Aqueous film-forming foams (AFFF) containing perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have been used for the past 5-6 decades by the Department of Defense (DoD) in fuel fire suppression operations. These chemicals have the strongest chemical bonds and are considered as persistent, bio-accumulative, and toxic substances. PFOA/PFOS chemicals have been detected around the world in the food chain, drinking water, animals, and even in human blood. Therefore, the Environmental Protection Agency has regulated the chemical industry for the complete elimination of PFOA and PFOS chemicals along with certain C6 substances (containing six fluorinated carbons) by 2015. Therefore, the DoD is seeking non-toxic PFAS-free alternatives to replace PFOA/PFOS in firefighting foam formulations.
In this project, specifically, functionalized siloxane-based surfactants were synthesized, and their chemical stability, physical properties, and fire suppression abilities were evaluated. The tests included benchtop testing, 28-ft² fire performance, spreading coefficient, and aquatic toxicity of the foam formulations.
A number of trisiloxane surfactants have been synthesized and successfully tested for their fire fighting capabilities, to enable the spontaneous formation of a water film on top of the fuel. The additives play a critical role in the extinction of fire and stability in water. The performance of trisiloxane surfactants are encouraging and have the potential to replace fluorine-containing AFFF. Further optimization of additive formulations are expected yield a PFAS-free formulation that can replace current AFFF.
PFAS-free formulations developed in this effort have potential as "drop-in" replacement for AFFF products and can meet the performance specifications of the fire extinguishing agent, based on MIL-PRF-24385F standard with further optimization of the formulations. The formulations are expected to be capable of complying with environmental regulations and to be safe for use by military personnel.