Fluorine-Free Extinguishing of a Hydrocarbon Pool Fire with a Suspension of Glass Bubbles Grafted with Nanoscale Polymer Layers.

The current most efficient solution to extinguish liquid hydrocarbon (class B) pool fires involves fire-fighting foams containing fluorinated surfactants. However, fluorocarbon surfactants are unsafe due to their environmental persistence and negative toxicological/bioaccumulative impact. To this end, we show that fluorine-free aqueous suspensions of Glass Bubbles (GB) modified with hydrophilic polymer grafted layers can efficiently extinguish hydrocarbon pool fires. Namely, GB grafted with poly(oligo (ethylene glycol) methyl ether methacrylate) (POEGMA), GB-G was fabricated employing "grafting-through" and "grafting-from" methods and used to obtain the suspensions. It was found that the GB suspension, with a grafted layer of higher molecular weight and lower grafting density (GB-GL), proved superior to the more densely grafted GB-GH and nongrafted GB-0 system. The GB-GL suspensions displayed less negative spreading coefficients and viscosities lower than those of GB-GH/GB-0 compositions. When siloxane-polyoxyethylene surfactant was added to all GB suspensions, the interfacial properties were dominated by the surfactant, with all suspensions having the same positive spreading coefficient. However, the GB-GL-surfactant composition had the lowest viscosity among the suspensions studied in this work. Specifically, the viscosity of GB-GH and GB-0 suspensions at a shear rate of 77 s -1 was ∼110% and 70% higher than that of GB-GL. Due to the lower viscosity, the GB-GL suspension demonstrated the most efficient spreading over model hydrocarbon solid (polyethylene) and liquid (hexadecane) surfaces when the surfactant was added. The suspension also showed the best performance in the retardation of hexane evaporation when placed over the heated hexane pool. After 50 min, the amount of hexane that evaporated through GB-GH and GB-0 suspensions was ∼8 and 11 times higher, respectively, compared to the GB-GL suspension. We found that the GB-GL-surfactant system was the most efficient GB suspension in extinguishing the fire due to its superior spreading and sealing ability. It was within 10% of fluorine-containing foam's fire extinguishment performance. The GB suspensions are much safer in terms of burnback resistance as a torch applied directly to the suspension after extinguishment could not reignite the fire. The GB material is recyclable, since it can be collected and reused after application to a fire.