Relationship between the molecular structure of dyestuffs and the fastness of wet treatment
Time:
2023-11-21
Dyestuffs must have a certain degree of wet processing fastness, including resistance to washing, soaping, wet rubbing, alkaline boiling and shrinkage fastness. Wet processing fastness is directly related to the diffusion properties of the dye molecules in the fiber, the relative molecular mass of the dye, the molecular configuration and the binding force between the dye and the fiber.
The molecular structure of the dyestuff determines the size of the binding force on the dyed fiber, the larger the binding force, the weaker the hydrophilicity, the dyestuff molecules dyed inside the fiber are retained in the fiber and are not easy to diffuse outwardly, the higher the fastness to wet treatment. The rate of desorption of certain acid dyes from wool fibers into alkaline buffer solutions decreases as the "dye-fiber" bonding force increases, and the rate of desorption of dyes decreases as the alkalinity of the solution decreases.
There are different ways to increase the relative molecular mass of dyes. Early azo dyes synthesized with benzidine as the diazo component, including some acid dyes, have a better molecular coplanarity, which improves the fastness to wet treatment of acid dyes more than the relative molecular mass factor. This planar structure provides more opportunities for van der Waals and hydrogen bonding between the dye molecules and the fibers.
A more practical way to increase the relative molecular mass is to introduce hydrophobic groups such as aliphatic alkyls, cycloalkanes and aromatics into the dye molecule. The introduction of these groups not only reduces the solubility and hydrophilicity of acid dyes in water, but also increases the gravitational force between the dye molecule and the protein fiber molecule, which significantly improves the fastness to wet treatment of dyes. For example, the acid dyes synthesized by using p-alkylaniline with different carbon chains as diazo component and H acid acylation product, when the carbon chain length and relative molecular mass increased, the fastness to soaping also increased.
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