Impact of humidity and polymer blending on the gas transport properties of polybenzimidazoles

dc.contributor.advisorFreeman, B. D. (Benny D.)
dc.contributor.advisorPaul, Donald R.
dc.contributor.committeeMemberSanchez, Isaac C
dc.contributor.committeeMemberRiffle, Judy S
dc.contributor.committeeMemberLynd, Nathaniel A
dc.creatorMoon, Joshua David
dc.creator.orcid0000-0002-4402-2362
dc.date.accessioned2019-12-21T00:56:04Z
dc.date.available2019-12-21T00:56:04Z
dc.date.created2019-08
dc.date.issued2019-07-17
dc.date.submittedAugust 2019
dc.date.updated2019-12-21T00:56:05Z
dc.description.abstractPolybenzimidazoles (PBIs) are attractive polymers for gas separation membranes due to their high chemical and thermal stability and rigid, size-selective molecular structures. Opportunities exist for using PBIs for high temperature H₂/CO₂ separation, among other separations, where significant amounts of water are often present. However, PBIs are uniquely hydrophilic glassy polymers, and the impact of humidity on PBI gas transport properties is not well understood. Highly sorbing penetrants like water are often considered to affect molecular transport in polymers through phenomena such as competitive sorption, antiplasticization, and plasticization, but greater fundamental understanding is needed to relate these phenomena to other key concepts in polymer transport like free volume. Additionally, opportunities exist to improve low PBI gas permeabilities through material modification. This study investigates fundamentals of water sorption, dilation, and diffusion in PBIs to develop a systematic understanding of how water uptake affects molecular transport in hydrophilic glassy polymers. Water vapor sorption and swelling in PBIs were experimentally measured, which enabled direct evaluation of polymer free volume changes arising from water uptake. Gas transport properties were measured across a range of humidities using a custom experimental apparatus and correlated with humidity-induced free volume changes. This analysis enabled unique insight into the tradeoff between competitive sorption, antiplasticization, and plasticization effects of water sorption on PBI transport properties. Similar analysis could be used to investigate fundamentals of mixed penetrant sorption and diffusion in other polymers. Finally, a method of improving PBI gas separation properties by blending PBIs with a more permeable polymer was investigated. Commercial PBI was blended with an ortho-functional polyimide capable of undergoing thermal rearrangement at high temperatures. Films of PBI blended with a small fraction of polyimide exhibited matrix-droplet morphologies that enabled synergistic combination of PBI and polyimide gas separation properties. Heat treatment caused thermal rearrangement of the polyimide phase, increasing blend H₂ permeabilities, while also increasing structural order in the PBI phase, increasing blend H₂/CO₂ selectivities. The net result of heat treatment was simultaneous improvement in both H₂ permeability and H₂/CO₂ selectivity at ambient temperatures, surpassing the 2008 H₂/CO₂ upper bound
dc.description.departmentChemical Engineering
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/2152/78819
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/5874
dc.language.isoen
dc.subjectGas separation
dc.subjectMembrane
dc.subjectPolybenzimidazole
dc.subjectPBI
dc.subjectHumidity
dc.subjectGas transport
dc.subjectPolymer
dc.subjectBlend
dc.subjectSorption
dc.subjectDiffusion
dc.subjectDilation
dc.subjectPermeability
dc.subjectFree volume
dc.subjectAntiplasticization
dc.subjectPlasticization
dc.subjectCompetitive sorption
dc.subjectPolyimide
dc.subjectThermally rearranged
dc.titleImpact of humidity and polymer blending on the gas transport properties of polybenzimidazoles
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentChemical Engineering
thesis.degree.disciplineChemical Engineering
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy
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