Abstract
Investigation of the temperature dependence of the coefficients of diffusion for dye in untreated and solvent-treated polyester yarns has shown that solvent treatments that increase dyeability do not change the dye-diffusion mechanism. The free-volume mechanism, which depends on polymer segmental mobility for the transport of dye through temporary holes, is operative in solvent-treated as in untreated polyester. The significant increase in dye-diffusion coefficients resulting from solvent treatment is attributed to increased segmental mobility in noncrystalline domains of the treated fiber. This increased segmental mobility is reflected in lowered α-dispersion temperatures, as determined from dynamic mechanical properties. Treatments with dimethylformamide and heat treatments at temperatures approximately 80°C higher both yield polyester yarns that have the same segmental mobility, as indicated by dynamic mechanical measurements, but the saturation dye uptake in the solvent-treated yarns is much higher. This increased amount of dye is believed to be held in voids in the fiber structure formed during solvent treatment. Diffuse scattering in small-angle x-ray diffraction patterns of solvent-treated yarns has been taken as evidence for the existence of such voids.
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