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Abstract: Fire-resistant fabrics used in protective clothing experience a reduction in performance because of ageing. Yet there are generally few visible clues before the loss in performance has reached a dangerous level. To solve this issue, a graphene-based end-of-life (EOL) sensor is being developed at the University of Alberta which will be placed as a patch on the protective clothing’s surface. It will indicate when fire-resistant fabric of the protective clothing has reached an unsafe level of performance. My thesis aims to identify the most suitable fabric to serve as a support for the EOL sensor. The support fabric should be flame resistant and washable. It should also withstand ageing conditions (e.g. temperature, ultraviolet light, and moisture) without degrading. Therefore, a series of FR fabrics made of different materials as well as those that are commonly used for fire protective clothing were subjected to accelerated ageing at specific conditions. The residual mechanical performance was assessed to identify the best candidate for the support fabric. The final candidate fabric was coated with reduced graphene oxide (rGO) so that the durability of the rGO coating to washing and the quality of bond between the coating and the selected support fabric could be assessed. This was done by monitoring changes in the surface conductivity of the rGO coating and observing changes in the morphology of the coating on the support fabric following multiple laundering cycles. The fabric substrate is the cornerstone for the development of the graphene-based EOL sensor. The success of the selected fabric substrate and meeting the requirements proposed will allow the manufacturing of the EOL sensor which will be suitable for keeping firefighters safe and ensure that their protective clothing is safe to use.

The promising potential of polybenzimidazole (PBI) membranes for high temperature (~200 °C), hydrogen-selective gas separations has been reported for many membrane geometries (e.g., bulk, composite, and hollow fiber), but never for sub-micron, spin-cast membranes. Numerous studies have shown that the performance of spin-cast membranes, which simulate commercially relevant thicknesses, declines more quickly with time than that of thick membranes due to accelerated physical aging. However, because most existing membranes are used near ambient temperature, the physical aging of sub-micron, spin-cast membranes has never been studied at temperatures above 55 °C. Because physical aging is dependent on both thickness and temperature, emerging high temperature membrane applications make it both intellectually and practically imperative to characterize spin-cast membranes in this new temperature regime. For the first time, physical aging studies of spin-cast, sub-micron membranes have been extended to elevated temperatures. PBI membranes, cast from commercial-grade Celazole®, were aged in a high-temperature permeation system while the gas permeabilities were periodically measured over more than 1500 hours. When aging at 190 °C, membrane gas permeabilities decreased rapidly then plateaued after 300 hours of aging. The observation of a plateau (i.e., equilibration) had never before been seen for a membrane, nor, to our knowledge, for any polymer ~250 °C below its glass transition temperature. Decreases in membrane permeability were accompanied by increases in selectivity for H₂, which are traditionally represented by Robeson upper bound plots. These shifts were consistent with previous membrane physical aging studies and indicate membrane size-sieving ability improves with aging. Celazole®’s permeability reductions at lower aging temperatures (e.g., 175 °C) were qualitatively similar to those at 190 °C, but occurred over a longer time period. When graphed vs. the logarithm of aging time, the permeability reductions at various temperatures could be superimposed via time-temperature superposition, which is a hallmark of physical aging. A thorough review of physical aging studies in the polymer physics literature is presented to give context for this unexpectedly short equilibration time far below the glass transition. Comparisons are then made between the current study and previous aging studies in the polymer physics field. Overall, the observation of a plateau at short aging times for a polymer deep in the glassy state casts doubt on our understanding of physical aging’s temperature-dependence and our ability to predict membranes’ long-term stability in elevated temperature applications.

