When polyester dyeing auxiliaries are dyed at high temperature and high pressure, the dyeing process of disperse dyes on polyester fibers can be divided into the following stages:
(1) Disperse dyes move closer to the fiber interface with the flow of dye solution. At this stage, the properties and state of disperse dyes are basically independent. Both soluble dye molecules and suspended dye particles flow with dye solution, and the transfer rate depends on the flow rate of solution solution.
(2) Because there is a dynamic boundary layer on the surface of the fibers which is not easy to flow, when the disperse dyes enter the dynamic boundary layer near the interface of the fibers, they approach the fibers mainly by their own diffusion. In this stage, the transfer rate is not only related to the flow rate of the solution, but also to the diffusion rate of disperse dyes. Therefore, the disperse dye molecules diffuse much faster than suspensions and aggregates. The solubility and disperse state of disperse dyes have a great influence on the transfer rate at this stage.
(3) When the molecular interaction between disperse dyes and fibers is large enough, the disperse dyes are adsorbed rapidly on the surface of fibers. The transfer rate at this stage is mainly determined by the structure and properties of the fibers and dye molecules, and also by the properties of the interfacial solution. Among them, the solubility and dispersion of dyes have great influence. The higher the solubility of dyes and the greater the interaction between dye molecules and fibers, the faster the adsorption rate is.
(4) When disperse dyes are adsorbed on the surface of fibers, a concentration difference or chemical potential difference between internal and external dyes will occur in the fibers, and the dyes will diffuse into the fibers, where the diffusion rate is mainly determined by the fibrology and micro-structure, as well as the molecular structure and concentration of dyes. The content of amorphous zone 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 dye diffusion speed at this stage is directly related to the degree of swelling or plasticization of the fiber and the concentration of disperse dyes in the fiber. High swelling or plasticizing degree, high concentration of disperse dyes in the outer layer of the fiber, rapid diffusion. It can be seen from the above that the dyeing speed depends not only on the structure of dyes and fibers, but also on the solubility of dyes in solution and the swelling or plasticizing degree of fibers during dyeing.
