Acid Dyeing of Wool

Abstract

The nature of the attraction of dyes for textile fibers, how the dyes go on, and what makes them stick so that they resist washing should be explained by any theory of dye ing. Such a theory must also be capable of predicting the effect on the transfer of the dye from bath to fibers of such factors as the amounts of each acid, dye, and salt present in a complicated solution—the dyebath. Earlier papers by Research Associates of The Textile Founda tion, demonstrated that different strong acids including acid dyes combine with wool to very different extents. This new paper describes experiments that contribute to a better understanding of the more complex equilibria which obtain in more complicated baths.

Formation by formaldehyde of a cross-link between lysine and tyrosine residues in wool

“…Such compounds are, however, very unstable, and after removal of the formaldehyde they immediately dissociate. In the case of wool, all the e-amino groups of lysine react in this way with a 10 % (w/v) formaldehyde solution almost instantaneously at room temperature (Steinhardt, Fugitt & Harris, 1946). This reaction is completely reversed on washing the wool with water, and would therefore not have been detected by Stoves (1943) or Middlebrook & Phillips (1942).…”

Analysis of the selective combination of wool with acids in mixtures

“…Th e pssential I feature of these data is the closeness with which they parallel data obtained with the pure dye acid [6]. This similarity depends very critically on maintaining an exact equivalence between the two com-I ponents of the mixture: if even small excess amounts of acid are present, considerably lower pH values are found, because the pH is then lalgely determined by the excess amount of acid of relatively low :affinity.…”

“…It is apparent that all of the methods give comparable results and that most of these results are fairly close to the experimental values. This comparison is made clearer in figure 1 of an earlier paper [6], in which the values given by eq 4 and ' 5-are plotted together with the experimental data. The values obtained from the equations all tend to be higher than those found ' experimentally, but they agree in their general trend and in the position, with respect to the pH coordinate, of the maximum amount bound.…”

“…Unfortunately, a clear-cut limit is never r ealized because of the additional combination with acid which sets in at low pH. A third and most direct method of calculabng r is to calculate the actual amounts of each anion bound: (6) where at and a2 are given by eq 4.…”

“…It is shown elsewhere that wool, immersed in mixtures of two strong acids, or ot one acid and a salt of a second, combines with these acids in unequal amounts [6).2 When present in initially equimolar mixtures with either hydrochloric acid or naphthalenesulfonic acid, such a dye as Orange II is transferred from the solution to the fibers more completely than when the dye acid alone is used. This effect is more pronounced in the presence of hydrochloric acid, which has a very low affinity for the fibers [1 , 4, 5], than with naphthalenesulfonic acid, which has a considerably higher tendency itself to combine with wool.…”