STUDIES ON THE DYEING PROPERTIES OF ACID AZO DYES (PART IV)

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Abstract
The adsorption by 6-nylon at neutral and alkaline region of acid azo dyes having α-naphthylamine →-β-naphthol as the skeletal structure has been measured. The amount of equilibrium adsorption of these dyes at pH range higher than that of isoelectric point of 6-nylon is unexpectedly large, especially monosulphonic acid dye (naphthionic acid→β-na-phthol (Dye II) have considerable adsorption, 2.2×10-2m mole/g fibre, even at pH 10. (Table 1, Fig. 1) On the other hand, the adsorption is lineary dependent on amino end-group content of the fibre, even at pH 10 (Table4, Fig. 3). Linear extrapolation in this relation (Fig. 3) gives the adsorption of dye at zero amino end-group content, 2.5×10-3m mole/g fibre, which is equal to the adsorption value of skeletal structure, α-naphthylamine→β-naphthol. (Table 2, Fig. 2) One of the explanations of these facts is as follows; adsorption by nonpolar force contributes to the dyeing of these dyes, but the main part of the adsorption is attributed to the salt-linkage between dye anion and the basic site of the fibre. At higher pH than isoelectric point of 6-nylon, and even at alkaline region, e. g. pH 10, the formation of the salt-linkage takes place.

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