The Relation Between the Number of Sulphonic Groups in Acid Dyes and the Yield Stress of Dyed Nylon Monofilament

Abstract

Studies have been made of the relation between the number of sulphonic groups in acid dyes and the yield stress of dyed nylon monofilament. The three dyes—mono-, di-, and tribasic azo dyes, which have α-naphthylamine → β-naphthol as a skeletal structure—were applied to nylon filament in a range of concentrations, and the yield stress of the dyed one was measured.

The yield stress of the dyed nylon filament is larger than that of undyed one. It increases with increase in the dye concentration in the filament. But the effect seems to be much smaller when dyeing takes place on the terminal amine groups than when overdyeing. The concentration of dye in the filament in which the amine groups become saturated decreases with increasing sulphonation, so that in the same concentration of dye in the filament the yield stress increases with increasing sulphonation, and apparently the number of sulphonic groups seems to have an effect on the yield stress.

But the careful treatment reveals that the net effect of dyes on the yield stress is independent of the number of sulphonic groups in dyes. This suggests that a polybasic dye behaves as a monobasic one in a region of overdyeing.