Effect of some organic acids on the diffusion of orange II in nylon 66

The sorption of sixteen organic acids by nylon yarn has been studied at 30°C. and the isotherms were found to fit the empirical Freundlich equation. Heats of sorption indicated that the acids are probably sorbed by physical solution in the amorphous regions of the polymer. The effects of some of these acids on the diffusion coefficient, equilibrium sorption and activation energy of diffusion of orange II in nylon film have been determined. Benzoic acid and salicylic acid were found to act as “swelling agents” and increase the diffusion coefficient of the dye, while β‐naphthalenesulfonic acid and p‐toluenesulfonic acid had no marked effect on the diffusion constant. The effects of the acids in reducing requilibrium dye sorption were found to be dependent on the dye‐like character of the acid concerned. All of the acids increased the activation energy of diffusion for the dye, so that the increases in diffusion coefficient were attributed to increase in entropy of activation.