The change in physical properties of nylon 6 fiber dyed with a disperse dye was investigated using stress-strain curves, dynamic viscoelastic measurements, differential scanning calorimetry, and densiy measurements.
The initial rise and stress of the yield point, which follows the slope of initial rise of the stress-strain curve, were greater for the dyed fiber than they were for the control. At the same time, it was observed that in the case of dyed fiber, the shrinkage in fiber length which occurred during processing was suppressed more and the crystallinity increased more, compared to the control. The phenomena might be closely related to each other.
The tendency mentioned above was much clearer in the case of fiber treated with a higher drawing ratio. Although the amount of dye molecules absorbed into the fiber was almost the same for all dyed specimens, the induced changes in properties varied with the drawing ratio. Therefore, it could be assumed that induced changes in properties were not only due to the existence of the dye molecules in the fiber, but also to the structural change produced during the dyeing process.
When the dyed fiber was compared with the control, it was found that the temperature at which the storage modulus E' begins to drop shifted to the lower side, and a higher storage modulus existed in the rubbery elastic state. These results suggest that the dyeing treatment gives rise to a kind of structual separation in the amorphous region, that is, some amorphous regions consisting of loose packing molecules relax to a much looser packing state and some amorphous regions of close packing molecules result in a much closer, higher enthalpic packing state or crystallization. In other words, the dye molecule during the dyeing process, in cooperation with the thermal activation in the wet state, might play an important role in accelerating the moleculer movement of the polymer chain in the amorphous state and lead to structual separation as described above.