|摘要: ||本研究冷溶劑誘導相分離法(cold solvent induced phase separation, CIPS)製備尼龍-12薄膜，與一般濕式相轉換製膜法的不同在於，沉澱液使用的是用來配製膜液的溶劑，它在浸漬沉澱過程中不會有濃度改變的問題，不像濕式法必須不斷更新沉澱液來維持濃度，造成溶劑浪費及破壞環境的問題，另一方面也增加成本負擔，本研究使用純甲酸作為沉澱液，並藉由控制製膜液之熟化溫度、熟化時間及沉澱液溫度等操作變因，使製膜液的晶核數目、黏度增加，改變孔隙度大小和結構，以及增強薄膜強度。當製膜液經過適當的熟化(45℃，2小時)，薄膜結構產生束狀結構之互穿雙連續多孔薄膜，其結構、孔隙度和孔洞尺寸以及薄膜抗張強度互相影響，孔隙度約為60~40%之間，並由DSC和XRD的測量得知，尼龍-12薄膜的熔點約為167℃，薄膜為α與γ型態的結晶結構，結晶度約為27%，且薄膜上表面之接觸角達100o以上，為疏水型薄膜，可用於薄膜蒸餾與微過濾等分離程序。本研究利用CIPS法所製備之尼龍-12薄膜進行薄膜蒸餾之分離程序，以3.5wt%之食鹽水溶液進行淡化，其阻隔率皆可達到99%以上，分離效果相當良好，並且最高之通量約為5 LMH，與相同條件下進行MD測試之市售PTFE、PVDF等薄膜進行比較，探討薄膜結構間的差異對薄膜蒸餾的影響進行探討，分別以電子顯微鏡(SEM)及影像分析軟體(Image J)，分別觀察薄膜的型態結構以及分別計算上、下表面及截面的孔隙度，其中市售之PVDF薄膜之孔隙度與尼龍-12薄膜相近，但尼龍-12薄膜成束狀互穿的多孔型結構，與具有巨孔型之液胞且皮層結構較為明顯之PVDF薄膜相比，其穿透性以尼龍-12薄膜較高，其通量已高過PVDF-C之通量(3 LMH)，因此可知薄膜結構對薄膜蒸餾的效率具有相當的影響。|
In this research we focused on investigation of the formation of polyamide 12 (PA12) flat-sheet membrane by cold-solvent induced phase separation (CIPS) process. CIPS was different from traditional immersion precipitation method. Because the cold precipitation bath (in this research we use formic acid FA) could keep its concentration during the immersion process, it could be used repeatedly. In addition to dope’s concentration and bath temperature, we also found that aging is an important factor that affected membrane formation. This was because aging could create nuclei in the dope, which lead to significant decrement of particle size in the formed membranes. When the aging temperature was set at 45 oC (bleow the crystallization line) and bath temperature at 10 oC, the membrane exhibited a particulate bi-continuous structure. The water permeation flux and tensile strength of the membrane were measured and the results indicated that they were correlated with the porosity, pore size, and membrane morphology. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses indicated that the membranes had crysrallinity of ~27% and DSC data showed that all membranes had a similar crystal melting behavior with Tm close to 167 oC.
Prepared PA-12 membranes, together with commercial PTFE and PVDF membranes, were applied in direct contact membrane distillation (DCMD) processes to separate NaCl aqueous solutions. The highest permeation flux of PA-12 membrane that could be reached was 5 LMH and at this flux the rejection was > 99%. Compared with the tested commercial PVDF membrane, which has a similar pore size to the PA-12 membrane, but different porous structure - commercial PVDF had a denser top surface and a cross section composed of macrovoids and closed cellular pores. Therefore, its highest permeation flux was 3 LMH smaller than the PA-12 membrane. As to the commercial PTFE membrane, the porosity was 80%, the thickness was only ~50μm, and the pores are well interconnected. Therefore, water vapor could pass through the membrane easily, and the highest permeation flux reached 13 LMH. In other words, membrane structure had great influence on the performance in DCMD processes.