What problems might arise during high-temperature dyeing?

Under high-temperature and high-pressure conditions, the average kinetic energy of polyester fiber macromolecular chains rapidly increases. Above 80°C, polyester fibers transition from a frozen state to a vitrified state. As the temperature continues to rise, the movement of the polyester fiber macromolecular chains instantly creates numerous voids within the fiber. Disperse dye molecules are simultaneously stimulated by heat and diffuse and sublimate within the fiber, accumulating a sufficient number of dye molecules to complete the dyeing process.

1)Problems with High-Temperature and High-Pressure Dyeing:

When dyeing polyester with disperse dye s, streaking can occur in polyester filaments. While streaking can be addressed by using disperse dyes with lower molecular weights, higher molecular weights are sometimes necessary due to their sublimation fastness. In these cases, a leveling agent is needed to eliminate streaking. When using disperse dyes with higher molecular weights for polyester, the dye only stains the surface of the fiber and does not penetrate the fiber core. Especially when dyeing with a mixture of disperse dyes with varying diffusion capacities, different colors will appear from the surface to the core of the polyester fiber. Therefore, an appropriate leveling agent is essential for dyeing. Due to the differences in polyester fiber structure and physical state, the instability of disperse dye dispersion, the complex interactions between various auxiliaries and dyes in the dyebath, and the temperature fluctuations during the dyeing process, a leveling agent is essential to overcome these unfavorable factors and achieve a leveling effect.

2)Mechanism of Action of High-Temperature Leveling Agents:

Leveling agents containing ethoxy groups work by a dye-affinity leveling effect, capturing disperse dyes during the dyeing process, increasing their availability and delaying dye uptake to achieve a leveling effect. If the leveling agent contains aromatic compounds, when the dyeing temperature reaches a certain critical value, it will cause the polyester fiber to rapidly plasticize and swell, and the glass transition temperature of the polyester will drop by 20-25°C. This significantly increases the voids within the fiber, promoting rapid and concentrated dye absorption. Furthermore, the leveling agent acts as a solvent for the dye, causing it to continuously desorb and migrate out of the fiber. This not only helps to improve the uneven dyeing caused by rapid dyeing, but also significantly reduces the dye uptake. If the leveling agent contains aliphatic compounds, it can both accelerate and slow dyeing under different dyeing temperature conditions, greatly improving the migration of disperse dyes, thereby achieving a uniform effect in high temperature and high pressure dyeing.

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