand reactive dyes on cotton and viscose rayon depends on individual dyes, the temperature and time of dyeing. pH decreases with increasing temperature and time of dyeing. For most of the dyes the optimum pH is 10.8 to 11 at 20o to 25oC. Soda ash has been the best alkali for dyeing at 30oC for cotton, mercerized cotton and linen. Increased fixation (due to higher temperature) and increased dye bath stability and better reproducibility are the advantages of soda ash as the fixing agent.

For viscose rayon the optimum pH is 10.3 at 20o to 25oC.

2) Amount of Alkali:
The amount of alkali used for fixing depends on the depth of shade dyed and the liquor ratio employed. Some quantities of alkali required for fixing the reactive dyes are given table 28.

3) Dyeing temperature:
Since increase in temperature affects the rate of physical and chemical processes involved in dyeing, it is important in dyeing reactive dyes also. The affinity of the dye for the fibre decreases with increases in temperature and at the same time the rate of hydrolysis of the dye increases and adversely affects the fixation of color yield. However the rate of diffusion of the dye in the fibre increases with increased temperature. At temperatures lower than 20oc, the rate of fixation is very low. Hence for most of the dyes a temperature of 20o to 25oC is the recommended temperature while for some other dyeing at 50o to 60oC with sodium bicarbonate as the alkali gives maximum color value.

4) Electrolyte concentration:
Since reactive dyes have low affinity for cellulose exhausting the dye bath by adding common salt or Glauber’s salt prior to fixation can increase the fixation. The amount of salt required producing adequate exhaustion decreases with decreasing liquor ratio. Thus for pale shade on cotton and viscose rayon 15 and 10 g/l of common salt used. The quantities may be increased to 30 and 20 to 30 g/l for medium and deep shades on these fibres.

5) Time of dyeing:
Generally the dye may be added in two portions. The salt may also be added in two lots. The exhaustion takes place in 20 to 30 min. There is generally no advantage in extending the period beyond 30 min. The alkali is then added and the dyeing continued for 30 to 90 min. The depth of shade and reactivity of the dye decide the time of dyeing. For deeper shades larger times are required.

6) Liquor ratio:
With decreased liquor ratio, both exhaustion and fixation take place to increased exert. However the rate of fixation of most of the dyes is not significantly affected. As the liquor ratio is decreased, the effectiveness of increasing salt addition also decreases. Hence lower amount of salt are sufficient to get optimum exhaustion.

Why low affinity reactive dyes are preferred for dyeing?
If the reactivity of the dye is increased considerably, the rate of reaction with the fibre increases. There fore, the dyeing can be carried out in a short time. However in this case the rate of dye also increases, leading to deactivation of a part of the dye. This results in   wastage of the dye. If on the other hand the reactivity of the dye is decreased, the extent of hydrolysis can be reduced considerably.

However this results in the slower rate of reaction with the fibre also. The ultimate object of dyeing is to react as much of the dye ass possible with the fibre and minimize the hydrolysis of the dye. This is achieved in practice in two stages. The dyeing is first started from the aqueous medium under neutral conditions when the dye does not react either with the fibre or with water. Then gluber salt or common salt is added to exhaust the dye onto the fibre as much as possible. In this respect, this stage of dyeing (exhaustion) resembles the dyeing of direct dyes on cotton. Then the second step (that of fixation or reaction with the fibre) is carried out by adding the alkali (usually used soda ash).  Since the exhausted dye is already on the fibre, it is more likely that the exhausted dye reacts with the fibre in preference to water.

However the dye present in the dye bath (which contains a substantial amount of the reactive dye) can now react with water since it is under alkaline condition. It is already   stated that the hydrolyzed dye cannot further react with the fibre but dye to the affinity forces; it is absorbed by the fibre and is retained in it. During the subsequent washing or soaping the substantivity held hydrolyzed dye gets stripped into the washing bath thereby reducing the washing fastness of the dyeing. If the affinity of the original dye is reduced to a very low value, this problem will not arise and a rigorous treatment of the dyeing with boiling soap or detergent solution removes almost all hydrolyzed dye. However if the affinity is very low, exhaustion of the dye bath prior to fixation cannot be achieved substantially. This results in a larger amount of the reactive dye remaining in the dye bath and getting hydrolyzed when alkali is added subsequently.

If the dye has high affinity for cellulose like a direct dye, it becomes difficult to remove the hydrolyzed dye from the dyeing since it is also absorbed by and retained in the fibre by fairly strong affinity forces, through not as strong ass the covalent bond formed between the dye and the fibre. Hence in actual practice low affinity dyes are selected for converting in to reactive dyes.

Different methods of reactive dye application:

  1. Pad-batch method.
    1. Pad (alkali)-batch (cold) process.
    2. Pad (alkali)-batch (warm or hot) process.
  2. Pad dry method
  3. Pad steam method.

