SOLVENT EFFECT ON DYEING BEHAVIOR OF NYLON-6 WITH ACID DYES

Equilibrium uptakes of Orange II on nylon 6 fiber from sixteen protic or dipolar aprotic solvents, were determined in the presence and absence of acid at 50°C. Seven monocarboxylic acids were used.In a series of protic solvents, the dye uptake in the absence of acid decreased with decreasing dielectric constant (D) of the solvent at first, then increased. Plots of the dye uptake against l/D indicated a minimum at l/D_??_25. Addition of the acid increased the dye uptake markedly and the effect increased with decrease in pKa of the acid. In the presence of monochloroacetic acid, which was a most effective acid, the dye uptake decreased with decrease in the value of D.These results were interpreted in terms of the change in the dyeing mechanisms due to the polarity of the solvent; ionic interaction between the dye and the substrate plays an important role in the solvents having higher value of D, although the role of dipole interactions (polar van der Waals force) becomes predominant in the solvent having lower value of D. However, in spite of the high D value, the dipolar aprotic solvents other than nitriles inhibited the dye absorption by nylon. The difference in the dyeing behaviors between the nitriles and the other aprotic solvents was interpreted in terms of difference in π-conjugation of the solvents.