Final Report: Fluorine-Free Hybrid Surfactants for Fire-Fighting FoamsEPA Contract Number: 68D02037
Title: Fluorine-Free Hybrid Surfactants for Fire-Fighting Foams
Investigators: Luebben, Silvia D.
Small Business: TDA Research Inc.
EPA Contact: Manager, SBIR Program
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Nanotechnology , Pollution Prevention/Sustainable Development , SBIR - Nanotechnology , Small Business Innovation Research (SBIR)
Aqueous film-forming foams (AFFFs) are among the most popular fire-fighting foams used against fuel and oil fires because of their effectiveness and their ease of application. Unfortunately, recent studies have shown that one key ingredient of AFFFs, the fluorosurfactant perfluorooctyl sulfonate (PFOS), is toxic to aquatic life and is a persistent chemical that accumulates in the blood of humans and other animals. Thus, the production of PFOS was stopped in May 2000. Among the phased-out products are 44 fire-fighting foams and foam components. The fire-fighting industry currently is stocked with materials that have been phased out and that, sooner or later, need to be replaced. New fluorosurfactants have been introduced into the market since 2000, and used to formulate aqueous fire-fighting foam concentrates. The toxicity of the new fluorosurfactants and their persistence in the environment are not well established and still are under investigation. Their presence in the future market is unsure. Therefore, the fire-fighting industry has an urgent need for new, environmentally friendly foaming agents and foam stabilizers to replace fluorosurfactants in aqueous fire-fighting foams.
In this Phase I research project, TDA Research, Inc. (TDA) began developing novel fluorine-free foam stabilizers for fire-fighting foam concentrates. TDA demonstrated that these foam stabilizers are compatible with current fire-fighting equipment and can be used to suppress fuel fires. TDA also identified new surfactant types that, in combination with TDA's foam stabilizers, offer the potential to make effective fluorine-free AFFFs.
During the project, TDA developed methods to reproducibly generate foam in a laboratory setting and prepared aqueous solutions containing TDA's proprietary foam stabilizers. These formulations also contain either a commercial fluorine-free surfactant or an in-house prepared fluorine-free low surface tension surfactant. The tendency of these aqueous solutions to foam and the stability of the foams to drainage were evaluated. First, several foam stabilizers were prepared and tested for their effects on foaming tendency and foam stability in combination with the surfactant sodium dodecyl sulfate. The most effective foam stabilizer candidate then was formulated into foam concentrates with various commercial surfactants.
Both the foaming tendency of the concentrates and the stability of the foam produced were compared to a commercially available AFFF concentrate. In these tests, TDA's formulations maintained a foaming tendency comparable with the commercial product and exhibited exceptional foam stability. The drainage rate of TDA's foams was up to 60 times slower than the drainage rate of the commercial AFFF. This could be a significant advantage in fighting large fires because a foam-covered area would not need to be re-foamed as frequently.
Several of the initial experimental foam concentrates exhibited very high viscosity, which would make them difficult to pump with current fire-fighting equipment. However, TDA recently found a means to decrease the viscosity of surfactant/stabilizer mixtures to a level that is acceptable for commercial foam-generating hardware. Thus, a 5-gallon sample of a low-viscosity foam concentrate containing a traditional nonfluorinated surfactant and TDA's foam stabilizers was prepared and shipped to a fire-testing laboratory, where it was tested by professional fire fighters against a large-scale alkane fuel fire. This test demonstrated that TDA's experimental concentrate generates a foam using standard fire-fighting equipment and that this foam can be used to extinguish hydrocarbon fires. The performance of this first formulation was not as good as the current fluorinated AFFFs. However, the fire-testing personnel thought that its performance was remarkable for a formulation undergoing its first large-scale test, because development of a new formulation usually requires more than 100 of these tests. The primary shortcoming of TDA's foam was that its film-forming properties were not sufficient and will need improvement.
To improve the film-forming properties of the formulation, TDA began to synthesize new fluorine-free low-surface tension surfactants at the end of this 6-month project. These new materials were incorporated in the experimental concentrate. The surface energetics, foaming tendency, and foam stability of the aqueous solutions obtained by diluting these modified concentrates were tested. Measurements showed that these modified solutions have lower surface tensions and good foaming tendencies and foam stability. The surface tension of the foam and the interfacial tension of the foam with the fuel determine whether the foam will spontaneously spread over the fuel, forming a thin aqueous film that helps advance the front of the foam against the fire and prevents backbiting of the burning fire. Unfortunately, due to time and budget limitations, TDA was unable to prepare sufficient quantities of these surfactants for a second full-scale fire test.
During the course of this project, TDA began to establish contacts with representatives of the fire-fighting industry. Many of them have expressed a concrete interest in this research and the promising preliminary results.