Polybenzimidazoles (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

About 94 million tons of hydrogen is consumed annually as a chemical feedstock worldwide. Hydrogen is also a promising energy carrier. As both a chemical feedstock as well as a renewable energy carrier, very pure hydrogen is required. Electrochemical hydrogen pump cells operating at 120°C - 180°C with a polybenzimidazole membrane imbibed with phosphoric acid were investigated for the electrochemical purification and pressurization of hydrogen. In this device, dilute or impure hydrogen gas is oxidized at the anode, the proton product crosses the membrane to the cathode where they are reduced to form hydrogen gas. It was found that the pump cell could purify simulated reformate containing 3% CO. A cell voltage of 0.145 V, or 0.03 W/cm2, was required to operate the cell at 150°C and 0.2 A/cm2. This corresponds to 7.7 watt-hours per mole of hydrogen pumped which is 1,000 – 10,000 times smaller than conventional purification techniques such as pressure swing adsorption. It was also found that the electrochemical pump cells could purify and pressurize the simulated reformate to at least 20 psi above the inlet pressure with only one 50 cm2 lab prototype cell. With cell pressure differentials above 5 psi, there was an undetermined amount of hydrogen back diffusion across the membrane. The ability of the pump cell to operate continuously over 20 hours was also investigated. Operating at current densities above 0.4 A/cm2 resulted in a decrease in the membrane conductivity. The membrane conductivity could be recovered to some degree by reversing the electrodes (i.e. the anode became the cathode and vice versa). These effects are thought to be due to the phosphoric acid building up in the electrodes, reducing electrode performance and facilitating phosphoric acid loss from the membrane.

Much research has been conducted about project-based instruction (PBI) instantiation under a variety of conditions, yet there is a lack of literature that details the successes and challenges accrued by students, teachers, and outside observers during actual PBI implementation. In order to determine the conditions necessary to realize a successful project, I have developed a method (modified from Petrosino’s PBI research with preservice teachers [19]) to investigate the PBI affinity and knowledge level of participants. Students, teachers, and observers will complete a survey and rate a specific project experience from their past using a PBI literature-based project rubric; the rubric analyses will be compared to their survey responses as a further assessment of their philosophical support and comprehension of PBI. Furthermore, I have created three protocols to interview a random subset of participants from each frame of reference. I will then compare the responses of each group to responses from PBI researchers with expertise in the history and practice of PBI, illuminating precisely where PBI theorists and practitioners diverge. This data will allow us to analyze ways in which the interacting beliefs and actions of these three groups complicate the practical implementation of PBI. By identifying where PBI implementations struggle, we can suggest and construct successful scaffolds for students, teachers, and classroom observers.

Proton conducting membranes for a direct methanol fuel cell (DMFC) were prepared from the following polymer blends: Sulfonated poly[bis(phenoxy)phosphazene] (SPOP)– polybenzimidazole (PBI), Nafion – Teflon FEP (copolymer of Tetrafluoroethylene and hexafluoropropylene), and Nafion – PBI. Films were made by either solution casting (for SPOP-PBI and Nafion-PBI) or melt processing (for Nafion-FEP). The resulting membranes (50-120 ìm in thickness) were evaluated in terms of water swelling, proton conductivity, and methanol permeability. They were also fabricated in membrane electrode assemblies and tested in a DMFC at 60°C. The proton conductivity and methanol permeability of the membranes were found to be dependent on the blend composition, e.g., ion-exchange capacity of SPOP and wt% of PBI (for SPOP-PBI blends), wt% FEP (for Nafion-FEP), and Nafion protonation degree and wt% PBI (for Nafion-PBI blends). The DMFC performance (maximum power density) with a SPOP-PBI membrane was comparable to that of a Nafion 117 at 1.0 M methanol, but the methanol crossover flux was 2.6 times lower than that of Nafion 117. With blended Nafion-FEP and Nafion-PBI membranes, the current-density/voltage behavior in a DMFC was similar to Nafion, with 1.4 and 1.5 times lower methanol crossover. Significant cost savings can be realized when using the blended films rather than Nafion 117 because they are thinner than Nafion 117 (by a factor of 3.0-3.5) and contain less of the expensive perfluorosulfonic acid polymer. With increasing methanol concentration (up to 10.0 M), the blended membranes exhibited superior DMFC performance and lower methanol crossover fluxes as compared to Nafion 117.