Sorption isotherms and dyeing rates of purified disperse dyes on polyester microfibers (fineness of 0.25-1.0 denier) from water have been measured at 95°C. The isotherms are curved and well described in terms of the dual-mode sorption model: Nemst-type partitioning and Langmuir sorption are concurrently operative. The effect of a diffusional boundary layer on the dyeing rate is small under the conditions; the microfibers were dyed in the form of a bulky two-ply yarn in a well stirred bath. Dyeing rates of a commercial dye are also measured at 110 and 130°C. For dyeing of a 0.32d fiber at 130°C, the amount of dye sorbed by the fibers attains a maximum value at an early stage and then decreases gradually. This phenomenon is explained in terms of the aqueous solubility of very fine dye particles. The relation between dye sorption behavior and the fine structure of the microfibers is discussed.

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SYNOPSISUltrahigh speed spinning of poly (ethylene terephthalate) (PET) was carried out at various take-up velocities from 5 to 10 km/min. The superstructure of as-spun fibers was characterized by small-angle X-ray scattering (SAXS) , wide-angle X-ray diffraction ( WAXD), viscoelastic properties, and scanning electron microscopy (SEM) . Above 6 km/min the peaks or shoulders that are due to the interference between microfibrils appear on the equatorial SAXS intensity curves. The interfibrillar spacing estimated from the peak position increases with increasing take-up velocity. Comparison of the spacing with the lateral crystal sizes estimated from the broadness of the crystal (hkO) WAXD peaks indicates that the microfibril diameter becomes thick with increasing take-up velocity. Although the orientation and density in amorphous region for high-speed spun fibers are very low on the average, it can be seen that a few highly extended tie molecules exist in that region, and the number of these molecules increases with increasing take-up velocity. The modes and mechanisms of fibrillation induced by a rubbing test are discussed relating to these results.

It is known that the flat fiber of high aspect ratio shows the complexed crimp structure in which the wavy crimp is formed at the edge of the flat fiber as found in sea-weed. The mechanism for the formation of crimp structure in the flat fiber of poly (ethylene terephthalate) was studied in this work. The degree of crimp increased with increasing aspect ratio and spinning speed. The birefringence of this com plexed wavy crimped yarn showed the large distribution along the long axis of the fiber cross section. When the fiber shrank by heat treatment, the structural heterogeneity caused the irregularity of shrinkage which developed the wavy crimp.

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