Direct dye and its application:
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Dye that has a direct attraction to the fiber and can be applied directly, meaning that no other helper is needed here, is called direct dye. In other words, it is called direct dye as it is applied directly without using any other chemical. Direct dye is also called substantive dye. Because it has a strong addiction to cellulose.
Direct dye and its application-Description:
This class of dye is most attracted to cellulosic fibers. It is also called Substantive Dye and Direct Cotton Color. The first dye in this class, discovered by Boltiger in 1884, is called Congo red. Fibers other than synthetics are dyed directly by direct color.
Most direct dyes contain sulphonic acid or carboxylic acid-containing sodium (Na) salt and azo compound. As a result, they are easily soluble in water and create a colloidal solution. It is applied through alkali and it is cheap. This dye can be used for fibers other than hydrophobic fibers. Although animal fiber can be dyed by direct dye, it is not used without special needs. It is almost identical in structure to acid dye.
Direct dye and its application-Properties of direct dye:
The features of Direct Dye are as follows,
1) Direct dye contains a group of sodium salts of sulphonic or carboxylic acid, so it is soluble in water.
2) It is very easy to use and cheap.
3) It usually has a strong attraction to cellulose fibers, especially cotton and viscose rayon, but some direct dyes can also dye animal fibers.
4) Direct dye washing fastness is not good, but after treatment, its washing fastness, light fastness, etc. can be increased.
5) Different types of color shades can be done by the dye.
6) Abrasion and Perspiration in contrast to the durability of the dye is good.
6) Dye is not damaged by gas fading or hot pressing.
6) This dye can be applied through alkali and neutral.
Mechanism of direct dyes:
When cellulose fibers are immersed in a solution of direct dye, the dye molecules are rapidly absorbed by the cellulose micro molecules located on the fiber surface. The stages of dyeing theory that apply to direct dyeing on cotton are as follows:
1. The cellulose is driven into the direct dye dissolved bath and stirred with a stirring, causing the dyes to come closer to the fibers. In addition, the application of heat creates a kind of force of attraction. The dye comes close to the fiber surface from the dye bath.
2. As the dye molecule approaches the fiber surface, it is attracted by the fiber and forms a thin layer on the outer surface of the fiber. Thus the dye molecule is formed at that place near the fiber surface of the dye bath. As a result, the density of the space decreases. And to fill that low-density space, dye molecules start coming from higher densities. They are also attracted by the fiber to form a layer on the surface of the fiber and thus the process continues.
3. After the dye molecules form a layer on the surface of the fiber, it diffuses from the outer surface of the fiber to the inner surface. Dye diffusion depends on two factors. E.g.
a) Dye molecules and fibers on the surface.
b) On the gravitational force of dye and fiber.
4. A group of amino located in the dye that attaches to cellulose through a weak hydrogen bond.