Cationic Dyes for Synthetic Fibers

The affinity of cationic dyes is enhanced by increasing the size of the molecule and especially by introducing aromatic residues. The phenyl-substituted dye 28 is absorbed onto polyacrylonitrile materials at a higher rate than the dye 11 [25], 

Residues which make the substance more hydrophilic, such as carboxyl and hydroxy ethyl groups, lower the affinity of cationic dyes for polyacrylonitrile. Therefore, dye 29 is absorbed onto polyacrylonitrile materials much more slowly than dye 2 [26], 

High affinity may, however, lead to problems in leveling, because these dyes are bound quickly and nearly irreversibly to the acid groups of the fiber. 

Diffusibility increases with decreasing molecular mass. Dyes with a cation mass of less than 275 migrate well and are suitable for the production of level dyeings, especially in the lighter shades [27], 

Cationic dyes are also used to dye polyacrylonitrile fibers during the spinning process either from dimethylformamide solution or in the gel stage subsequent to aqueous spinning processes. 

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