添加聚乙二醇對聚颯薄膜的孔洞結構與過濾效能之影響

Abstract

本研究主要是加入不同溶劑與添加劑製備高分子溶液，透過非溶劑誘導相分離法中的溼式法成膜，並探討薄膜的結構與其過濾效能。所使用的高分子為聚颯(polysulfone, PSF)，溶劑分別為強溶解力的DMAc與弱溶解力的2P，另外加入聚乙二醇(poly ethylene glycol, PEG)作為添加劑。實驗部分總共分三個階段：無添加劑系統、添加劑系統與共溶劑系統。 第一階段為無添加劑系統，PSF/DMAc製備出的薄膜結構為表面緻密並伴隨著多個巨型孔洞，PSF/2P則在上層出現海綿狀結構，由於海綿狀結構有高連通性的特點，使2P系統有較高的透過率。 第二階段則是在兩個不同溶劑系統加入不同濃度與不同分子量的PEG，從流變性質可以看出隨著PEG濃度與分子量的上升，鑄模液黏度也隨之提高。在PSF/DMAc/PEG系統裡，PEG能有效的打通巨型孔洞間的孔壁，而提高薄膜的透過率，這個現象隨著PEG分子量上升有更顯著的影響；而在PSF/2P/PEG系統中，PEG則會讓薄膜表面的孔洞變大，進而降低截流率，另一方面，高分子量的PEG會導致海綿狀結構的厚度增加，而減少薄膜的透過率。 由於PEG在不同黏度的系統裡有截然不同的特性，在第三部分則會利用共溶劑，去探討不同黏度對過濾效能影響。沒有PEG的狀況下，膜的通量一開始隨著黏度上升而增加，但黏度過高時會導致海綿狀結構厚度過厚，而出現轉折點。在導入PEG的狀況下，高分子量PEG能有效提高低黏度薄膜的透過率，相反地，低分子量PEG則在高黏度系統有較高的透過率。 良好的薄膜必須要有高純水透過率、高截流率兩項特點。而依據以上三個階段的實驗，可得知理想的巨颯薄膜結構必須滿足下列三點：較小的表面孔洞、高連通性的上層結構與低厚度的海綿狀結構。尋找高分子、溶劑與添加劑的最佳比例，為本研究最重要的目標之一。

In this study, we prepared polymeric solution with different kinds of solvent and additives to produce membranes with the wet immersion method of the non-solvent induced phase separation (NIPS). Afterwards, we discuss the structure of the membranes and their filtration performance. The polymer, polysulfone (PSF) was dissolved by DMAc with strong solubility and 2P with weak solubility, and poly ethylene glycol (PEG) was added as an additive. The experiments are divided into three parts: no additive system, additives system and co-solvent system. The first part is the no additive system. In PSF/DMAc system, the membrane structure is dense on the surface and there are many macrovoids on the cross-section. In PSF/2P system, the sponge structure appears on the upper cross-section, which results in high connectivity and contributes the higher permeability. The second part is to add PEG with different concentrations and molecular weights to two different solvent systems. From the rheological properties, it can be obtained that as the concentration and molecular weight of the additives increase, the viscosity of the casting solution also increases. In the PSF/DMAc/PEG system, the additive can effectively break through the walls between the macrovoids and increase the permeability of the membrane. As the molecular weight of the additive increases, this phenomenon is more significant. In the PSF/2P/PEG system , the additives will make the pore size on the surface of the membrane more larger, which reduces the retention of lysozyme. On the other hand, high molecular weight additives will increase the thickness of the sponge structure and reduce the permeability of the membrane. Because the additives influences are completely different in the different viscosities systems, in the third part, co-solvents will be used to research the influence of different viscosities on filtration performance. In the absence of additives, the permeability of the membrane initially when the viscosity increases, but as the viscosity is too high, the thickness of the sponge structure is too thick, and the permeability decreases. In the case of additives, high molecular weight additives can effectively increase the permeability in low viscosity systems. On the contrary, low molecular weight additives cause higher permeability in high viscosity systems. A good membrane must have two characteristics of high permeability and high retention. Based on the three parts of experiments, we can come to the conclusions that the ideal structure must satisfy the following three conditions: small surface pores, high connectivity between macrovoids in the upper layer, and low thickness of sponge structure. The most important goals of this study is to obtain the optimum ratio of polymer, solvent and additive.