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An Examination of the Mechanism of Solvent-Assisted Dyeing by Surface-Tension and Monolayer Measurements

Giles, Charles H., McIver, Norman
air, benzyl alcohol, butanol, chemical bonding, dyeing, fabrics, hydrophobicity, isopropyl alcohol, methanol, micelles, reactive dyes, solvents, surface tension, textile fibers, viscosity, wool
Surface-tension measurements of three wool-reactive dyes in water-benzyl alcohol mixture show that, contrary to previous hypotheses, the presence of the organic solvent depresses the concentration of dye at the interface with air, and most probably with wool. It is suggested that this effect accelerates dye diffusion into the fiber by reducing “drag” of diffusing dye molecules in the intermolecular channels of the fiber. Determination of surface pressure/area relationships and surface-film viscosity measurements at measured times after spreading protein monolayers on acid solutions of the same dyes in pure water and solutions of dimethyl formamide, methanol, isopropanol, n-butanol, and benzyl alcohol, respectively, shows that the presence of solvent accelerates covalent bond formation between dye and protein. It is suggested that the solvent shields hydrophobic regions of the protein and allows easier access of the dye to the reactive polar groups in the protein; also, it may retard the side reaction of dye with water. This accelerative action may not be important in dyeing with nonreactive dyes, because the ion-ion reaction between these and the fiber is probably much more rapid than the covalent bond formation of the reactive dyes. It is suggested that to accelerate dyeing, dyebath assistants should be surface-active but not likely to form mixed micelles with dye.