Introduction:
The dyes are classified as water-soluble dyes and water insoluble dyes. Other types of classdification of dyes are synthetic dyes and natural dyes.The dyes available in the market,those are in the form of ready made, in the powder, some cases in paste form,used for dyeing of the fabrics or printing of the fabrics. Even dyes are used for paper printings.
Basic dyes:
Basic dyes are water insoluble dyes. These are not soluble in water directly when the powder form or paste form of the dye is dissolved in water, like reactive dyes, acid dyes, etc,.But the direct dyes are dissolved in water.Basic dyes are water insoluble,then how to make it dissolve in water ?.Without dissolution in water,the dye solution cannot be prepared.If the solution is not prepared,how the exhaustion takes place ?.That is the absorption of colour by fibers due to the affinity between the dye particle and the textile fibers.
So to prepare the dye solution, the basic dye must dissolve in water. It will require conversion of water insoluble dyes into soluble dyes. After dissolving only, it will be absorbed by the textile material.Textile material may be a yarn or fabric.
Protein fibers:
Basic dyes are used for dyeing of textile materials made from protein fibers. Acid dyes are also used to dye protein fibers. What are those protein fibers ?. Fibers, which are naturally available are silk and wool.
Silk is available in filament form. The substance present in the protein fiber silk is Fibroin.
Wool is made of the protein substance keratin extracted from skin of sheep.The fibers are naturally in the staple form.
And basic dyes are used to dye the synthetic fibers made from synthesized proteins. That is protein fiber made synthetically
These protein fibers, whichever fiber contain inside,the poly molecular structure, that is polymerization or polymerized structure.
Cellulosic fibers:
In previous days or even nowadays, the cellulosic fibers like natural cotton and regenerated viscose rayon are dyed by the basic dyes. But the fastness of a dye used for cellulosic fibers is very very poor, especially washing fastness.
Mordants:
The cellulosic fibers are dyed by basic dyes by the help of mordants.Mordants have affinity towards both dyes and textile fibers. Mordants are the chemical agents,also called as dyeing agents. Mordants will help to make the cellulosic material absorb the basic dyes. First the cellulosic material that may be yarn or fabric is mordanted. Mordanted means, the fabric or the yarn is treated with mordants. So that,it will make the cellulosic material to absorb the dye particles.Example of natural mordant is Tannic acid.
Mechanism of Dyeing:
What is the mechanism involved in the dying of cellulosic fibers and protien fiberd by the basic dyes ?. That is the basic dyes, when dissolved in water, even after treated with mordants,ionisation takes place in the dye bath.
The dye bath is neutralised with acetic acid or hydrochloric acid before the material is dipped for dyeing. If the dye bath is neutralised with hydrochloric acid, the chloride of the basic dyes are creates which are colourless in nature but negatively charged.Other coloured parts creates are the positively charged and are responsible for dyeing.These coloured part is called cation.
Cations are used to fix on the anion part or site of the macromolecules of the cellulosic fiber or protein fibers.The cation of the basic dye is a coloured part of the dye. And anion is a colourless part of the dye. For dyeing is required coloured part. That is cation is required.
If basic dyes are dyed with the cellulosic fibers, mordants are used.For protein fibers, no the mordant is required.
Whatever the free base dye having positively charged coloured part cation is making electrovalent bond with the anion part of the of the site of the macromolecules of the fiber. So that,the fixing of the color takes place.
Chemistry of Dyeing:
Basic Dyes have amino group in their molecular structure like -NH2, -N(CH3)2, -N(C2H2)2,etc,..are takes active part in the dyeing process.
Cellulosic fibers contain -OH (Hydroxy)groups in their molecular structure are takes active part in the dyeing process.
-COOH (Corboxy)group prefer in the polymer chains of protein fibers takes active part in the dyeing process.
After treatment:
Even after dying, the after treatments are required to improve the fastness of the day or to improve the shade of the dye.
Note: This article is going to be update time to time and as and when required.
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