There presently exists an extreme need for a replacement for the current aqueous film-forming foams (AFFFs), which utilize fluorinated surfactants. To this end, hollow glass microspheres (HGMs) stand out as potential components of a fluorine-free firefighting foam. They exhibit low thermal conductivity, low density, and their surface can be easily modified to tailor their behavior within an aqueous suspension. In this study, we used several polymer grafting methods to modify the surface of HGMs with hydrophilic polymers to tailor HGM surface properties and ultimately determine how the composition and graft density of polymers on the surface of HGMs influence the firefighting performance of HGM suspensions. Poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) with various polyethylene glycol side chain lengths was attached to the surface of the HGMs with a range of graft densities. The HGMs were first characterized using thermogravimetric analysis (TGA) to determine the amount of polymer grafted and scanning electron microscopy (SEM) to ensure homogenous surface modification. The molecular weight of each polymer was found through static light scattering (SLS) to determine the graft density on the surface of the HGMs. With the HGM suspensions, shear viscosity, surface tension, interfacial tension with hexadecane, and spreading on liquid and solid hydrocarbon surfaces were studied. Additionally, a fuel vapor flux test using an infrared gas sensor was performed with each HGM suspension. Finally, a benchtop fire extinguishment test was conducted with the HGM suspensions and demonstrated that HGM surface modification with hydrophilic polymers decreases the extinguishment time.

Fluorine-free hollow glass microsphere-based firefighting suspensions

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