| Summary: | 碩士 === 淡江大學 === 化學工程與材料工程學系碩士班 === 101 === Microporous Nylon-66 membranes were prepared by non-solvent induced phase separation (NIPS) from the Water/1-Butanol/Formic acid/Nylon66 quaternary system. Water, as a strong non-solvent for Nylon-66, was employed to enhance polymer crystal nucleation in the casting dope, while 1-butanol was adopted as a soft coagulant whereby liquid-liquid demixing mechanism can be sufficiently suppressed. By gradually increasing the water content in the dope, the effect of nucleation density on the morphology of the membrane was clearly manifested. While low water content (<2.5%) dopes resulted in membranes consisting of large full spherulites, high water content (>7.5%) dopes gave rise to symmetric bi-continuous membranes composed of small interlocked, stick-like crystallites intertwining with continuous channels of micropores. Water permeation flux and tensile strength of the membranes were measured and correlated with the porosity, pore size, and membrane morphology. In addition, X-ray diffraction (XRD) and Fourier Transform Infrared-Attenuated total reflection (FTIR-ATR) analyses indicate that the membranes contained a-type crystals with a crystallinity of ~38 %, consistent with that determined from Differential Scanning Calorimetry (DSC). The later method also showed that all membranes have a similar crystal melting behavior with Tm ~265 oC.
PVDF membranes are prepared via immersion precipitation method. The effects of Tween20 additive in casting dope on the membrane structure and ultra-filtration performance have been studied subsequently. We used field emission scanning electron microscope (FESEM) to observe the morphologies of the membrane cross-section, top and bottom surfaces. The results indicated that the structure of the crystalline particles changed from sheaf-like to stick-like shape and that the finger-like macrovoids and the nano-pore on the top surface became more obvious as the amount added Tween20 increases. Also, we utilized tensile strength measurements to determine the mechanical property of membranes. The residual Tween20 in the membrane was analyzed by contact angle measurement, Fourier Transform Infrared-Attenuated total reflection (FTIR-ATR), Nuclear Magnetic Resonance (NMR) and X-ray Photoelectron Spectrometer (XPS), and we found that the surfactant has almost been removed completely. The water flux and ultra-filtration experiments showed that the membranes exhibit both relatively high permeability and selectivity.
At last, capillary membranes were fabricated by both the wet spinning and dry-jet wet spinning methods. The issues of Tween20 additive in casting dope and air gap have been investigated. We used scanning electron microscope (SEM) to observe the morphologies of cross-section, external and inner surface of the formed capillary membranes. The results showed that pore size and porosity of the external and inner surface increased, the shell side and lumen side of macrovoid structure was enhanced, and the structure of spherulite changed from sheaf-like to stick-like with increasing the amount of surfactant in the casting dope. The mechanical property and the viscosity under different shear rate were determined by tensile strength and rheometeic measurements we found that the viscosity of casting dope increased and tensile strength of membranes decreased with increasing the surfactant in the casting dope. Furthermore, the results of Fourier Transform Infrared-Attenuated total reflection (FTIR-ATR), contact angle measurement and Nuclear Magnetic Resonance (NMR) revealed that the residual quantity of Tween20 in the capillary membranes is only about 0.3% after a series of washing steps.
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