聚偏二氟乙烯中空纖維膜之結構設計研究

Investigation of the morphology design of polyvinylidene fluoride hollow fiber membrane

馬良智(Liang-Chih Ma)

指導教授 ： 賴君義 ； 蔡惠安

中原大學/工學院/化學工程學系/碩士(2007年)

https://doi.org/10.6840/cycu200700392

摘要

中文摘要

本研究係以乾濕式紡絲法製備聚偏二氟乙烯(PVDF)中空纖維膜，藉由中空纖維膜外表面受水氣誘導式相分離之影響，去除外表面緻密皮層。並利用溶劑水溶液為芯液，降低內表面相分離速率，增加內表面孔隙度，達到多孔性PVDF中空纖維膜結構設計之目的。

研究中改變溶劑系統，探討溶劑對水氣誘導式相轉換過程中成膜機制之影響。研究結果發現，以N-methyl-2-pyrrolidinone (NMP)為溶劑利用水氣誘導式相轉換法製備PVDF平板膜，由於鑄膜液黏度較Triethyl phosphate (TEP) 為溶劑者低，且NMP對水氣有較大之吸收量，造成鑄膜液固化時間較長，導致以結晶主導其成膜過程而產生顆粒狀結構。

利用乾濕式法製備PVDF中空纖維膜發現，增加氣距長度延長初生中空纖維膜與水氣接觸時間，可製備出多孔性PVDF中空纖維膜。其最佳紡絲條件為氣距長度100cm且芯液組成為50wt%溶劑水溶液。若以NMP和TEP為溶劑所製備之中空纖維膜其外表面孔洞直徑分別為1μm與0.9μm，而外表面孔隙度則分別為50.6%與40.9%。但利用孔隙測定儀所量測之平均孔洞直徑分別為0.33μm與0.24μm，相近於內表面平均孔洞直徑，表示內表面為主要透過阻力。利用顯微鏡接觸角量測儀量測中空纖維膜外表面對水接觸角發現，其接觸角都大於120°，表示外表面多孔性結構有助於疏水性質之提升。研究中利用冷凍萃取之方法觀察初生中空纖維膜在氣距過程結構變化，結果發現在氣距過程中薄膜外表面受水氣之影響已有孔洞結構之生成，且隨著氣距長度增加其表面孔洞有增加之趨勢。

本研究也針對水氣誘導式相轉換過程對於PVDF結晶性質做探討。研究結果發現，在NMP溶劑系統製備平板膜時，隨著水氣曝露時間之不同其結晶型態會轉變。但對於TEP為溶劑之系統其結晶型態並無改變。利用乾濕式法製備PVDF中空纖維膜，隨著氣距長度之增加其薄膜結晶度隨之提升，且結晶型態也有所改變，很有可能受到水氣及重力所誘導之順向作用力影響所導致。

關鍵字

中空纖維膜 ； 水氣誘導式相分離 ； 成膜機制 ； 結晶 ； 聚偏二氟乙烯

並列摘要

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.

並列關鍵字

hollow fiber membrane ； membrane formation mechanism ； polyvinylidene fluoride ； crystal ； vapor induced phase separation

參考文獻

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