Reactive dye is the most important dye class for cellulosic materials. In the mid-1980s worldwide consumption of reactive dye for cellulosic material was 10-12% whereas about 40% of total dye consumption was presented by Japan alone. It offers a wide range of dyes with varying shades, fastness with high brilliancy and reproducibility.
Nowadays in our country reactive dye is extensively used to dye cellulosic materials. Honestly, when you will visit most of the dyeing factory, you will find only reactive dyes there for cellulose dyeing purpose.
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Reactive Dye Definition
Reactive dye is a dye class having reactive group in it and it works like magic. It creates covalent bond with the fiber and becomes an integral part of the fiber structure.
Good fastness properties, dye reproducibility, lower price, ease of dyeing method – all these features increase the popularity of dye day by day. Procion, Cibacron (Ciba), Remazol (Dystar) etc are the most common dyes used by the factory.
Interested to know more about Reactive Dye Trade Names click here
History of Reactive Dye
In 1955, two chemists named Rattee and Stephen who are working for ICI in England tried to invent a noble process for cotton dyeing. They used water soluble dyes that contains dichlorotriazine groups. They applied the dye to the cellulose from a neutral bath and then increasing the pH value.
They found that under mild alkaline condition a reactive chlorine atom on the triazine ring being substituted by an oxygen atom from hydroxyl group of cellulose.
They succeeded and developed a new dye named REACTIVE DYE. An example of such dye is C.I. Reactive Orange 1. Reactive dyes are now widely used for dyeing cellulosic fabrics. But protein fibers can also be dyed with reactive dyes.
Reactive dye components
Consider a general structure –
Where, D = Dye chromophore (Azo, Anthaquinone, Metal complex, Phthalocyanine group)
S = Solubilising group (-SO3Na)
R = Reactive group (-Cl, -Br, -SH, -OCH)
B = Bridging group (Amino, Oxide, Sulphur, Ethyl, Methyl group)
Temperature: Depends on the brand of dye
pH: strong alkaline pH 10.5-11
Time: 60 to 90 min
Liquor ratio: Higher liquor ratio is better
Concentration of electrolyte: Determines the depth of shade
If you want to know details about these factors then click here:
Reactive Dye Reaction
Typical reaction with cellulose:
Here, Cell-OH is cellulose which has reactive hydroxyl group
Dye-Cl is the dye which has reactive chlorine group
Cell-O-Dye is dyed cellulose where dye is linked to the cellulose by covalent bond
Reactive dyes comprise a chromophore and a reactive group. In this way, they differ from other dyestuffs.
They chemically react with the textile fibers by forming covalent bond. They create covalent bond with the terminal reactive hydroxyl group (-OH) of cellulose and -NH2 group of protien fibers.
The formation of covalent bond is a chemical process which is stronger than other bonds like Van der waals forces, hydrophobic bond, hydrogen bond or coulombic attraction of ions.
Chemically cellulose behaves like polyhydric alchohol. Reactive dyes only react with cellulose under alkaline condition.
For this reason this dyes are called reactive dyes.
Reactive Dye Hydrolysis
Reactive dye is hydrolyzed and this is the most important drawbacks of it. You can’t keep your dye solution for long time once it is prepared. The reason is the high percentage of dye hydrolysis. About 20-40% reactive dye is hydrolyzed.
The reactive group of reactive dye reacts with the water instead of cellulose. It is called hydrolysis.
Mechanism of Reactive Dye
3 steps of dyeing mechanism of reactive dye.
In exhaustion stage, dyeing starts from neutral bath. For substantivity some dyes are taken up by the fiber. In this stage, salt is added to promote dye uptake. Temperature also gradually increase.
In fixation stage, alkali is added to increase the pH of the bath and this stage helps to fix the nucleophilic cellulosate ions with dyes.
The rinsing process washes off and removes all the unfixed dye particles.
How to use reactive dye?
Wanna dye your favorite dress at home? Not to worry. Reactive dye would be a better solution.
Fiber Reactive Tie Dye
Tie dye is as simple as its name implies. You can easily do it at home. Color your favorite textiles with the simple ways.
The technique described below pretty much consists in preparing a dye bath in which the fabric is to be fully submerged.
Preparing dye bath
Firstly, start by picking up your color.
Your supplier will tell you about the amount you need to be used. But it is a wiser way to start with little and then take a look of it and if you think that you need a stronger color, then add more color to it.
Using a whisker mix the color well in water.
Preparing the dye activator
For the activator use washing soda or soda ash. For fixation of reactive dye we need alkali. So, here soda ash or washing soda should use for efficient dyeing.
For a pound of fabric, use a gallon of water with five teaspoons of washing soda.
Washing soda really likes to dissolve in hot water. So make sure your water is hot and pre-dissolve the washing soda into it so that you can use this later with dye solution.
Use a whisker to completely dissolve the soda in water.
At the very beginning, it may look cloudy but will become transparent soon as it dissolved completely.
Preparing Fabric for dyeing
Soak the fabric in water once you tied and bundled it in your tied pattern. You can use rubber band for making knot.
Before trying any dyeing technique, just wet the fabric well. Because it helps to penetrate the dye molecules inside the fabric.
And yeah, this helps to get you the better result.
Add all the ingredients in a single bath. Firstly the dye solution followed by the dye activator.
Make sure to keep stirring by whisker to mix all of them very well.
Now put the wet fabric and make sure it is submerged well.
Use any spatula or use the whisker or your hand to keep the fabric underneath the water as it tends to float.
Now you are done with it. Wait for an hour. In this time, dye-fiber reaction will take place.
After an hour, remove the fabric from the bath and squeeze it and rinse well.
After that dry and iron the fabric.
Now it is perfectly ready to wear.
Last Though on Reactive Dye
Reactive dye is a popular dye in the dyeing industry. Most of the cases the cellulose materials are dyed with reactive dye. The color brilliancy and easy usage along with the low price has made this dye so popular.
Salma Hasin Shila, the author of this site completed her BSc. in Textile Engineering (Wet Processing Engineering) from www.butex.edu.bd (BUTEX). She has a passion for textile technology and loves to write about it. She wants to share her knowledge to help the students in their studies and businessman & entrepreneurs in their business in making wise decisions fast.