What are direct dyes? Direct dyes are in the form of sodium salts of sulfonate or antelope, which ionize the dye anions and sodium ions in water. Direct dyes are used to dye flax under neutral or weak base conditions.
Under neutral or weak alkaline conditions, cellulose anions are formed in cellulose fibers, the surface of the fibers is negatively charged, and the sodium ions around the fibers are due to the coulomb gravity (that is, the gravitational interaction between two positive and negative charges. It is divided into gravitational force and repulsive force with the same number of charges as repulsive force), which must orient the fiber's interface transfer, and do the distribution of the diffusion layer on the surface of the fiber. The concentration is highest at the interface of the fiber. As the distance from the fiber interface increases, The concentration gradually decreases until it is comparable to the bulk concentration in the dye solution.
In order to maintain a neutral charge, an equal amount of dye anion must be transferred to the fiber interface in the dyeing solution. During the process of transferring the dye anion from the dye to the fiber interface, the coulomb force is a long-range force, and the dye pigment anion The first is the repulsion effect of negative ions on the surface of the fiber. Only those dye anions with higher energy momentarily due to the increase in temperature during collision or dyeing can overcome the diffusion energy resistance caused by this repulsion and break through certain obstacles. Within a certain distance range, the van der Waals force acting as a short-range force acts as the main force, thereby pulling the dye anion of the dye toward the surface of the fiber, being adsorbed by the surface of the fiber, and further spreading by the difference in the concentration of the inner and outer layers of the fiber. Enter the inside of the amorphous area of the fiber, complete the dye uptake process, and the dyeing process is basically completed.
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