This dissertation focuses on the synthesis and characterization of high performance polymers, specifically polybenzimidazoles (PBIs) for gas separation applications and polyimides (PI) for water purification and as interfacial agents for thermoplastic carbon fiber composites.
Two methods for improving the gas transport properties (for H2/CO2 separation) of a tetraaminodiphenylsulfone (TADPS)-based polybenzimidazole were investigated. Low molecular weight poly(propylene carbonate) (PPC) and poly(ethylene oxide) (PEO) were incorporated as sacrificial additives that could be removed via a controlled heat treatment protocol. PBI films containing 7 and 11 wt% PPC (blend) and 13 wt% PEO (graft) were fabricated and the gas transport properties and mechanical properties after heat treatment were measured and compared to the PBI homopolymer. After heat treatment, the 7 wt% PPC blend exhibited the highest performance while retaining the toughness exhibited by the PBI homopolymer.
Novel sulfonated polyimides and their monomers were synthesized for use as interfacial agents and water purification membranes. Polyimides are high performance polymers that have high thermal, mechanical, and chemical stability. The objective was to assess structure-property relationships of novel sulfonated polyimides prepared by direct polymerization of the diamine monomers. A series of sulfonated polyimides was synthesized using an ester-acid polymerization method with varying degrees of sulfonation (20%, 30%, and 50% disulfonated and 50% and 100% monosulfonated polyimides). The results showed that the toughness of the polyimides in the fully hydrated state was much better than current commercial cation exchange membranes.
A 100% disulfonated polyimide (sPI) and poly(amic acid) salt (PAAS) using the same monomers used for the synthesis of Ultem® were utilized as suspending agents for the fabrication of coated sub-micron polyetherimide (PEI) particles. Sub-micron particles were obtained using 1 wt% PAAS and 4 wt% sPI to coat the PEI. The PEI particles were coupled onto ozone treated carbon fibers using a silane coupling agent. SEM images showed a significant amount of particle coating on the treated carbon fibers compared to the non-silane treated carbon fibers. / PHD / This dissertation describes synthetic and processing techniques used to fabricate materials for applications such as, water purification and gas separation. The polymers included in this dissertation include polybenzimidazoles and polyimides, which are materials that have exceptional mechanical and thermal properties. The polybenzimidazoles were specifically used for gas separation, while the polyimides were synthesized for use as water purification membranes and surfactants for coating polyimides and carbon fibers.
Gas separation membranes are effective tools for purifying gas mixtures (e.g. H₂/N₂, O₂/N₂, CO₂/CH₄). Additionally, they offer the advantage of being economical and environmentally-friendly compared to other methods of separation (e.g. cryogenic distillation). Many synthetic membranes made from polymers are used commercially, however, very few polymers can be used for elevated temperature separations. Because polybenzimidazoles exhibit high thermal stability, they are excellent candidates for high temperature gas separations (specifically H₂/CO₂ gas mixture). However, polybenzimidazoles have inherently low gas permeabilities. Thus, the focus of this research was to develop a simple method to introduce “pores” into the polymer membrane to improve gas permeability.
Water purification is a very important process as the demand for clean water increases with the growing global population. Currently, one-third of the global population experience water scarcity, and by 2025, two-thirds of the world’s population may face water shortages. Multi-stage flash distillation is the most widely used method for water desalination from sea water but it is also the most energy intensive process. Water desalination using polymer membranes (e.g. reverse osmosis, nanofiltration, electrodialysis) has been developed as low energy and environmentally-friendly alternatives for producing clean water. The current state-of-the-art membranes used for water purification lack mechanical integrity and chemical resistance, which complicate and reduce the overall efficiency of the separation process. Thus, the focus of the research was to synthesize polyimide membranes with improved toughness and chemical stability.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96219 |
| Date | 03 July 2018 |
| Creators | Joseph, Ronald Matthew |
| Contributors | Chemistry, Riffle, Judy S., Turner, S. Richard, Orler, Edward Bruce, Matson, John B., Frazier, Charles E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/vnd.openxmlformats-officedocument.wordprocessingml.document |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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