Interaction of simple acids with nylon. Part 2: Diffusion of simple acids

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Abstract
The paper deals with the diffusion of two mineral acids, hydrobromic and sulfuric acids, and two simple dye acids, NOG (C. I. Acid Orange 7) and SY (C.I. Food Yellow 3), in water‐swollen nylon 66. Anion self‐diffusion coefficients were obtained by radiotracer techniques. The bromide ion and the SY anion self‐diffusion coefficients show very little variation with concentration in the amino‐dyeing region, whereas the H2SO4 and NOG anion diffusion coefficients are concentration‐dependent. The variation of the H2SO4 anion diffusion coefficient with concentration is consistent with the formation of small quantities of the highly mobile bisulfate ion. The low SO4 diffusion coefficient may be explained by the interaction of this ion with single, fixed sites in the polymer. The variation of the NOG anion diffusion coefficient with concentration does not follow a simple D = D0[1/(1 − θ)] relationship at intermediate concentrations but the rapid increase observed as the available sites became saturated, i.e., as θ → 1, is consistent with a site saturation model.