Polyaniline and its derivative hollow fiber membranes for gas separation

• Main Author: Hasbullah, Hasrinah Binti
• Format: Dissertation
• Language: English
• Published: Imperial College London 2012
• DOI: 10.25560/10117

This thesis describes research into the utilization of conducting polymer polyaniline (PAni) as a material for the development of asymmetric hollow fiber membranes for gas separations. In order to ensure the consistency of the emeraldine base PAni molecular weight and the quality and purity throughout this research, the fresh batch polymer was synthesized in-house prior to each hollow fiber spinning. The initial gas permeation test revealed that the hollow fiber fabricated with high molecular weight PAni was favourable due to the highly viscous solution prepared with significant polymer chain entanglement that contributed to the formation of a more desirable membrane structure. However, the major turn around of the work was the introduction of volatile tetrahydrofuran (THF) to less volatile N-methyl-2-pyrrolidone (NMP) in the dope solution that promoted a proper formation of integrally skinned membranes. The effective removal of THF at a high spinning air gap further improved the fabricated membrane morphology which consisted of a denser effective skin layer, transition layer and finely porous substructure with smaller macrovoids. In addition, the spine line stress-induced orientation at a high air gap was responsible for further stretching the nascent fiber creating more packed structure that assisted toward improving the gas separation performance of the membranes. The induced molecular orientation also resulted in improvement in mechanical properties of the hollow fibers. Polyaniline derivative was synthesized to overcome the PAni solubility issue and to suppress the formation of PAni micro-agglomerates in the highly viscous dope solution. Integrallyskinned hollow fiber membranes were successfully prepared by dry-jet wet spinning from poly(ortho-anisidine) (POAn) dissolved in NMP and THF system. The bulky methoxy group introduced to the polymer backbone increased both the polymer chain rigidity and specific free volume of POAn as compared to PAni, producing membranes with significantly enhanced gas pair separation factors and small gases (hydrogen and carbon dioxide) permeation rates. The final focus of this study was investigating the potential effect of the aging process on PAni and its derivative membranes gas separation and mechanical properties. Poly(o-anisidine) membrane properties were found to be more stable than polyaniline membranes throughout the aging period, providing a strong foundation for further investigation of poly(o-anisidine) as a membrane material for gas separation towards commercial application.