Interactions Between Dye and Fiber

During dyeing a pH below 2.4 should be avoided, because fiber damage occurs at low pH. 

The amorphous regions are present in the glassy state at lower temperature, and the mobility of chain segments begins only above the glass transition temperature 7 g. In the presence of water, 7g lies below the dyeing temperature for PA and hence has no influence on the course of dyeing. 

The binding of dyes to polyamide is based on various interactions [98, p. 270 ff.]. 

The amount of dye bound at equilibrium decreases with increasing number of sulfonic acid groups in the dye molecule due to increasing hydration. For this reason, mono- and polysulfonated acid dyes should not be used together in combination dyeings. 

Amino groups of the fiber can participate as ligands in the coordinate bonding of 1 1 metal-complex dyes. This is, however, of little practical importance. In addition, they can form covalent bonds to reactive dyes. 

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