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Self-crimp polyester yarns were manufactured using a conjugated spinning process involving two parallel but attached fibers with different shrinkage properties. A theoretical model proposed by Denton proved to be very useful for predicting crimp potential. Maintaining identical or very similar melt viscosities of the two components was demonstrated to be very critical for obtaining a straight interface and eliminating the dog-legging problem. The crimp tests illustrate that the triangular shapes are superior to the round cross section. The optimum volume ratio for making a self-crimp bicomponent skein is 50/50. Moreover, the optimal fiber thickness is 8 denier per filament. Finally, this study found that the combination of PET/PTT outperformed that of PET/PBT and PET/CD in terms of crimp potential, crimp stability, and elastic recovery. This phenomenon is primarily attributed to the markedly different thermal shrinkages of PET and PTT. POLYM. ENG. SCI., 45:838 -845, 2005.

Hyperbranched polymers (HBPs) formed by the self-condensing vinyl polymerization (SCVP) or self-condensing ring-opening polymerization (SCROP) of monomer AB activated by stimuli with various reactivities were investigated by the generating function method. Two different cases were discussed: in case I, the concentration of the stimulus decayed during the activating reaction, and in case II, the stimulus acted as a catalyst to activate the monomer AB, and the change in stimulus concentration was neglected. The reduced number-and weight-average degree of polymerization (DP n *and DP w *) and degree of branching (DB) of the HBPs were found to depend not only on the mole ratio of stimulus to monomer AB (λ) but also on the reactivity ratio of the stimulus (β). The DP n *, DP w * and polydispersity index of the reduced degree of polymerization increased with decreasing reactivity of the stimulus. In case II, when λβ>1, there were only a few influences on the average degree of polymerization by λβ, and the results were similar to those of case I. However, when λβ<1, the degree of polymerization differed significantly between the two cases. The maximum degree of branching of about 0.5 was obtained with near full conversion of A, and the degree of branching depended on the amount and reactivity ratio of the stimulus.

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This work investigates the melt spinning process of the metallocene cyclic olefins copolymer (mCOC), which had never been successfully developed before. The shear-viscosity examination reveals that the mCOC has a mild shear thinning tendency due to the presence of cyclic olefins, but is very sensitive to the temperature variation. The optimal melt extrusion temperature for the mCOC is found between 320 and 330°C. The mCOC is known to have high Tg, which would cause early solidification, seriously broken filaments, and winding interruption during the melt spinning process. Accordingly, the traditional spinning process employing an air-quenching system at 18°C for polyolefins, such as polypropylene and polyethylene, is inappropriate for the mCOC. Experimental results reveal that in melt spinning of the mCOC, it is necessary to install a heating board of 1.4 meters length and heated up to 180°C to assisting with the spin draw ratio of the mCOC. The elongation rheology of the mCOC was found to be greatly affected by the presence of cyclic olefins. The optimal spinning speed is 1500 m/min. In such a speed, the spin draw ratio of the mCOC is 90, which is higher than the literature value of 10[11], but still far smaller than 200–400 for typical linear polymers. Experimental results suggest that hot drawing, with a drawing ratio of 1.15 and godet temperature of 200°C, can yield yarn with optimal tenacity of 1.4 g/den. Birefringence observations indicate that mCOC yarn, even via melt spinning and hot drawing, does not exhibit any bulk orientation. The result of X-ray diffraction implies that hot drawing can enhance the formation of nano-crystals with an average size of approximately 6.5 nm. This takes place on the short linear olefin chains among the cyclic segments. The degree of crystallization increases slightly as the godet temperature increases.

This study discusses a light-weight bicomponent hollow fiber that is formed from a low-density material on the inside, such as polypropylene (PP), and a regularly dyeable material outside, such as polyterephthalate (PET) or nylon. Finite elements and the Optimesh-3D remeshing approach are adopted to identify the main controlling factors of spinning the sheath-core hollow fiber without the consideration of winding actions are performed, based on a four-segmented arc spinneret design. The results indicate that the deflection of melt streams under the spinneret is a major factor that controls the gluing of the gap between arc segments. A greater mismatch between the viscosities of the sheath and the core causes a greater deflection and increases the likelihood of gluing events. Beyond deflection, die swelling under the spinneret is another issue of concern in the processing of bicomponent hollow fibers. Finally, the simulation results are compared with experimental data, and the most appropriate conditions for forming a PET/PP hollow fiber were obtained. POLYM. ENG. SCI., 51:704-711, 2011. ª

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A mathematical analysis model of multilayer viscoelastic fluids flowing down an inclined plane for any arbitrary wave numbers has been established to improve multilayer product quality in the coating processes. In the stability study of the free surface with small elastic force, Reynolds number is the primary parameter to induce surface instability for long and intermediate waves. When the elastic force in either layer is large, elasticity can affect the stability of long and intermediate waves. In addition, viscosity stratification across the interface can also affect the stability of the free surface. For the interfacial stability of two-layer flow system, it is found that purely elastic instability occurs in most depth ratios for the whole spectrum of waves when the fluid with elasticity is placed as the inner layer next to the solid wall. In the study of stability for viscoelastic fluids it demonstrates that arranging the more elastic and less viscous fluid as the outer layer leads to interfacial stability. In the more than three-layers investigation we found that placing the most viscous and least elastic liquid as the innermost layer next to the solid wall and the least viscous and most elastic liquid as the outermost layer next to the passive air can ensure the stability for the whole spectrum of waves.