The liquid-liquid phase equilibria for the hexane polydisperse polyethylene (PE) systems were measured at 473 K and at feed PE weight fractions ranging from 0.075 to 0.20. An apparatus was developed for the measurement, which consisted of a variable-volume optical cell and two sampling tubes for correcting both the top (hexane-rich) and bottom (PE-rich) phases. The PE weight fraction of the hexane-rich phase decreased with decreases in the feed weight fraction of PE and the phase equilibrium pressure. On the other hand, that of the PE-rich phase increased as the feed PE weight fraction and pressure decreased. Furthermore, the experimental data were compared with the predicted results obtained using the Sanchez-Lacombe equation of state. The predicted results approximately reproduced the experimental results for the PE weight fractions of the hexane-rich phase. Although some deviations were found in the experimental results of the PE-rich phase, the predicted phase equilibrium lines qualitatively reproduced the experimental results, which showed that the PE weight fraction increased with decreases in the feed PE weight fraction and pressure. Moreover, both the experimental and the predicted results also indicated that the in uences of the feed PE weight fraction on the weight average molecular weight and on the polydispersity index of PE in the PE-rich phase were larger than those in the hexane-rich phase at low pressure.
The micromolding process using biocompatible thermoplastic polymers is highly attractive as a fabrication process of microdevices in biomedical applications. In this study, we investigated the effect of the thermal history in the micromolding process on the crystallinity of semi-crystalline polymers, such as poly (L-lactic acid) (PLLA), during their crystallization from the amorphous and molten states. In particular, the thermal history in the micromolding process using poly(dimethylsiloxane) replica mold embedded with a thermocouple was recorded. The crystallinity of PLLA constructs fabricated using the micromolding process was measured via wide-angle X-ray scattering, and crystallization kinetics was analyzed based on the Kolmogorov–Johnson–Mehl–Avrami equation. A crystallization rate of k = 0.061 min−n was obtained in the micromolding process of PLLA crystallization from the amorphous state, accompanied by the quenching operation, forming a large number of crystal nuclei. Finally, the fabrication of PLLA microneedles was performed using micromolding processes with different thermal histories. The information about the thermal history during the micromolding process is significant in the development of polymer microdevices to achieve better material properties.
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