Polyester is a hydrophobic fiber. The fiber lacks groups that can bind to dyes. It cannot be dyed with water-soluble dyes. It can only be dyed with non-ionic disperse dyes with low molecular weight, no strong ionic water-soluble groups, and low solubility. Polyester has a compact structure and is dyed under normal pressure. It is difficult for the dye to diffuse into the fiber and dye the fiber through.
Above the glass transition temperature, the fiber macromolecular segments move violently, the gap between the polymer molecules increases, the free volume increases, and the dyeing rate increases, and the dye diffuses according to the free volume model.
It can be achieved by increasing the dyeing temperature (high temperature and high pressure dyeing method, hot melt dyeing method) or using fiber bulking agent and dyeing accelerator (carrier dyeing method).
Hydrogen bond——The ester group content in polyester is about 46%. Disperse dyes contain -OH and -NH2. In addition, the benzene ring of polyester can also form hydrogen bonds.
Van der Waals forces.
Hydrophobic bond-the interaction between the fiber and the dye through the hydrophobic part.
According to the principle of similar compatibility, the dye can be regarded as "dissolved" in the amorphous area on the solid fiber.
Increase, A. The movement of fiber macromolecules intensifies, the macromolecular chain rotates violently, the free volume of the fiber increases, the resistance of the diffusion space decreases, and the diffusion rate increases; B. The dye diffusion kinetic energy increases, which is beneficial for more dyes to diffuse into the fiber ; C. Increase the solubility of dyes and increase the dyeing rate.
The dyeing temperature was increased from 85 ℃ to 100 ℃, and the diffusion rate increased nearly 48 times.
The bulking agent is conducive to fiber expansion, reduces the glass transition temperature of the fiber, increases the free volume of the fiber, and improves the diffusion of the dye into the fiber. The accelerator promotes the surface adsorption of the dye fiber, increases the dye concentration on the surface of the fiber, increases the difference between internal and external concentration, and increases the dyeing rate. Some carriers have the dual functions of fiber bulking agent and dyeing accelerator. A proper amount of penetrant can shorten the dyeing time and get a good dyeing effect.
Improved solubility is conducive to the adsorption and diffusion of monomolecular dyes, and increases the dyeing rate.
However, the solubility of the dye should not be too high, otherwise the hydrophilic ability of the dye is greater than that of the fiber, and the equilibrium dyeing percentage will decrease.