Sodium bentonite-based coatings containing starch for protecting structures in wildfire emergency situations

Coating materials were developed as a means of protecting structures from fires in emergency situations. Sodium bentonite (SB) gel and foam coatings were evaluated in burn tests for their ability to protect a sample of commercial lap siding from intense heat (42 kW/m2). Starch was added to some treatments to determine whether it stabilized the coating and prevented vertical slumping. A commercial fire protection gel coating was included in the study for comparison. Coatings containing starch and the SB gel sample had negligible slumping during burn tests while the commercial gel and the SB foam slumped severely during the test. In rheology studies, samples containing starch had higher G′ (elastic modulus), G″ (viscous modulus), and higher yield stress than the commercial gel or SB samples without starch. Surprisingly, the samples containing starch heated more slowly than samples without starch. This could be explained, in part, by the continuous boundary layer (crust) that formed during the burn test that shielded the substrate surface from direct heat exposure, minimized the exposed surface area, and, initially, lowered water vapor flux. Drying tests were performed at 44 °C to determine how long the coatings could remain hydrated under severe conditions. The SB gel coatings remained hydrated longer than the SB foam samples. Starch prolonged the drying time (reduced evaporation rate) for both the SB foam and gel samples.

Graphical AbstractFigure optionsDownload as PowerPoint slideHighlights
► Fire protective coatings containing sodium bentonite and starch were evaluated in burn tests.
► Starch improved the effectiveness of coatings in suppressing high temperatures.
► Starch helped stabilize the coatings on vertical surfaces and reduced slumping.
► Starch helped form a continuous surface skin that reduced the rate of drying.
► Starch formed a char residue that shielded the substrate from direct heat exposure.