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Highly aligned, single‐layered hollow fibrous membranes are prepared using two‐fluid coaxial electrospinning (ES). Polyethylene oxide (PEO) is used as the core, and polyurethane (PU) and blends of PU with silica (SiO2) are used as the shell to extract the PEO. The effects of the polymer‐complex concentration, the ES parameters, and the SiO2 blending ratio on the morphologies and mechanical properties of fibers are explored. Using an appropriate PU concentration and applied spinning voltage combination yields a high fiber‐alignment degree. The hollow fibrous average area increases as the inner‐to‐outer flow‐rate ratio (FRRi/o) increases because the inner flow increases. When using a PU concentration of 13 wt%, a spinning voltage of 7 kV, and an FRRi/o of 0.8, along with blending 15% SiO2 with PU, the fiber alignment of the PU/SiO2 membranes is 95%. The Young's modulus indicates that adding SiO2 enhances the mechanical properties, causing a monolayer hollow‐fiber assembly with interconnected fibers to form.

ABSTRACT:The phase transitions and the morphology of hard-segment domains of those siloxane-containing hardsegmented polyurethane copolymers are studied by differential scanning calorimetry (DSC). The NH-SiPU2 copolymer, which comprises a siloxane-urea hard segment and a polytetramethylene ether glycol soft segment (PTMG2000), exhibits a high degree of phase-separation and a highly amorphous structure. Therefore, NH-SiPU2 copolymer proceeds with a melt-quenching process and with various annealing conditions, to examine the morphologies and the endothermic behaviors of the siloxane-containing hard-segment domains. DSC thermograms of further annealed NHSiPU2 indicate that the first endotherm (T 1 ) at around 75°C is related to the short-range ordering of amorphous siloxane hard-segment domains (Region I), and the second endotherm (T 2 ) at around 160°C is related to the long-range ordering of amorphous siloxane hard-segment domains (Region II). The DSC thermograms at annealing temperatures below and above T 1 demonstrate that both the temperature and the enthalpy of T 1 linearly increase with the logarithmic annealing time (log t a ). This result shows that the endothermic behavior of T 1 is typical of enthalpy relaxation, which is caused by the physical aging of the amorphous siloxane hard segment. Additionally, the siloxane hard segments in Region I are movable, and can merge with the more stable Region II under suitable annealing conditions. Transmission electron microscopy shows that Regions I and II are around 200 and 800 nm wide, and that the Region I can be combined with the stable Region II, under suitable annealing conditions.

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