April 4th, 2022
A new type of coating that could limit the flammability of wood used in construction has been introduced at the March meeting of the American Chemical Society. The team that developed this environmentally friendly flame retardant envisions that the coating could also be utilized for other flammable materials, such as textiles, polyurethane foam and 3D-printed parts.
In February 2019, researchers out of Texas A&M University were reportedly developing a new flame-retardant coating using renewable, nontoxic materials readily found in nature. Department of mechanical engineering professor Jaime Grunlan led the research (partnered with researchers at KTH Royal Institute of Technology in Stockholm, Sweden, led by Lars Wagberg, and including Thomas Kolibaba), which was published in Advanced Materials Interfaces, and said that successful development and implementation of the coating could provide better fire protection to different kinds of materials.
“These coatings offer the opportunity to reduce the flammability of the polyurethane foam used in a variety of furniture throughout most people’s homes,” Grunlan said in 2019. “The uniqueness in this current study lies in the use of two naturally occurring nanomaterials, clay nanoplatelets and cellulose nanofibrils. To the best of our knowledge, these ingredients have never been used to make a heat shielding or flame-retardant coating as a multilayer thin film deposited from water.”
Grunlan said that benefits from using this method include the coating's ability to create an oxygen barrier to plastic films and better fire protection at a lower cost than other, more toxic ingredients that are traditionally used.
To test the coating, researchers applied it to a flexible polyurethane foam, exposing it to fire using a butane torch to determine the level of protection the compounds provided.
“The nanobrick wall structure of the coating reduces the temperature experienced by the underlying foam, which delays combustion,” Grunlan said. “This coating also serves to promote insulating char formation and reduces the release of fumes that feed a fire.”
The next step was to transition the method into the industry for further development.
Just as in the early stages of the coating’s development, Grunlan notes that the ingredients of the fire retardant have remained environmentally benign, adding that now, they might also cost less.
Kolibaba carried out the research as a graduate student and postdoc in Grunlan’s lab at Texas A&M University, building on polyelectrolyte coating technology invented by the group in 2009 and later extended by other researchers. Typically, these types of flame retardant coatings are created by dipping the desired material in a solution containing one polymer with positive charges on it, followed by a dip in another solution containing a polymer with negative charges. The steps are then repeated until a desired film thickness is achieved.
Through this method, opposing charges draw the polyelectrolyte molecules in the alternating layers together into complexes on the item’s surface, forming a coating that can extinguish a flame. However, a problem that Kolibaba found with this method was that it wasn’t feasible for wood materials because it takes too long to soak up the chemicals.
In continuing his research, Kolibaba adapted a preexisting Grunlan technique, which cut the number of steps down to two: one dip to coat the wood, followed by a dip in a different solution to cure the coating by changing the pH. However, that option still proved problematic in that the resulting material was sticky and remained inconvenient for industrial or consumer applications.
After additional modifications, Kolibaba developed a new method that the team intends to present at ACS Spring 2022.
“This type of treatment, which could be deposited via dipping, spraying or pressure treatment, could make homes much safer,” said Kolibaba. “The coating could reduce flame spread and smoke production, which could limit damage and give people more time to evacuate. It also reduced smoke production by 56 percent, an unusually large degree.” Thanks to this attribute, Grunlan expects that the coating will also be water-resistant, meaning that in addition to limiting fire damage and spread, it could also serve as a water-repellent and antifungal coating.
