聚碳酸酯薄膜微結構之改變對二氧化碳氣體透過行為之影響

Effect of the micro-structure variation on carbon dioxide permeation behavior of PC membrane

劉勝文(Sheng-Wen Liu)

指導教授 ： ARRAY(0xc17f560)

中原大學/工學院/化學工程研究所/碩士(2009年)

https://doi.org/10.6840/cycu200901082

摘要

本研究以乾式相轉換法製備出緻密的聚碳酸酯（Polycarbonate，PC）氣體分離膜，再經由不同溫度進行熱處理，研究中主要藉由正子湮滅光譜（Positron Annihilation Spectroscopy，PAS）分析技術探討PC薄膜經熱處理後的物理結構變化及不同氣體環境下對氣體透過效能與塑化效應之影響。
藉由SEM、FTIR、DSC及UMTM測試發現，PC緻密薄膜經由不同溫度熱處理後，其表面型態結構、玻璃轉移溫度（Glass transition temperature，Tg）及機械性質並未有明顯地差異，但卻呈現不同的氣體透過效能，可見薄膜內仍有微結構變化是無法從傳統儀器觀察，因此本研究利用「正子湮滅光譜分析技術」，以分子的尺度觀察PC高分子薄膜經熱處理後，在不同氣體環境下膜內自由體積的變化。實驗中發現在常壓時，不管是否經過熱處理，薄膜內的自由體積分佈均呈現單一分佈，但經由二氧化碳加壓後，於一般o-Ps lifetime量測範圍(1~5 ns)會呈現雙孔洞分佈，因此定義o-Ps lifetime小於1.7 ns的範圍稱為小孔洞(τ3,small)及而大於1.7 ns的範圍稱為大孔洞(τ3,big)；但於惰性氣體氦氣的加壓環境下，隨著壓力增加，其自由體積並無明顯變化，故推測此現象為二氧化碳之塑化效應所導致。藉由氣體透過效能及正子湮滅光譜數據分析比較，經二氧化碳加壓後之PC薄膜，其氣體透過行為是以大孔洞(τ3,big)為主導。
從實驗結果中也發現PC薄膜於較多殘餘溶劑含量下，會呈現較明顯的塑化現象且在高壓下有較大的自由體積，但是經由高於Tg熱處理後，PC薄膜內殘餘溶劑含量的減少，使得塑化效應降低，隨著壓力增加則以壓縮效應為主導，並使得二氧化碳透過係數明顯下降。

關鍵字

熱處理 ； 塑化效應 ； 自由體積 ； 正子湮滅光譜分析技術 ； 氣體透過

並列摘要

In this study, dense homogeneous polycarbonate (PC) membranes were prepared via a dry-phase inversion method at different heat treatments and were tested for pure gas permeability of carbon dioxide (CO2). The effect of different gas pressure conditions as well as different heat treatments on the morphologies of dense PC membranes and on their gas permeability performances was studied with the use of positron annihilation spectroscopy (PAS).
There was no noticeable effect on the surface morphologies, chemical structures, glass transition temperatures (Tg), and mechanical properties of the different heat-treated PC membranes, as shown by the SEM, FTIR, DSC, and UMTM data, respectively. However, these heat-treated PC membranes had different gas permeability performances, so we could not characterize the change in their structure at the molecular scale by conventional instruments. The PAS was utilized to detect the free-volume size and the intensity of the heat-treated PC membranes at different gas pressure conditions. The free-volume in the PC membranes has monomodal distribution at atmospheric pressure environment, whereas bimodal free-volume distributions were attained at carbon dioxide pressure environment. The plasticization of carbon dioxide may lead to this phenomenon because there was almost no change in the free-volume size of the PC membranes with increasing pressure at inert gas (helium, He) pressure environment. Based on the analysis of the PAS data in regard to gas permeability performances, it seemed that big pores predominantly controlled the carbon dioxide permeation behavior.
The results showed that the free-volume and the gas permeability of the PC membranes increased with increasing amounts of residual solvent at high carbon dioxide pressure. For the PC membranes with low residual solvent contents above Tg, the gas permeability performance could be affected significantly by antiplasticization, and the free-volume and the gas permeability of the PC membranes decreased with increasing carbon dioxide pressure because the compression effect was predominant.

並列關鍵字

plasticization ； free-volume ； gas permeability ； Positron Annihilation Spectroscopy (PAS) ； heat-treated

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