Effect of Fiber and Dyebath Variables on the Rate of Acid Dyeing of Nylon 6,6

The results of an experimental study of the effects of several variables on the acid dyeing of nylon are presented. The dyeing rate was directly proportional to the number of amino-end groups (dye sites) in the fiber for the two dyes tested; the dyeing rate approached zero as the number of dye sites approached zero. The dyeing rate was the same for samples with viscosity average molecular weights of ∼25,000 and 30,000, but was somewhat higher for a ∼22,000 M_v sample, as might be expected from the dependence of other properties on molecular weight. The dyeing rate is shown to be linearly related to 1/√ d, where d is the denier per filament. The molecular size of the acid molecule used in the acid dyebath was investigated, and no effect was found for formic, acetic, propionic, and hexanoic acids. An effect is found on both rate and saturation, however, if the larger and more polarizable napthoic acid is used. Sodium chloride and sodium sulfate, when added to the dyebath, decrease both the dye absorbed at saturation and the rate of dye diffusion, although they offer benefits as leveling agents. The effect of sodium chloride is considerably greater than for sodium sulfate.