自由體積及氣體-高分子交互作用對高分子薄膜氣體吸附與傳輸性質之影響

Effect of free volume and penetrant-polymer interaction on gas sorption and transport properties of polymeric membrane

胡蒨傑(Chien-Chieh Hu)

指導教授 ： 賴君義 ； 阮若屈

中原大學/工學院/化學工程研究所/博士(2004年)

https://doi.org/10.6840/cycu200400190

摘要

摘 要
自由體積與氣體-高分子交互作用是決定高分子薄膜氣體分離性能最重要的參數，欲開發高性能氣體分離薄膜必須釐清自由體積、氣體-高分子交互作用與高分子薄膜氣體分離性能之相互關係，因此本論文首先探究鑄膜用溶劑、熱處理、高分子組成對玻璃態高分子薄膜自由體積、氣體吸附與傳輸性質之影響，接著探究氣體-高分子交互作用對薄膜氣體吸附與傳輸性質之影響，最後則討論在自由體積相同下薄膜表面交聯對薄膜氣體透過之影響。
鑄膜溶劑性質對同材質緻密PMMA薄膜FFV、玻璃轉移溫度、氣體透過係數與擴散係數之影響是本研究的重心，鑄膜使用之溶劑沸點較高則所製備薄膜玻璃轉移溫度較低但FFV較大，薄膜氣體透過係數隨著FFV增加大幅增高，固定PMMA使用不同溶劑製備薄膜的氣體透過係數最大相差近六倍，薄膜氣體透過係數增加與薄膜FFV增加趨勢一致，薄膜自由體積增加主要改變薄膜氣體擴散係數，而對氣體吸附影響不大。
鑄膜溶劑性質對高分子鏈堆疊的影響使薄膜有不同自由體積，一般認為在高於Tg溫度熱處理後，無論使用何種溶劑製膜相同膜材薄膜之FFV應該相似，本研究實驗結果證實經過熱處理之不同溶劑製備之薄膜的FFV明顯不同，熱處理提高薄膜之Tg同時降低PMMA薄膜之FFV。薄膜之氣體透過係數與溶解係數均因薄膜熱處理而下降，熱處理PMMA薄膜的FFV越高氣體透過係數越大，由於分子鏈局部塑化造成氣體壓力大於15 atm時薄膜的氣體透過係數有隨壓力增加而增大的現象，分子鏈局部塑化對薄膜氣體擴散係數的影響並不大。
除了鑄膜用溶劑及熱處理會影響高分子薄膜之氣體分離行為外，高分子之組成亦是影響薄膜氣體分離行為的重要參數，與氣體交互作用很小的norbornene含量不同使COC有不同分子結構，本研究使用組成不同COC薄膜探討氣體交互作用相似時分子組成對薄膜FFV、氣體吸附與傳輸性質之影響，COC薄膜中norbornene含量增加薄膜之密度降低但是玻璃轉移溫度與FFV提高，分子組成不同造成薄膜之FFV增加配合適當的分子鏈堆疊可同時提昇薄膜的氣體透過係數與選擇係數，COC薄膜之氣體溶解係數隨氣體操作壓力增高而下降(符合dual mode sorption之行為)，FFV越高之薄膜氣體吸附量越大，薄膜之FFV與C’H呈線性關係。
為了釐清氣體-高分子交互作用與薄膜氣體透過性質之關係，carbonyl group density不同的緻密薄膜被系統性探討，高分子之carbonyl group density增高會增加薄膜氣體溶解係數，carbonyl group與氣體分子之交互作用會抑制氣體分子在薄膜中的擴散。carbonyl group density與Langmuir affinity constant呈正比線性關係。
為探討薄膜自由體積不改變之情況下，薄膜表面交聯對薄膜氣體氣體透過性質之影響，本研究引用電漿進行薄膜表面交聯處理，薄膜表面交聯降低薄膜氣體透過係數但是增加薄膜氣體選擇係數，研究中亦發現薄膜表面交聯可改善薄膜抵抗冷凝性氣體塑化的性能。
鑄膜用溶劑、熱處理、高分子組成，官能基、薄膜表面交聯對高分子薄膜氣體分離性質均有顯著影響，本研究針對這些影響因子所做基本探討，有助於更清楚釐清高分子薄膜氣體分離機制。

