Basic dyeing process:
According to the viewpoint of modern dyeing theory, the reason why dyes can dye fibers and have certain fastness on fiber fabrics is because of the various attractive forces between dye molecules and fiber molecules. The dyeing process varies greatly due to the characteristics of dyes and fibers, and cannot be generalized.
As far as its dyeing process is concerned, it can be roughly divided into three basic stages.
When the fiber is put into the dye bath, the dye first diffuses to the surface of the fiber, and then gradually transfers from the solution to the surface of the fiber. This process is called adsorption. With the passage of time, the dye concentration on the fiber gradually increased, while the dye concentration in the solution gradually decreased, and after a period of time, an equilibrium state was reached. The reverse process of adsorption is desorption, and adsorption and desorption exist simultaneously in the dyeing process.
The dye adsorbed on the fiber surface diffuses into the fiber until the dye concentration of each part of the fiber tends to be the same. Since the dye concentration adsorbed on the fiber surface is greater than the dye concentration inside the fiber, the dye is promoted to diffuse from the fiber surface to the fiber interior. At this time, the diffusion of dyes destroys the initially established adsorption equilibrium, and the dyes in the solution are continuously adsorbed to the fiber surface again, and the adsorption and desorption reach equilibrium again.
It is the process of combining dyes and fibers. The combination of dyes and fibers is different.
The above three stages often coexist in the dyeing process and cannot be completely separated. It is just that a certain process prevails during a certain period of dyeing.
How the dye is fixed in the fiber:
The fixation of the dye in the fiber can be regarded as the process of the dye being retained on the fiber. Different dyes and different fibers have different fixing principles between them. Generally speaking, there are two types of dyes that are fixed on fibers.
1. Pure chemical fixation
Refers to the chemical reaction between the dye and the fiber, so that the dye is fixed on the fiber.
For example: reactive dyes dye cellulose fibers, which form ether bonds with each other.
The general formula is as follows:
DRX : reactive dye molecule
X : active group
Cell-OH: stands for cellulose
15. Physical and chemical fixation
Due to the mutual attraction between the dye and the fiber and the formation of hydrogen bonds, the dye is fixed on the fiber. Many cotton dyes, such as direct dyes, sulfur dyes, vat dyes, etc., rely on this attraction to be fixed on the fiber.