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The objective of this project is to develop a per and poly fluorinated alkyl substance (PFAS)-free surfactant formulation that meets the performance requirements defined in MIL-F-24385F (Amendment 3), and is an environmentally friendly, drop-in replacement for the current environmentally hazardous Aqueous Film Forming Foam (AFFF).
In the project team's previous work, it was discovered that changes to surfactant’s chemical structure, surfactant-fuel interactions, and synergism between silicone and hydrocarbon surfactants could affect fire suppression significantly [34,36]. The project team showed that surfactant-fuel interactions and synergisms affect foam dynamics (foam spread on a burning fuel-pool surface, fuel permeation through foam layer covering the pool, and foam degradation), which are the key mechanisms by which an aqueous foam suppresses pool fires.
Systematically varying the chemical structures to suppress surfactant-fuel diffusion and to increase synergistic interactions between the surfactants will lead to enhanced fire suppression for heptane and gasoline fuels. The project team will synthesize silicone-oxyethylene surfactants with varying head and tail structures. They will vary inorganic and organic parts, size, polarizability, steric crowding of the tail groups, and polarity of the head groups. This will be achieved by changing conformation (linear, branched, cyclic) and with methyl, and ionic substituents. They will also use low viscosity, drop-in, solvents/additives as surfactant reinforcers to affect hydrogen bonding and micelles in solution.
The project team will quantify the effects of changes to the surfactant chemical structures on bubble coalescence rate at the foam-fuel interface, in addition to the foam dynamics and fire extinction for heptane and gasoline fuels at bench-scale. In addition to the aliphatic fuels like heptane, gasoline contains branched/cyclic/aromatic fuels, lubricants, and other additives that can affect PFAS-free foams’ fire suppression differently from heptane. The project team will also screen for acute lethality endpoints (LC50), chronic sublethal toxicity endpoints (EC50, IC50, probabilistic no effect concentrations), and the impacts of biodegradation on new surfactant formulations and toxicity. For leading surfactant candidates, the project team will also conduct 28 ft2 MilSpec pool fire extinction test.
A PFAS-free alternative to the current AFFF will eliminate the bio-accumulative, environmentally persistent, and toxic perfluoroalkyl surfactants and any derivatives. This will be achieved by eliminating the presence of extremely stable carbon-fluorine chemical bonds from the surfactant molecules in the firefighting foam. The PFAS-free firefighting foam will be an improvement over the telomere-based fluorosurfactant products, which still contain carbon-fluorine bonds to a varying degree. The PFAS-free firefighting foam will lead to lower projected risks to the aquatic environment and human health. While it is expected to be substantially less detrimental to the environment, to be a successful alternative to AFFF, it must maintain essential fire suppression performance critical to Department of Defense applications and should have low viscosity to be compatible with existing hardware for a drop-in replacement unlike existing commercial PFAS-free foams.