Introduction of Reactive Dye | History of Rective Dye | Uses ofReactive Dye

Dye that reacts with the textile fiber to produce both a hydroxyl and an oxygen linkage, the chlorine combining with the hydroxyl to form a strong ether linkage; gives fast, brilliant colors.

History of Reactive Dyes
Reactive dyes first appeared commercially in 1956, after their invention in 1954 by Rattee and Stephens at the Imperial Chemical Industries Dyestuffs Division site in Blackley, Manchester, United Kingdom.

Reactive dyeing is now the most important method for the coloration of cellulosic fibres. Reactive dyes can also be applied on wool and nylon; in the latter case they are applied under weakly acidic conditions. Reactive dyes have a low utilization degree compared to other types of dyestuff, since the functional group also bonds to water, creating hydrolysis of Reactive Dye.

Reactive dyes have good fastness properties owing to the bonding that occurs during dyeing. Cotton is made of cellulose molecules which react with the dye .During reactive dyeing the H atom in the cellolose molecule combines with the cl atom in the dyeing process and results in a bond. Trifunctional dyestuffs also exist.

Uses of Reactive Dye

Reactive dyes are used to dye cellulosic fibres. The dyes contain a reactive group, either a haloheterocycle or an activated double bond, that, when applied to a fibre in an alkaline dye bath, forms a chemical bond with an hydroxyl group on the cellulosic fibre.

Supercritical Fluid (SCF) | Supercritical Fluid Dyeing | Advantages ofSupercritical Fluid Dyeing

Supercritical Fluid (SCF)

Supercritical fluid is one kind of fluid which is highly compressed gases which combine properties of gases and liquids in an intriguing manner.It is a substance which can be either liquid or gas, used in a state above the critical temperature and critical pressure where gases and liquids can coexist. It shows unique properties that are different from those of either gases or liquids under standard conditions.A supercritical fluid has both the gaseous property of being able to penetrate anything, and the liquid property of being able to dissolve materials into their components.

Supercritical Fluid Dyeing
In textile industry water is the usual medium for dyeing and cleaning. This is the reason why textile industry is one of the biggest consumer of water in all industries. Textile refining processes without using water have to be applied because costs of water and waste water are increasing more and more, the legislator fixes more rigorous limit values for the sewage load and also the water resources become more and more limited in several areas.

Supercritical Fluid graph

In cooperation with the DTNW (German textile research centre Northwest) Uhde has developed a textiles-refining process which is uncoupled completely from the water cycle. Therefore the new, ecologically sensible ways which are enough, moreover, also for the highest quality requirements are opened to the dyeing by textiles.

Advantages of Supercritical Fluid Dyeing
This relatively new and innovative process offers unbeatable advantages compared to conventional dyeing.

1. Qualitatively equivalent, partially better dyeing result
2. No damage of the fibre
3. Significantly shortened process and dyeing times
4. Low dye and chemicals consumption
5. No water consumption
6. No reductive post laundry necessary
7. CO2 is easily recyclable
8. No drying process and therefore no drying devices necessary
9. CO2 is innocuous and ecologically friendly
10. Energy savings - by the short process times, the lower heat capacity of the CO2 compared with water and no need for drying of the material after the dyeing.

The Dyeing Process
The textiles to be dyed are wrapped on a dyeing beam to achieve an equal dyeing result. The dyeing beam is placed in the dyeing autoclave C and the dyestuff is filled into the receiver D2. The pressure vessels are closed and is CO2led in several steps through the plant.

1. Pretreatment
In the first step the textiles are cleaned from pollutions and sticking auxiliary materials from the production because the rests of wax, oils and other hydrophobic substances can disturb the dyeing process. With the pressurization pump P1 liquid CO2 from the buffer tank D1 is compressed to supercritical pressure and heated up in the heat exchanger E1 to supercritical temperature. The supercritical CO2 flows through the textiles in the dyeing autoclave C and, besides, solves carefully all sticking pollutions from the fibres. The loaded CO2 flows via a expansion valve and becomes by the pressure decrease gaseous. Thereby the solution power is reduced and the extracted pollutions precipitate and are collected in the separator S. Afterwards the cleaned CO2 is liquefied in the condenser E3 and is led via the buffer vessel D1 back into the circulation.

2. Dyeing
After the pre-treatment the actual dyeing process begins by switching of the dyestuff receiver D2 into the CO2circulation. The supercritical CO2 solves the dyestuff in the dyestuff receiver and flows through the dyeing autoclave C. The CO2 loaded with dyestuff is delivered through the textiles and the dyestuff is adsorbed in the fibres. After the dyeing autoclave the CO2 flows through a filter to the circulating pump P2 and afterwards is fortified in the dyestuff receiver with fresh dyestuff and is led as long as in the circulation, until the desired dyeing intensity of the textiles is achieved.

3. After Treatment
After finishing the dyeing step the CO2 circuit and dyed Material are cleaned from excess dyestuff. Therefore the dyestuff receiver is taken out of the CO2 circuit and the loaded CO2 is expanded via the expansion valve into the separator. The excess dyestuff precipitates fall out and is collected in the separator. The CO2 is circulated as long as the plant and the textiles is cleaned from the excess dyestuff leftovers.

After finishing the complete dyeing process the CO2 circulation is stopped and the dyeing autoclave is depressurized to atmospheric conditions. The dyed textiles are taken out of the autoclave.