1. Pad-batch method:

a. Pad (alkali)-batch (cold) process:

Pad-batch cold method
Fig: Pad-batch (cold) method

Steps:

  1. The fabric is first padded in a padding mangle with reactive dye in presence of an alkali.
  2. The padded fabric is rolled in a batch and the batches are wrapped by polyethylene sheets and stored in wet condition for 1-24 hours at 200-300C in a room.
  3. During the storage period, the rolls may be kept slowly rotating to prevent seepage of the dye liquor.
  4. After storing time is finished fabric is washed in a rope washing machine to remove the unfixed dye from fabric surface.

b. Pad batch (hot) process:

Pad batch (hot) process
Fig: Pad batch (hot) process

Steps:

  1. The fabric is first padded in a padding mangle with reactive dye in presence of an alkali.
  2. The fabric is then passed in between infrared heater to preheat the padded fabric to 500C to 900C.
  3. The fabric is then batched on a large diameter roller in a hot chamber. The batching is done under controlled conditions of temperature and humidity for a sufficient time to ensure diffusion and fixation of the dye in the fibre. During this period the batch is kept slowly rotating to avoid the seepage of dye liquor.
  4. The cloth is then washed in a rope washing machine to remove the unfixed dyes.

2) Pad dry method:

Pad dry method
Fig: Pad dry method

Steps:

  1. Fabric is first padded in a padder with reactive dye in presence of an alkali.
  2. Padded fabric is then passed through a squeezing roller into a dryer. As a dryer cylinder, stenter etc may be used. During drying due to higher temperature fixation of dye in fibre increases and at the same time water is removed by evaporation.
  3. After drying fabric is washed in a washing machine to remove unfixed dye.

3) Pad steam method:

Pad steam method
Fig: Pad steam method

Steps:

  1. Fabric is first padded in a padder with the dye.
  2. It is then passed through between two squeezing roller in a dryer. Drying should be done slowly; otherwise precipitation of dye due to quick removal of water may take place leading to lower color value.
  3. After coming out from dryer fabric is padded in a padder containing salt and alkali. Due to salt exhaustion of dye takes place and due to alkali fixation occurs.
  4. Fabric then passed through a steamer where it is kept for 15-19 second. Due to high temperature here fixation rate increases.
  5. In this step fabric is washed in a washing machine to remove the unfixed dye.

Knit dyeing with reactive dyes (hot brand):

Recipe:

  • Anti creasing agent = 0.3g/L
  • Sequestering agent = 0.5 g/L
  • Glauber salt or NaCl = 80 g/L
  • Dye (reactive) = x%
  • Soda ash = 5g/L
  • Or caustic soda = 1 g/L
  • Acetic acid = 0.75 g/L
  • Soap = 0.25 g/L
  • M: L = 1:10
  • Time = 60 min
  • Temperature = 600-1000C

Function of these ingredients:

  1. Anti creasing agent is used to remove crease mark from fabric.
  2. Sequestering agent is used to convert hard water into soft water.
  3. Gluber salt is used for exhaustion of dye in the fibre.
  4. Soda ash and caustic soda are used for fixation of dye in the fibre.
  5. Acetic acid is used for neutralizing the dyed fabric.
  6. Soap is used for washing the dyed fibre.

Dyeing curve:

Dyeing curve of reactive dyeing

Procedure:
At first fabric, required water and required anti creasing agent is added in the dye bath. Then sequestering agent and gluber salt of required amount is added in the dye bath. Then the bath is kept rest for 5 minutes. After that reactive dye of required amount is added in the dye bath. After adding dye in the dye bath, the bath is kept for 30 minutes. During this period exhaustion of dye occurs in the fabric. Then required amount of alkali is added for fixation of dye into the fabric. After adding alkali we will wait for 50 minutes and then we will check the shade. If shade is all right then fabric will be taken for after treatment.

After treatment:

aftertreatment of reactive dye

  1. At first dyed fabric will be treated with hot water at 800C for 10 minutes.
  2. Then the fabric will be treated with stock solution of acetic acid for 10 minutes at 600C for neutralizing the fabric.
  3. Then the fabric is washing with soap solution for 15 minutes at 950C.

You may also like:

  1. Dyeing of Cotton Fabric with Reactive Dyes
  2. Printing of Cotton Fabric with Reactive Dyes
  3. Different Types of Reactive Dyes: Properties, Structures and Factors
  4. Different Types of Dyeing Process of Reactive Dye
  5. Dyeing of Cotton Fabric with Sulphur Dyes
  6. Printing of Polyester Fabric with Disperse Dyes
  7. Dyeing Process of Cotton Fabric with Azoic Dyes
  8. Chrome Dyes: Features and Chemical Classification
  9. Importance and Techniques of Dyes Selection in Textile Dyeing Process
  10. Salt Free Dyeing of Cotton Fabric with Reactive Dyes
  11. Different Types of Dyes with Chemical Structure
  12. Different Types of Dyestuffs in Relation to the Fiber Substrate

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3 thoughts on “Reactive Dyes: Classification, Dyeing Mechanism, Application & Stripping”

  1. Very good article.
    Please correct this sentence, OH is in the cellulosic polymer and Amino is in polyamide:

    Why reactive dye is so called?
    … This covalent bond is formed between the reactive group and terminal –OH (Hydroxyl) group of polyamide and wool fiber or between reactive group and terminal -NH2 (Amino) group of cellulosic fibre polymer. …

    Reply

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