What is competitive dyeing
The process in which the dye in the dye bath transfers to the fiber and enters the inside of the fiber. Dyeing is usually carried out in a dye aqueous solution at a certain temperature.
The process is roughly:
The dye arrives with the flow of the dye bath around the fiber;
The dye relies on its own thermal motion to diffuse and approaches the fiber surface through the liquid layer around the fiber;
Dye is caused by intermolecular Various forces are absorbed by the fiber, and the concentration of the dye bath around the fiber decreases;
The dye diffuses into the fiber in the amorphous region of the fiber and is adsorbed.
During the dyeing process, generally dyes and fibers do not undergo covalent bonding. The stain is reversible. At a certain temperature, the dyeing rate is high in the initial stage. As time increases, the dye concentration on the fiber gradually increases, the dye concentration in the dye bath decreases accordingly, and the dyeing rate also gradually slows down; finally, the dyeing percentage no longer changes with time. And change, reaching a state of equilibrium. The dye uptake percentage at this time is called the equilibrium dye uptake percentage.
Due to the reversibility of dyeing, during dip dyeing, the dye dyed on one part of the textile will be transferred to another part through desorption, diffusion and the flow of the dye liquor, causing the textile to become stained. Dyeing is even, this phenomenon is called dye transfer.
When dyeing reaches equilibrium, the relationship between the dye activity ɑf on the fiber and the dye activity ɑs in the dye bath can be measured by the thermodynamic function standard dyeing affinity (referred to as dyeing affinity)-△μ°:
Where R is the gas constant, T is the thermodynamic temperature, and the activity is a function of concentration. Dyeing is an exothermic process. Increasing the dyeing temperature will decrease the equilibrium dyeing percentage and the dyeing affinity.
After adsorption under constant temperature conditions, after dyeing reaches equilibrium, the relationship between the dye concentration on the fiber and the dye concentration in the dye bath can be expressed by the adsorption isotherm.
The adsorption isotherm of hydrophobic fibers such as acetate dyed with disperse dyes is basically a straight line. The amount of dye dyed increases as the concentration of the dye bath increases until both the fiber and the dye liquor reach saturation.
Wool and nylon are dyed with leveling acid dyes, and the slope of the adsorption isotherm gradually decreases as the concentration of the dye bath increases. Finally, the dyed dye no longer changes with the concentration of the dye bath and reaches the dyeing saturation value of the fiber. Its size is related to the amino content of the fiber.
Polyamide 66 has a low amino content, so it is difficult to dye strong colors with leveling acid dyes under normal conditions. When dyeing in color combinations, competition between two dyes will occur if the concentration is too high. The adsorption isotherm of acrylic fiber dyed with cationic dyes also belongs to this type.
Nouns related to dyeing
1. Initial dyeing rate: the percentage (or dyeing rate) in the early stage of dyeing
2. Level dyeing: the degree to which the dye is evenly distributed on the surface of the dyed object and inside the fiber. Whether the various parts of the surface of the dyed object are evenly distributed, and whether the dye is evenly distributed within the fiber. Examples of four situations of distribution within fibers.
3. Dye migration: The dye from the more dyed parts is transferred to the less dyed parts through desorption.
4. Interface dyeing and whole-process dyeing: The so-called interfacial dyeing means that the dye is adsorbed from the solution to the surface of the fiber, and is desorbed into the dyeing solution before it diffuses into the interior of the fiber, and then from the dyeing solution. Re-adsorb to areas with less dye.
The so-called dye migration in the whole process means that the dye that has diffused inside the fiber diffuses from the inside to the outside, diffuses to the surface of the fiber, and then desorbs into the dye liquor, and is re-adsorbed from the dye liquor to the fiber surface. Parts that are less stained. In the early stage of dyeing, the dye migration mainly occurs at the interface, and in the late stage of dyeing, the whole process of dye migration mainly occurs. </p
