In high-temperature and high-pressure dyeing, the dyeing process of disperse dyes on polyester fiber can be divided into the following stages:
(1) with the flow of dye in the dye solution, disperse dyes gradually approach the fiber interface. At this stage, the properties and state of disperse dyes are basically irrelevant. The dissolved dye molecules and suspended dye particles flow with the dye solution, and the transfer rate is determined by the flow rate of the solution.
(2) since there is a kinetic boundary layer on the surface of the fiber that is not easy to flow, when the disperse dye enters the kinetic boundary layer and is close to the fiber interface, it mainly approaches the fiber by its own diffusion. In this stage, the transfer speed is not only related to the solution velocity, but also to the diffusion speed of disperse dyes. Therefore, the diffusion speed of dissolved dye molecules is much faster than that of suspensions and aggregates. The solubility and dispersion state of disperse dyes have a great influence on the transfer speed at this stage.
(3) when the molecular force between disperse dyes and fibers near the interface is large enough, disperse dyes are quickly absorbed by the fiber surface. The transfer rate at this stage is mainly determined by the structure and properties of the fiber and dye molecules, as well as the properties of the interface solution. Among them, the solubility and dispersion state of dyes have great influence, the higher the solubility of dyes and the higher the effect of dye molecules and fibers, the faster the adsorption speed.
(4) after the disperse dye is adsorbed on the fiber surface, a concentration difference or internal and external dye chemical potential difference will be generated in the fiber, and the dye will diffuse to the internal fiber, where the diffusion speed is mainly determined by the fiber chemistry and microstructure, as well as the dye molecular structure and concentration. The content of the amorphous zone of the fiber is high, the pore size is large or the free volume content is large, the dye solubility is high, and the diffusion speed is fast. Therefore, the diffusion speed of the dye in this stage is directly related to the degree of swelling or plasticization of the fiber and the concentration of disperse dye in the fiber. High degree of swelling or plasticization, fiber layer disperse dye concentration, diffusion is fast. It can be seen from the above that the dyeing speed depends not only on the structure of dye and fiber, but also on the solubility of dye in solution and the swelling or plasticizing degree of fiber during dyeing.
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