The objective of this project is to improve the performance of leading PFAS-free foams by adding functional additives, including PNS Syrup or novel, chemically related self-intumescent foaming agents (PNS-F). The project team will test the hypothesis that these additives will improve the stability of per- and polyfluoroalkyl substances-free foam bubbles by increasing the resistance to expansion and degradation. Ultimately the objective is to develop a PFAS-free foam formulation that can pass MILSPEC testing.
I) PNS will be added to commercialized PFAS-free foams and the performance will be evaluated. PNS is a fire extinguishing agent that is self-intumescent and forms a light-weight foamy char which stops the chain reaction of free radicals and ions in a flame and associated heat release. This is expected to decrease fire extinguishing time and improve foam bubble stability in FF foams. As PNS is not a foaming agent, extra surfactant or other additives may have to be added to optimize the formulation.
II) Ideally the surfactants and or foaming agents in PFAS-free foams could play a dual role, providing both foaming and insulation as well as directly participating in the fire extinguishing properties of the foam. Recently, the project team has succeeded in producing new foaming agents which are chemically related to PNS and possess foaming properties as well as self-intumescence to enable flame retardancy. As a group the project team refers to this family of compounds PNS-F. Currently the project team has made three related versions of PNS-F: PNS-F1, diethylenetriamine (DETA) lauryl phosphate ester, PNS-F2, DETA- ethoxylated tridecanol phosphate ester, and PNS-F3 DETA- ethoxylated tridecanol polyphosphate ester. As the project progresses, there will be other PNS-F formulations. The project team will characterize the foaming and fire retardant properties of these agents and use them alone or in combination with other agents to form a new PFAS-free foam. They will also investigate these agents as additives to existing commercialized PFAS-free.
III) One of the difficulties in developing new PFAS-free foam is that it is difficult to characterize the fire extinguishing ability of these foams without doing costly large scale, 28ft2, testing. Standard tests for evaluating flame retarded polymers are thermogravimetric analysis and cone calorimetry. Cone calorimetry will be used to measure ignition time, heat release rate, mass loss, and other fire characteristics of concentrates of aqueous film forming foam (AFFF), worst and best performing PFAS free foam, PNS/sodium laural sulfate, and PNS-F. The project team will determine whether this information is predictive of large scale fire performance.
IV) In previous work the project team applied the flame retardants as a mist to improve spreading and allow more interaction between the fire extinguishing agent with the reactive particles in the flames. The project team will quantify performance when the agents are applied as a mist or a conventional single stream. The goal will be to produce a foam that can be applied with existing equipment or equipment that can be easily modified.
PFAS-free foams are effective fire extinguishing agents which are approaching the capability of AFFF, but do not pass the MILSPEC test for class B agents. The project team suggests that PFAS-free foams have two main categories of limitations compared to AFFF. 1) The bubbles of PFAS-free foams are not as stable when subjected to high heat. This leads to bubble expansion and breakage before they can form a stable cover which seals the underlying flammable liquid. This project plans to improve bubble stability by introducing additives which have intrinsic fire extinguishing ability, meaning that the additive can directly interact with the free radicals and ions which perpetuate a fire. 2) The spreading coefficient of PFAS-free foams is inferior to that of AFFF. The project team will compare misting and single stream application techniques to assess how this impacts the spreading and performance of the foam. Adding these functional additives and/or using a new spray technique can boost the performance of PFAS-free foams so that they can pass MILSPEC and be more environmentally friendly.