Relations between Dye Diffusion and Fiber Structure in Nylon 6

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Abstract
Diffusion rates of an acid dye into commercially drawn Nylon 6 yarns were measured and are discussed in relation to fiber structure. The yarn samples investigated were drawn at two different draw rates and various draw ratios up to 3times;. A four-fold decrease in dye diffusion was found as the draw ratio increased from 1X to 3×; this decrease was not monotonic, however. Maxima and inflections occurred in plots of the diffusion constant vs. draw ratio. The dynamic loss modulus E″, measured under the dyeing conditions, exhibited similar maxima; E″ is indicative of the mobility of the amorphous chain segments. Taken with birefringence measurements, the data are interpreted as indicating a structural breakup during drawing of the undrawn yarn, resulting in an overall less stable microstructure in draw-ratio regions where maxima or inflections occur in the diffusion rate. This instability is markedly affected by drawing rate.