The objective of this project is to demonstrate proof-of-concept for the development of the next generation of fluorine-free firefighting foam formulations as a replacement for existing aqueous film forming foam (AFFF). The novel foam systems produced in this research are derived from polysaccharide copolymers and nanoparticles that are sustainable, non-toxic, water-soluble (or water-dispersible) and will be applied using existing military firefighting equipment. These foam systems will meet or exceed both environmental regulations and firefighting performance defined in military specification (MIL-SPEC) MIL-F-24385F Military Specification: Fire Extinguishing Agent, Aqueous Film Forming Foam (AFFF) Liquid Concentrate, For Fresh and Seawater (1994).
The two routes for the non-fluorinated AFFF foams that will be explored are: (1) synthesis of hydrophobic modified chitosans as polymeric surfactants, and (2) surface modified chitosan nanoparticles for Pickering foams. Three different high-yield reactions will be employed to covalently link hydrophobic groups to chitosan via the amino groups: (a) amide coupling with fatty acids utilizing carbodiimde, (b) reaction with alkyl aldehydes (or ketones) followed by reducing the resulting Schiff bases, and (c) ring opening reaction of monoepoxidized fatty alcohols. Chitosan nanoparticles will be obtained by chemically modifying the amino groups on the surfaces by (a) carboxymethylation reaction, and (b) ring opening reaction of cyclic alkyl anhydrides. Both routes will be explored concurrently as a risk mitigation strategy to maximize resources and ensure success for this project at the same time.
The polymeric surfactants will be formulated with other hydrocarbon surfactants and other additives commonly used in manufacturing concentrated foam solutions. The key physical properties of the resulting foam candidates will be measured for their surface tensions in water and hydrocarbons, spreading coefficients (aqueous film formation), expansion ratio (fire extinguishment and burnback), and drain time (ability to cover fuel surfaces) as part of the optimization of foam formation research. Concurrently with the polymeric surfactant approach, Pickering foams will be formulated with or without other hydrocarbon surfactants and their key physical properties will be assessed by the same approach listed above. Each of the chemicals used and materials synthesized will be evaluated for their human health effects and environmental impact. Foam candidates will further be evaluated for their optimized concentrations. If the major objectives have been met, a small-scale fire extinguishment and burnback will be carried out.
The benefits to the Department of Defense (DoD) are multi-fold and include: a) elimination of the use of fluorosurfactants and related compounds in current AFFF foam formulations, b) elimination of legacy issues relating to environmental persistence and bioaccumulation, c) a significant reduction on the potential of ground water contamination and (d) the development of alternative AFFF formulation technology that enables long term sustained manufacturing using cost effective renewable resources. All of this will be achieved while ensuring mission readiness and firefighter safety.