Dyeing theory of direct dyes

Dyeing theory of direct dyes:

The following factor increases substantivity growth in direct dye.

1) Linear molecule

2) Trans isomer

3) Benzene nuclei must be coplanar

4) Conjugated double bond

5) Hydrogen bond formation

6) Vander Waals force

1. Linear molecule:

Most dye halls are dye AZO compounds. Meyer was the first to describe the increased linear molecular structure of the dye, with substantivity attached to it in such a way that it could be arranged on the surface of the fiber itself. It can easily penetrate the fiber, as the dye has a greater ability to attract fiber. https://bdfabric.com/factors-affecting-the-absorption-of-direct-dye/

2. Dyeing theory of direct dyes-Trans Isomer:

AZ0 and other groups form prominent molecules of CIS isomer. When this concept is applied to AZO dye molecules, it can be observed that trans isomers can become linear molecules but not CIS. It can be seen that not only the Trans isomer is substantive. but also a commercial dye, and it is assumed that the CIS isomers are transformed into Trans configuration, which is subsequently absorbed by the fiber. https://bdfabric.com/what-is-the-dyeing-process-in-textile/

3. Dyeing theory of direct dyes-Benzene nuclei must be complanar:

Hodgson discovers information about the relationship between structure and substantivity. For its substantivity, not only should the molecule be linear, but the Benzen nuclear must be coplanar.

These benzene nuclei can rotate independently so they are not coplanar and are non-substantive. That is why it is substantive. Thus, if the benzene nucleus of the dye is coplanar, the addiction to fiber is greater.

4. Conjugated Double Bond:

If there is a conjugated double bond in the dyestuff, the affinity towards cellulose will be more.

– C = C – C = C- (conjugated double bond).

According to Lead, the affinity is due to the interaction between the electrons in the extended conjugated system.

5. Hydrogen bond:

R-NH2 + HO – cellulose

R-N-H …. 0 – cellulose

Cellulose has a hydroxyl group, so it can form an H-bond with the -OH, -NH2, and -N = N– groups contained in dyestuff. This increases the affinity of the dyestuff to the fiber and the dye is substantive. So dyestuff, if you can form H-bond, it is substantive.

6. Vander Waal’s force:

R- SO3 Na → R SO3 (+ -) / Na (+)

Cell – OH → OH (-) + cell

Two negative charges for Vander Waals force attract each other. As a result, Dyestuff is attracted to fiber. This is why dyestuff is substantive.