Effects of Temperature, Dope and Precipitation Bath on the Morphology of the PVDF Membranes

• Main Authors: Fang, Lin, 方菱
• Other Authors: Liao-Ping Cheng
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/00889369779724791572

碩士 === 淡江大學 === 化學工程學系 === 86 === The mechanism of poly(vinylidene fluoride) (PVDF) membrane formation by isothermal immersion-precipitation method was studied. During the process, phase separation might either be initiated by liquid-liquid demixing or crystallization. Depending upon the preparation conditions (e.g., the dope and bath concentrations and the system temperature), dominance of these phase separation processes differed; thereby affected the structure of the formed membranes. Both the thermodynamic and the kinetic aspects were considered for the membrane formation systems : water/dimethyl formamide/PVDF and 1- octanol/DMF/PVDF. The phase diagrams of these systems in different temperatures provided the information of the effects of temperature on the membrane structure, whereas diffusion trajectory and concentration profile computations yielded the effects of the dope and bath conditions. For PVDF precipitation from 1-octanol/DMF solutions, because mass transfer was slow, rather than exhibiting an asymmetric structure, the membrane was uniform composed of interfused spherulites. For the water/DMF/PVDF system, various structures characterizing different degrees of dominance of liquid-liquid demixing and crystallization in the precipitation process could be prepared by adjusting the solvent content in the bath. Based upon experimental results and theoretical analysis, we have a better insight into the formation mechanism of the PVDF membranes in this research.