| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 95 === Abstract
In this study, polyvinylidene fluoride (PVDF) hollow fiber membrane was spun via dry-wet spinning method to eliminate the outer dense skin layer by vapor induced phase separation (VIPS). In addition, aqueous solvent solution was used as the bore liquid to increase inner surface porosity. So that it could achieve the objective of porous morphology design.
The membrane formation mechanism of different solvent system in VIPS process was discussed. The results revealed that the polymer solution of PVDF/N-methyl-2-pyrrolidinone (NMP) had lower viscosity and higher water vapor sorption capacity than PVDF/Triethyl phosphate (TEP), resulted in the PVDF/NMP solution had longer coagulation time than PVDF/TEP. Thus, the crystallization led the membrane formation mechanism to form particle morphology.
Outer surface porosity was increased with increasing the air gap length. The optimum spinning condition for air gap length and bore liquid were 100cm and solvent(50wt%)/H2O, respectively. The average outer surface pore diameters were 1 and 0.9μm and the outer surface porosity were 50.6% and 40.9% for NMP and TEP solvent system. While the average bulk pore diameters which were measured by porosimeter were 0.33μm and 0.24μm for NMP and TEP system, respectively. It revealed that the permeate resistance was in the inner surface. By using microscopic contact angle meter to measure the hollow fiber membrane contact angle, it could be found that the contact angle were higher than 120° for different solvent system. It was showed that the porous membrane structure could enhance the hydrophobicity.
The nascent hollow fiber membrane morphology was also investigated by introducing the as-spun hollow fiber into liquid nitrogen directly after went through the air gap zone. The results show that pore structure was formed in outer surface during the air gap zone by VIPS, and the porosity was increased with increasing the air gap length.
Moreover, the crystallization property of PVDF induced by VIPS was also investigated in this study. For NMP solvent system, the crystal type of PVDF flat membranes was transformed by VIPS, while the TEP solvent system was not. The crystal type of PVDF hollow fiber membranes was also transformed for different solvent system. The crystallinity of PVDF hollow fiber was increased with increasing air gap length. This phenomenon might be due to the effect of vapor and the orientation which was induced by gravity on the transformation of the crystal type.
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