Views: 1 Author: Site Editor Publish Time: 2022-05-04 Origin: Site
Dyeing is the process of dyeing fibrous materials. It is by means of physical chemistry or chemical combination of dye and fiber, or by chemical method to generate dye on fiber and make the whole textile become colored objects. Dyeing products must not only have uniform color, but also have good color fastness.
According to the different dyeing objects, dyeing methods can be divided into fabric dyeing, yarn dyeing and loose fiber dyeing.Among them, fabric dyeing is the most widely used. Yarn dyeing is mostly used for colored fabrics and knitted fabrics, while bulk fiber dyeing is mainly used for the production of blended or thick dense fabrics, mainly woolen fabrics.
The purpose of dyeing research is to select and use dyestuff reasonably, make and process dyestuff correctly, and obtain high quality dyestuff.
The fiber is immersed in an aqueous solution of dye at a certain temperature, and the dye moves from the water to the fiber. At this time, the amount of dye in the water gradually decreases, and after a period of time, it reaches an equilibrium state.
The dye that's reduced in the water is the dye that's moving up the fiber. At any time to take out the fiber, even if twisted, the dye is still in the fiber, and can not simply make the dye completely separated from the fiber, this phenomenon of dye binding in the fiber is called dyeing.
If the sponge is immersed in the dye solution, the dye solution can also enter the inside of the sponge, but even if the time is long, the concentration of the dye solution does not change. When the sponge is taken out and twisted, the dye and water are extruded from the sponge at the same time, so the sponge is not dyed.
According to modern dyeing theory,The reason why dyes can dye fibers and have a certain fastness to fiber fabrics is that there are various gravitational forces between dye molecules and fiber molecules.The dyeing principle and dyeing process of various dyes are very different due to the characteristics of dyes and fibers.The dyeing process can be roughly divided into three basic stages.
1. The adsorption
When a fiber is put into a dyeing bath, the dye diffuses to the surface of the fiber and is gradually transferred from the solution to the surface of the fiber, a process called adsorption.Over time, the concentration of dye on the fiber gradually increases, while the concentration of dye in the solution gradually decreases, and after a period of time, the state of equilibrium is reached.The reverse process of adsorption is desorption. Adsorption and desorption exist simultaneously in the dyeing process.
The dyes adsorbed to the surface of the fiber spread into the fiber until the concentration of the dye in each part of the fiber becomes uniform.Because the concentration of dye adsorbed on the surface of the fiber is greater than that inside the fiber, the dye diffused from the fiber surface to the fiber interior.At this point, the diffusion of dye breaks the initial adsorption equilibrium, the dye in the solution will continue to adsorb to the surface of the fiber, adsorption and desorption again to balance.
It is the process of the combination of dyes and fibers, with different dyes and fibers, its combination is also different.
The three stages mentioned above often exist at the same time in the dyeing process and cannot be separated completely. It's just that at some point in the staining process one process dominates.
The fixation of the dye in the fiber can be considered as the process by which the dye remains on the fiber.Different dyes and different fibers have different principles of fixation. Generally speaking, there are two types of dyes that are fixed on fibers.
1. Pure chemical fixation
It refers to a chemical reaction between a dye and a fiber that causes the dye to stick to the fiber.
For example, reactive dyes dye cellulose fibers and form ether bonds with each other.
The general formula is as follows:
DRX+Cell-OH → DR-0-Cell+HX
DRX：Reactive Dye Molecule X:Active Group Cell-oh: cellulose
2. Physical and chemical fixation:
Due to the mutual attraction between the dye and the fiber and the formation of hydrogen bond, the dye is fixed to the fiber. Many cotton dyes, such as direct dyes, sulfide dyes, VAT dyes, etc., are dependent on this gravity and fixed on the fiber.