Exploring synergistic fire suppression of siloxane-glycoside firefighting foam using sulfonated hydrotrope additives to alter surfactant aggregation in solution

Abstract

Synergism between siloxane 502W and alkylpolyglycoside Glucopon 225DK surfactants in a mixture has resulted in a foam with firefighting potential. This synergism is not well understood, therefore additives were utilized to alter performance. Hydrotropes sodium benzene sulfonate and sodium p-toluene sulfonate were introduced to alter micelle size while keeping other solution properties constant and their effects were assessed for the individual surfactants and the mixture. Solution properties including micelle size (via dynamic light scattering) were measured along with the heptane vapor transport rate through a foam layer, foam expansion ratio, and fire extinction performance on a 19 cm heptane pool fire using a CO2 absorption measurement. Increased micelle size with hydrotrope addition did not directly correlate with improved fire suppression. Hydrotropes destabilized G225 aggregation, possibly due to G225 inter-surfactant hydrogen bonding potentials, which is limited for 502W. Hydrotropes inhibit the mixture G225 contribution while 502W remains. 502W is less effective individually, resulting in increased fire extinction times for the mixture with hydrotropes. Previously reported mixture synergism may be related to collaboration of individual surfactant contributions. Surfactant roles and inter-surfactant hydrogen bonding potentials are supported by the collected data, but have not been directly measured and require further evaluation.