Dyeing of Cellulosic Fibres with Sulpher Dyes | Sulpher Dyeing Processof Natural Fibers

The sequence of dyeing with Sulpher dyes is as following:

Goods Preparation
↓
Dye Solution preparation
↓
Dyeing
↓
Oxidation
↓
After treatment
↓
Dyed Goods

Ø Typical Recipe:
The Typical recipe for dyeing is as below:-

1. Sulpher Dye  : 10% (On the weight of the fabric)
2. Na2S (Reducing Agent)  : 1.5%(on the weight of the Dye)
3. Salt  : 8 gm/litre(NaCl)
4. Soda Ash (NaCO3)  : 7 gm/litre
5. Temperature  : 1000C
6. Time  : 90 minutes
7. Material: Liquor  : 1:20

Sometimes a chelating agent EDTA is added to chelate any metal salt extracted from the cotton goods & effectively remove these ions from the dye bath. This is necessary to prevent a harsh texture forming on a textile.

Ø Good Preparation:
Only normal pretreated fabric (scoured, bleached) is required. Mercerized cotton goods causes an increased colour yield of 30-40%, But goods bleached by Na-Hypochlorite should not be dyed by Sulpher dyes:

Ø Dye solution preparation or Reducing Step:
Required amount of dye, soda ash & Na2S are taken in a beaker and a little amount of cold water is added to make a paste. In a separate vessel the rest of the water is boiled and the paste is added to it. Then the mixture is boiled for 5 minutes to make the dye completely reduced.

Ø Dyeing:
At first dye solution is taken in a dye bath & the fabric is immersed in that solution. Then it is heated for 10-15 minutes. Then half of the total NaCl solution is added and temperature is raised to boil & then the rest amount of NaCl is added. Dyeing at this temperature is continued for about 30 minutes. Then the steaming is turned off and the application continued in cooling liquor for a further half hour. This steaming helps to diffuse the dye in to the fabric before fixing. Retained dye liquor should be rinsed out immediately from the surface of the fabric.

Dyeing Curve

Ø Oxidation:
After dyeing the reduced water soluble form of the dye should be make insoluble by oxidation, to fix it on the fabric permanently. For this oxidation, we may use K2Cr2O7, CH3COOH. Na-perborate, Na2O2 etc. The typical recipe of oxidation is as below:

1. Na-Perborate à 0.5-1 gm/litre
2. Temperature à 40-500C
3. Time à 20 minutes.

Ø After Treatment:
1. The dyed substance is soaped which makes the colour bright and makes shade permanent.
2. The light fastness property of Sulpher dyes which is generally good can be improved by after treatment with certain metallic salts. Thus a treatment with CuSO4 & CH3COOH in presence of K2Cr2O7 improves the light fastness. When the dichromate is also present the washing fastness is slightly improved.

The following recipe is used for after treatment:

CuSO4 Solution à 1-2% (on the weight of goods)
CH3COOH (60%) à 1-2%
Temperature à 700C
Time à 20-30 Minutes
 

Precaution in the dyeing process: 

 
The precautions in the dyeing process with the Sulpher dyes are mentioned below:-
1. In the application of Sulpher dye, the dye bath should not contain Ca- Salts. If they are present in the form of insoluble co-compounds with the Sulpher dyes which precipitated easily in closed machines and form sludge when restrict the circulation of the dye liquor.
2. The dye should be dissolved with soda.
3. Great care should be taken during reduction process because over reduction should lower the affinity of dye towards the fibre. As a result dull shade will appear and a lot of dye stuff will go to waste.
4. Fabric must not to expose to air during dyeing to prevent precipitation & oxidation. This will cause uneven dyeing.
5. To prevent uneven dyeing in the fabric selvedge more amount of Na2S or NaOH and salt should be added in case of the jigger dyeing machine.
6. To prevent the broziness the dye liquor should not be very worm.
7. Goods dyed with Sulpher black should be after treated with a solution of K2Cr2O7 followed by rinsing. This will prevent Sulpher black tendering.
 

Control of Dyeing:
Reduced Sulpher dyes are similar to direct dyes. Because they can also be exhausted by adding common salts (NaCl) or Glauber’s salt (Na2SO4.10H2O) to the dye bath.

Sodium bi sulphite (NaHSO3) and ammonium sulphate {(NH4)2SO4} may also act as exhausting agents. Especially in dyeing combination shades. NaHSO3 is an acidic salt and (NH4)2SO4 is an acid liberating agent. They reduce the pH of dye bath and produce 15-20% deeper shades than common salt, when used as the exhausting agent. But the shades produced in presence of them are less bloomy and dull.

When NaHSO3 is used alone the rate of exhaustion is low but the produced shade is brighter and bloomier than common salt (NaCl) dyeing.

The use of the exhausting agents causes wastage of dye but as the Sulpher dyes are relatively cheap this wastage is not considered. Especially in case of medium & light shades. 


Improving of Fastness Properties:

The light fastness of the Sulpher dyes which is generally good can be improved by after treatment with certain metallic salts. Thus a treatment with CuSO4 & CH3COOH in presence of K2Cr2O7 or Na2Cr2O7 improves the light fastness. When the dichromate is also present the washing fastness is slightly improved. In actual practice the following after treatments are given: -

1. CuSO4 Solution à 1-2% (on the weight of goods)
2. CH3COOH (60%) à 1-2%
3. Temperature à 700C
4. Time à 20-30 Minutes

The latter one also improves the washing fastness of Sulpher dyed textile materials.

Knit Dyeing with Reactive Dyes(Hot Brand) | Knit Dyeing with Hot BrandReactive Dyes

Knit dyeing with reactive dyes :

Recipe:

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

Function of these Ingredients:

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

Dyeing Curve:

Dyeing Curve

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 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 600Cfor neutralizing the fabric.
3) Then the fabric is washing with soap solution for 15 minutes at 950C.

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: - 

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.