Interactions of Nonaqueous Solvents with Textile Fibers

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Abstract
The thermal stability of heat- and dimethylformamide (DMF)-induced structural modifications in polyester yarns has been investigated by differential scanning calorimetry (DSC) and other techniques. While heat treatments produce a characteristic, sharp, premelting endotherm peak (PEP) at temperatures slightly above the treatment temperature, DMF treatments show a broad, diffuse PEP in their DSC curves at approximately 70°C above the treatment temperature. The appearance of a characteristic diffuse PEP in the DSC curve suggests the formation of crystallites with a wide distribution of thermal stabilities which only partially stabilize the swollen fiber structure. Small-angle x-ray scattering (SAXS) studies show that subsequent heat treatments even at low temperatures (120°C) cause a partial collapse of the void structure observed after a high-temperature solvent treatment. The partial collapse of the void structure is also reflected in decreased dyeability and increased density of the polyester fibers but has no effect on polymer segmental mobility, as indicated by the unchanged α-dispersion temperature. It is therefore suggested that the observed decrease in dyeability after subsequent heat treatments of DMF-treated polyester yarns is associated with the disappearance of the voids. The high levels of saturation dye uptake observed in fibers with a void structure appear to be due to an increase in the internal surface within the fiber structure and/or to the ability of dye molecules to form clusters in these voids. Thermal aftertreatments of dyed, void-containing fibers should also result in a collapse of the void structure, which might effectively entrap dye molecules in the fiber structure and consequently lead to high wash- and drycleaning-fastness.