EFFECT OF SALTS ON PHYSICAL INTERACTIONS IN WOOL DYEING WITH ACID DYES

The modified Donnan model, which considers the dye distribution coeffi cient as a function of salt concentration and property in the dyebath, is used to describe the dyeing behavior of wool with acid dyes and di fferent kinds of salts. This modification is based on the understandin g that salt anions are either kosmotropes (water-structure maker) or c haotropes (water-structure breaker). They affect the free energy of th e dyebath through their influence on water structures. As is well know n, adding salt to the dyebath decreases dye sorption due to its reduct ion of ionic attraction between negatively charged acid dyes and posit ively charged wool fibers. However, adding some salts such as sulfate and dihydrogen phosphate can increase dye sorption if the salt concent ration is high. This phenomenon cannot be explained by the classic the ory of salt functions in dyeing. The modified Donnan model is used to explain quantitatively both the decrease and increase of acid dye sorp tion on wool with increasing salt concentration.