關鍵字

溶解係數 ； 高分子薄膜 ； 擴散係數 ； 自由體積

並列摘要

Abstract
Free volume and penetrant-polymer interaction were important parameters to control gas separation properties of the membrane. To develop high performance gas separation membranes, the free volume and penetrant-polymer interaction dependence of gas separation properties of the membrane need to be established. Initially, effects of casting solvent, heat treatment, and polymer composition on free volume, gas sorption, and transport properties of glassy polymeric membranes were estimated in this thesis. Subsequently, the relationship between penetrant-polymer interaction and gas separation properties of membrane was investigated. This study finally reports the effect of surface crosslinking of membrane, same FFV, on gas permeation of polymeric membrane.
This work reports glass transport temperature, fractional free volume (FFV), permeability, and diffusivity of Poly(methyl methacrylate) (PMMA) membranes, yielding information regarding the effect of casting solvent property on transport mechanisms in PMMA membranes cast from five different solvents. It was found that the free volumes of the membranes followed the order of the boiling points of the solvents from which they were cast. Nevertheless, the trend of Tg was very opposite of FFV. An increase in FFV increased the gas permeability but apparently did not increase the gas solubility. The results indicated that the gas diffusivity in the membrane was strongly affected by the fractional free volume of the membrane.
Membranes with different free volume result from polymer chain packing caused by casting solvent properties. It was believed that annealing above the Tg of membrane made membranes prepared by dry casting from different solvents had similar FFV. In fact, the FFV of annealed membranes prepared by casting from different solvents still had obviously difference. Annealing increased the Tg of membrane but decreased the FFV of membrane. The annealing of membrane was discovered to simultaneously decrease both permeability and solubility. Penetrant permeability in annealed membrane increase with increasing FFV. The plasticizing effect of CO2 on PMMA is well known, but we found that the permeability of oxygen also increased slightly with the operating upstream pressure. The solubility of oxygen initially decreased and then soon increased with the upstream pressure. It was suspected that the increase of gas solubility by pressure was due to slight plasticization occurring in the edge of inter-chain aligning region near the self-coiling domain. The partial plasticization increased gas solubility and permeability but had little effect on the gas diffusivity.
Polymer composition was an important parameter affect gas separation properties of dense membrane besides casting solvent and heat treatment. Cyclic olefin copolymer (COC) containing 40-66mol% norbornene, small interaction with penetrant, had different structure. The effect of molecular composition change of COC membrane on FFV, gas sorption, and transport properties was investigated in this work. Glass transition temperature and FFV increase with increasing norbonene content, but we found that the density of membrane decrease with increasing norbonene content. COC membrane combines increasingly FFV with suitable chain packing simultaneously increase permeability and selectivity. The solubility of COC membranes increase with increasing FFV, and the gas sorption behavior of COC membrane obey the dual-sorption model. It is found that there is a linear relationship between FFV and Langmuir capacity constant.
The object of present work was to search for the relationships between the carbonyl group density and transport properties in the membrane. The intrinsic gas transport properties, permeation, diffusion, and sorption in a series of dense membranes with various carbonyl group densities were investigated. It was found that solubility is improved by increasing the carbonyl group density on the polymer chains of various polymers and this effect becomes more pronounced with increasing penetrant condensability. It was observed that the carbonyl group in the membrane decreased the gas diffusivity because it might have a strong interaction with the penetrant gas molecules. In this study, a direct relationship was found between the carbonyl group density and Langmuir affinity constant.
In this report, effect of surface crosslinking of membrane on gas permeation was studied from the viewpoint of FFV of membrane was not change. Argon plasma was used to create surface crosslinking of poly(methyl methacrylate) (PMMA) membrane. It was found that membrane surface crosslinking decreased permeability but increased selectivity. Additionally, the plasticizing effect of permeant (CO2) on the surface crosslinked PMMA membrane is significantly reduced.
The factors of casting solvent, heat treatment, polymer composition, functional group, and surface crosslinking obviously affect the gas separation performance of polymeric membrane. The basic study of effect upon above factors could help us to clarify the gas separation mechanism of polymeric membrane.

並列關鍵字

Polymeric membrane ； Diffusivity ； Solubility ； Free volume

參考文獻

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