Polyimides epitomize one of the most versatile high-performance engineering polymers. Polyimides are inherently mechanically robust, chemically inert, and thermooxidatively stable to 400+ °C depending on their chemical structure, enabling their function in numerous aerospace, electronic, medical, and flame-retardant applications. Polyimides can be highly modular even within synthetic limitations, which promotes and sustains innovative research. One recent interest concerns the innovation of fire suppression foams. Aqueous film-forming foams (AFFFs) are regularly sought when engaging liquid fuel (gasoline, jet fuel) fires. AFFFs utilize perfluorinated compounds (PFCs) like perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), which exhibit toxicity, bioaccumulation, and persistence in the environment resulting in the presence of fluorosurfactant chemicals in environments either through direct or secondary exposure via chemical migration. Recently, the USEPA has even detected PFAS in drinking water at hundreds of military training facilities and civilian airports. While fluorinated compounds provide desirable thermooxidative stability and excellent fire retardancy, the environmental impact imposed by these chemicals strongly encourages research that targets the complete removal of PFCs in conventional formulations. This thesis focuses on the fundamental development of water-soluble sulfonated polyimide (sPI) and poly(amic acid) (sPAA) systems for next-generation polymer-based fire suppression foams. The use of sulfonated monomers and poly(amic acid) salt formation enables tunable structures and water solubilities. The polymers maintain competitive thermal stabilities to conventional polyimides and, when combined with readily available, non-toxic surfactants (SDS), produce stable foams. The MIL-F-24385F performance requirement evaluates foam quality/stability, drainage time, and burnback resistance to access viability and provides comparison to other systems; preliminary testing shows that sPI/sPAA formulations perform well. Solution rheology offers insights into fundamental scaling relationships of specific viscosity vs. concentration in both salt and salt-free solution that are important to future foam development. Additionally, the structural nature of the sPIs/ sPAAs allows for their modification with phosphonium moieties or siloxanes, which are slated to have positive effects on performance. Overall, these sPIs and sPAAs provide a promising platform for the future direction of fire suppression foams. / Master of Science / High-performance polymers are used in the most demanding of engineering applications. Polyimides represent one of the most versatile high-performance polymers. Polyimides are mechanically strong, chemically inert, and resistant to extreme temperatures depending on their chemical structure, allowing their use in numerous aerospace, electronic, medical, and flame-retardant applications. Polyimides are synthetically versatile, which enables the discovery of new uses after decades of research. One new targeted application is fire suppression foams. Aqueous film-forming foams (AFFFs) are the standard when battling liquid fuel (gasoline, jet fuel) fires. AFFFs contain perfluorinated compounds (PFCs), which are toxic and persist in the environment; they migrate easily to affect indirectly exposed ecosystems. Recently, the USEPA has even detected PFAS in drinking water at hundreds of military training facilities and civilian airports. While AFFFs with PFCs are highly effective, replacement materials are needed. This thesis focuses on the fundamental development of water-soluble sulfonated polyimide (sPI) and poly(amic acid) (sPAA) systems for fire suppression foams. The polymers remain thermally stable, and when combined with readily available surfactants (SDS), produce stable foams. Preliminary fire testing shows that sPI/sPAA formulations perform well against military specifications. Solution rheology (study of flow) explores the solution behavior of sPI, which offers insights into fundamental concentration-viscosity relationships that are important to future foam development. Additionally, the structural nature of the sPIs/ sPAAs allows for their modification with phosphonium groups or siloxanes, which changes their characteristics. Overall, these sPIs and sPAAs are initially promising for the future direction of fire suppression foams.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/103613 |
| Date | 28 May 2021 |
| Creators | Stovall, Benjamin Joseph |
| Contributors | Chemistry, Long, Timothy E., Deck, Paul A., Moore, Robert Bowen |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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