One strategy for limiting the damage and danger caused by building fires is to use flame-retardant coatings to protect construction materials. Some strategies for applying these coatings involve multiple steps and are not feasible for all manufacturers due to highly-porous materials like wood taking extended amounts of time to soak and dry during the treatment process. Additionally, some of the chemicals used for these treatments cannot be reused and bring about concerns of environmentally harmful waste. Researchers from Texas A&M University and the National Institute of Standards and Technology (NIST) recently presented research at the Spring 2022 meeting of the American Chemical Society describing a new environmentally-friendly coating that reduces the flammability of wooden materials while also reducing the time and costs of treatment.
The new method involves one step for dipping the wood in an aqueous solution containing the positively charged polymer polyethylenimine (PEI), the monomer hydroxyethyl methacrylate phosphate (HMP) and a photoinitiator called TPO, followed by just a few minutes of curing via ultraviolet light. The UV exposure causes TPO to convert HMP to a negatively charged polymer, which then forms a polyelectrolyte complex with PEI, imparting flame-retardant effects. The coating solution is less toxic and less environmentally harmful than other types of fire retardant treatments, and the resulting coating is transparent and just a few micrometers thick. Additionally, the ingredients for the solution are relatively low cost and widely available, according to the researchers.
Flammability testing in the laboratory showed that plywood treated with this coating quickly formed a layer of char on the surface, protecting the underlying wood and limiting damage and the fire spread. The coating also reduced smoke production by 56% compared to untreated plywood, according to co-investigator Thomas Kolibaba of NIST. The coating could be used for construction materials including wooden studs and framing as well as oriented strand board, and due to the method’s simplicity and the low toxicity of the coating ingredients, it could even be used by homeowners to protect existing structures using a backpack sprayer, Kolibaba added. Additionally, the same coating could be applied to other materials like textiles and polyurethane foam. In the future, the UV-curable polyelectrolytes could be developed into a resin to create flame-resistant 3D-printed parts, said Kolibaba.
“There’s a lot of concern about toxicity with flame retardancy,” said principal investigator Jaime Grunlan of Texas A&M University. “And here we’re providing an environmentally benign but equally or even more effective flame retardant treatment.”
The researchers are now working with industrial and government partners to further develop the coating and make it available to help produce safer construction materials.
Video Credit: American Chemical Society
Video Credit: American Chemical Society