聚醚碸薄膜中巨型孔洞生成機制之探討

Study on the macrovoid formation of Poly(ether sulfone) membranes

賴奕伶(Yi-Ling Lai)

指導教授 ： 王大銘

國立臺灣大學/工學院/化學工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02480

摘要

本研究係以非溶劑誘導式相分離法(Nonsolvent- induced phase separarion, NIPS)(又稱濕式法, Wet inversion process)來製備非結晶性高分子聚醚碸(Polyether sulfone，PES)薄膜，所使用的溶劑為N-甲基吡咯酮(N-methyl pyrrolidinone, NMP)以及2-吡咯烷酮(2-Pyrrolidinone, 2P)，研究中發現使用此兩種不同的溶劑，所生成的薄膜結構大相逕庭，薄膜結構中所生成的巨型孔洞(macrovoid)型態也有所不同。

　　以NMP為溶劑配製而成的鑄膜液，在經過濕式法成膜後薄膜主體為蜂窩狀結構(cellular structure)，巨型孔洞則從皮層以下開始成長。而以2P為溶劑配製而成的鑄膜液，成膜後的薄膜主體卻為雙連續結構(bicontineous)，且巨型孔洞是與界面有一段距離才開始生長。雙連續結構通常出現在不易成核成長的系統中，由於2P對於PES高分子而言為一不好的溶劑(poor solvent)，使得高分子鏈之間有更多的重疊交錯(entanglement)，增加了組成成核的阻力，因此在相分離後需要較長的時間成核成長。

　　第一部分我們嘗試調整高分子PES的濃度，希望增加鑄膜液的黏度用以增加成核的阻力，但從實驗結果發現，黏度增加雖然能夠成功的使巨型孔洞生成的位置加深、巨型孔洞長度減短，但在PES/NMP系統中僅有在皮層下出現一層薄薄的雙連續結構，薄膜整體依然為蜂窩狀結構。因此在第二部分嘗試在鑄膜液中添加非溶劑水，實驗結果發現水的添加降低了高分子PES的溶解度，且相分離速度加快而提高了成核的困難度，造成即使在同黏度值之下，添加的水越多對於巨型孔洞的起始位置與長度都有抑制的效果。薄膜整體結構上加入水的變化，與增加濃度的變化相同，PES/NMP系統仍舊以蜂窩狀結構為主。最後在第三部分嘗試在鑄膜液中添加兩種不同分子量的高分子聚乙二醇(Polyethylene glycol, PEG, 分子量為10000與20000)，由於PEG對高分子PES而言算是弱非溶劑， PES的溶解度下降且PES與PEG有更多分子間與分子內的糾結，同時也會加速系統相分離的速度，大幅提升系統成核成長的阻力。因此，當鑄膜液中添加10wt%以上的PEG，越多的PEG能夠使PES/NMP系統的結構趨向PES/2P的系統，薄膜的上半部皆以雙連續結構為主，且巨型孔洞的成長越接近膜底部。

關鍵字

聚醚碸濕式相轉換法 ； 非溶劑誘導式相分離 ； 巨型孔洞 ； 添加劑

並列摘要

In the present study, polyether sulfone (PES) membranes were prepared by nonsolvent- induced phase separarion (NIPS, also called wet inversion process) method and using N-methyl pyrrolidinone (NMP) and 2-Pyrrolidinone (2P) as the solvent. In the present work we found out that the morphology of the PES membranes prepared by these two different solvents were widely divergent, and the type of macrovoid formation in the PES membranes were also dissimilar.
As the casting solution was using NMP as the solvent, the PES membranes prepared by NIPS were mainly filled with cellular structure, and the macrovoid was form just beneath the skin layer. But as the casting solution was using 2P as the solvent, the PES membranes prepared by NIPS were mainly filled with bicontinuous structure, and the macrovoid was form under the skin with a little distance. In general, the bicontinuous structure occurs in the system which is not easy to nucleation and growth. Because 2P is a poor solvent to PES, poor solvent can cause the PES polymer chains to have more entanglements and increase the resistance to nucleation of the casting solution. For this reason, it need more time to nucleation and growth after the composition phase separation.
In the first part, increasing the polymer concentration in casting solution could increase the viscosity of the casting solution, and also increase the resistance to nucleation. Although increasing the viscosity could increase the macrovoid initiation position and decrease the macrovoid length successfully, but the morphology in PES/NMP system was still filled with cellular structure, only a thin layer of bicontinuous was beneath the skin layer. Therefore, in second part we tried to use water as a nonsolvent additive. Adding water can decrease the solubility of PES in solvent and speed up the phase separation rate, lead to increase the entanglement of polymer chains and the hard to nucleation. As the result, even under the same viscosity, the more water additive made the higher macrovoid initiation position and the lower length. But the morphology of the membranes with adding water had no obvious difference between the membranes altered by concentration, PES/NMP system was still filled with cellular structure. Hence, in the third part, we used two different molecular weight of polyethylene glycol (PEG, Mw=10000 and 20000) as additive. PEG is a kind of weak nonsolvent to PES , the solubility of PES will decrease and result in the inter- and intra-molecular aggregations and entanglements of the polymer chains in the casting solution. Also, adding PEG will made the casting solution more thermodynamics unstable, the phase separation rate will increase, it will large increase the nucleation resistance. Consequently, when the concentration of PEG was over 10wt% in casting solution, the more PEG additive could make the morphology of PES/NMP system was more likely to PES/2P system, over half upper part is filled with bicontinuous structure and the macrovoid is more closely to the membrane bottom.

並列關鍵字

polyether sulfone (PES) ； nonsolvent- induced phase separarion (NIPS) ； wet inversion process ； macrovoid ； additive

參考文獻

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