Surfactants with Organosilicate Nanostructures for Use as Fire-Fighting Foams (F3)

Dr. Matthew Davis | NAWCWD China Lake

WP18-1519

Objective

The objective of this research project is to explore an innovative approach in using polyhedral oligomeric silsesquioxanes (POSS) as drop-in replacements of perfluoroalkyl surfactants found in current aqueous film forming foam (AFFF) concentrates used in fire-fighting by the Department of Defense (DoD). The new POSS surfactants produced in this research will contain only the elements carbon, silicon, hydrogen and oxygen. Foams containing the new surfactants will extinguish small-scale, unleaded gasoline pool fire in 45 seconds or less as dictated by MIL-F-24385F. In addition, the POSS surfactants will have low acute toxicity to fish and be biodegradable according to measurements of chemical oxygen demand and biological oxygen demand of microorganisms.

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Technical Approach

Commercially available alkylated POSS compounds will be chemically modified with hydrophilic polyethyleneglycol (PEG) units. A range of PEG lengths will be used in the selective modification to determine the proper size range imparting surfactant properties to the PEGylated POSS. By this approach, the organosilicate cage of the POSS surfactants will be targeted to reside at the airwater boundary layer of the bubble lamella in foams. The new POSS surfactants will be characterized by standard analytical techniques (nuclear magnetic resonance [NMR], gas chromatography mass spectrometry [GCMS]). Key physical properties of the POSS surfactants will be measured such as density, surface and interfacial tensions, foam expansion rate and spreadability. The POSS surfactants will be formulated into AFFF concentrates similar to commercial varieties used by the DoD. The thickness of POSS surfactant film, alone or in concentrate form, supported by hydrocarbon solvent will be measured. Small fire extinguishing experiments will be conducted to compare the differences (time to extinguish and burnback) between the POSS based AFFF and the current technology. The small-scale experiments will be a stepping stone to the large milspec test (MIL-F-24385F). A preliminary toxicity screening of the POSS surfactants by the Microtox assay and acute toxicity to fish will be made by fee-for-service laboratories.

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Benefits

This new technology could help the DoD eliminate perfluoroalkyl surfactants from AFFF concentrates since these compounds appear to be persistent in the environment. Eliminating perfluoroalkyl surfactant use could also mitigate future legal issues since it is not clear what their biological effects really are. Using nanomaterials such as POSS, it may be possible to extinguish fires with smaller quantities of chemicals than previous AFFF formulations.

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Points of Contact

Principal Investigator

Dr. Matthew Davis

NAWCWD China Lake

Phone: 760-939-0196

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