|Abstract: ||本研究首先利用冷溶劑誘導相分離法，由聚乙烯乙烯醇/1,3-丙二醇兩成分系統製備多孔型聚乙烯乙烯醇薄膜，並藉由改變沉澱槽之溫度及刮刀之厚度，探討此二參數對薄膜結構與物性的影響。當沉澱槽溫度落在結晶線之下及液-液分相線之上時(45℃)，薄膜呈現微粒狀結晶結構，而落在spinodal分相曲線內部時(25℃)，則呈現雙連續網狀結構且有些許微粒結晶之特徵，當更深入spinodal區域時(5℃&-20℃)，則呈現單純雙連續網絡結構。以不同厚度刮刀塗佈製膜液並浸漬於5℃沉澱槽時，其薄膜結構皆呈現典型之spinodal decomposition所產生之雙連續網絡結構。而各項分析結果皆指出，水通量、水滲透時間與機械強度的測量結果和薄膜的型態、孔隙度和孔徑大小有關，此外，藉由XRD和DSC等儀器分析，測得薄膜結晶度大約在38~42%左右，並由DSC的測量得知薄膜的熔點為~184℃。本研究接著選用聚偏二氟乙烯/磷酸三乙酯(TEP)/純水三成分系統，結合了非溶劑誘導相分離法及熱誘導式相分離法兩種製膜法之特點，在相圖上找到一個特殊的製膜液組成，使得製膜液內溶劑/非溶劑以及沉澱槽溶劑/非溶劑之比例相同，成為循環使用槽(reusable bath)，並利用其製備聚偏二氟乙烯多孔型高分子薄膜。藉由改變沉澱槽之成份以及刮刀之厚度，製作出一系列不同孔隙結構之薄膜，探討其物性及其過濾之效率。以reusable沉澱槽所製備之薄膜無皮層的產生，而以純水、30wt% TEP及60wt% TEP之沉澱槽所製備之薄膜皆有皮層生成，隨著沉澱槽TEP濃度的提升，皮層呈現越來越薄之趨勢。而皮層的厚度影響薄膜之孔隙度與機械強度，皮層越薄，孔隙度隨之提升，使得機械強度減弱。當以不同厚度刮刀塗佈製膜液並浸漬於reusable沉澱槽時，我們可從FE-SEM影像圖發現，隨著刮刀厚度越薄，其薄膜結構越趨向於蕾絲結構之型態。此外，藉由DSC的測量得知薄膜的熔點為~159℃，並由XRD的分析得知薄膜結晶度大約在63~64%左右。由水通量與過濾實驗得知，以reusable沉澱槽所製備之薄膜具有相當高的通量和良好之阻隔率。|
The purpose of this study is to investigate the effect of bath temperature and casting thickness on the preparation of membranes from EVOH/1,3-propanediol binary mixture system via the cold solvent induced phase separation (CIPS) process. When the temperature of the precipitation bath (45℃) was below the crystallization line and above the liquid - liquid phase separation line, the membrane exhibited a crystalline particulate structure; when the bath temperature (25℃) was just below the spinodal decomposition temperature, it presented a bi-continuous network structure and bore slight crystallization characteristics of particles; when the bath temperature (5℃&-20℃) sit deeply in the spinodal zone, it presented a pure bi-continuous network structure. With different casting thickness and immersed in 5℃bath, the formed membranes all presented bi-continuous network structure typically arising from spinodal decomposition. The water permeation flux, wettability and tensile strength of the membranes were measured and the results indicated that they were correlated with the porosity, pore size, and membrane morphology. In addition, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses indicated that the membranes had crystallinity of 38~42 %. The DSC data also showed that all membranes had a similar crystal melting behavior with Tm close to 184℃.
We then chose the poly (vinylidene fluoride)/triethyl phosphate/water ternary system and used a method that combined features of non-solvent induced phase separation (NIPS) and thermal induction phase separation (TIPS) to prepare porous PVDF membranes. In the phase diagram we found on a special dope composition such that the solvent/non-solvent ratio in the dope was equal to that in the precipitation. Therefore, the composition of the bath could be held constant by itself, and the bath can be used repeatedly (termed reusable bath). By varying the composition of the precipitation bath and casting thickness, a series of membranes with different porous structures were formed. The effects of the membrane structure and filtration performance have been studied subsequently. Results showed that when water, 30wt% TEP and 60wt% TEP were used as the precipitation bath, the membrane presented a skin layer at the top surface. In contrast, when precipitation in the reusable bath, it did not show a skin layer near the top, and with increasing of the TEP concentration in the bath, thinner skin layer tended to form. The thickness of the skin layer was found to affect the porosity and mechanical strength of the membranes; the thinner the skin, the higher the porosity, and thus the lower the mechanical strength. When films with different thickness were immersed in the reusable bath, we found from the FE-SEM images that thinner casting thickness tended to yield membranes that bore lacy structure. In addition, DSC measurements showed that the melting points of the membranes were ~159℃, while XRD analyses indicated that the crystallinity of membranes was about 63 to 64%. The water flux and filtration experiments showed that the membranes prepared from the reusable bath exhibited both high permeability and selectivity.