添加劑對聚醚碸/聚碸薄膜結構與過濾效能的影響

Abstract

在製膜實務上，除了高分子、溶劑、非溶劑三成分外，常會加入添加劑以調整薄膜結構與分離效能，在添加量不多的情況下，濾膜結構與分離效能卻有很明顯的變化。此四成分的系統十分複雜，故文獻上對於添加劑所扮演之角色及其功能尚未有深入且全面的了解。本研究將聚醚碸、聚碸以DMAc及2P兩種溶解力不同的溶劑溶解，並加入不同濃度之PVP添加劑，以濕式法製膜，透過建立與分析系統釐清了添加劑對製膜參數、薄膜結構、過濾效能的影響。 加入PVP會使鑄膜液黏度提高，也會對薄膜結構之皮層厚度造成影響，皮層隨著添加量增加而增厚，但在低黏度與高黏度系統呈現不同的趨勢，在高黏度系統由於高分子鏈糾纏劇烈，系統穩定度升高至足以抵擋非溶劑直接流入，皮層增厚幅度大。此外，在低黏度系統，PVP可以發揮造孔劑的功能，增加薄膜連通性，讓純水透過率大幅提升，然而，在高黏度系統，皮層增厚帶來的阻力遠超越連通性變化的影響，純水透過率反而降低。根據蛋白質之截留率實驗結果，顯示添加PVP對於薄膜結構的影響主要在截面而非表面，仍維持優秀阻擋物質的能力。 綜合比較與評估各系統，本研究發現高純水透過率薄膜的製備是與孔洞連通性提升、皮層增厚的競爭關係高度相關，此準則可望適用於不同高分子/溶劑/添加劑系統，作為配方設計的參考。

In the practice of membrane fabrication, in addition to the basic three components which are polymer, solvent and non-solvent, additives are often added to modify the structure and separation efficiency of the membrane. Even only with small amount of addition, the membrane structure and separation efficiency can have obvious changes. The four-component-system is quite complex, so there are no thorough understandings of the functions of the additives and what role they play in the literature. In this study, polyethersulfone and polysulfone are dissolved in DMAc and 2P, which are two kinds of solvent with different solvency, and different concentrations of PVP are added to the system to fabricate membranes via wet immersion method. By establishing and analyzing the systems, we clarify the additive effects on casting conditions, membrane structure and filtration performance. The addition of PVP would make the casting solution viscosity higher and also affect the skin thickness of the membrane. The more PVP is added, the thicker the skin becomes. But there shows a different trend in the low viscosity system and the high viscosity system. Due to the strong entanglement of polymer chains in the high viscosity system, the stability of the system is high enough to resist the direct inflow of non-solvent, so the skin thickness increases significantly. Furthermore, PVP can play the role of pore-forming agent in the low viscosity system, which enhances the connectivity and boosts the water permeability. However, in the high viscosity system, the resistance caused by skin thickening far exceeds the positive effect on connectivity, which makes water permeability decrease. According to the experimental results of protein retention, it is shown that the influence of PVP addition on the structure of the membrane is mainly for the cross-section area rather than the top surface, which maintains the outstanding capability to block particles. After comparing and normalizing each system, our research finds that fabricating membrane of high permeability is highly related to the competitive relationship between pore connectivity enhancement and skin thickening. This principle is potentially applicable to different polymer/solvent/additive systems, as a reference for formulation design.