Making safer, easier-to-apply flame retardants

There’s a good chance that you spend at least part of your day sitting on polyurethane foam. The foam is ubiquitous in upholstery across the world—in cars, couches, bedding, and more. Unfortunately, it is also highly flammable. Halogenated flame retardants historically have been added to the foam to prevent fires, but they’ve also been shown to be harmful to human and environmental health, leaving a demand for safer options.

In a talk delivered Thursday at the American Chemical Society Fall 2024 meeting in the Division of Polymer Chemistry, a team from materials scientist Jaime Grunlan’s lab at Texas A&M University presented their latest flame retardant. They say the product—a boron-containing retardant that gives polyurethane foam self-extinguishing properties—is easier to apply than other alternatives and safer than halogenated retardants.

Scientists in Grunlan’s lab have also been working for over a decade to find better flame retardants for wood and cotton, as well as foam. While their earlier foam retardants protected against burning, they required several more steps to install. Scientists would need to dip the foam repeatedly in alternating positively and negatively charged polyelectrolyte solutions to slowly build multiple protective layers.

Their more recent work, by comparison, includes fewer steps. The researchers dunk the foam into a pot of a polyelectrolyte solution at room temperature just once to apply a protective coating.

“If you have a jar, you mix the coating, then you literally just dip the [foam] into the coating. Or you hook the solution up to a spraying device, and you spray it on,” Grunlan said. “It’s quite simple and straightforward, and all of that is done at room temperature with no special environment.”

The team experimented by adding different concentrations of ammonium pentaborate to the retardant. The additive contains boron and is believed to be less toxic than compounds in halogen-based retardants. They observed that when they lit the foam with a butane torch, samples coated with higher levels of ammonium pentaborate preserved more of the foam and gave the foam the ability to extinguish itself (ACS Appl. Polym. Mater. 2024, DOI: 10.1021/acsapm.4c00400).

“I think we have the most benign and easiest to apply and most effective system,” Grunlan said. “In terms of processing time and effort, it’s very convenient compared to the layer-by-layer technology.”

Grunlan said he is in talks with companies about scaling up the technology to apply it to commercial products. He added that the team can continue to tweak the retardant since the coating made the foam heavier than they would prefer.

Kelvin Shen, a chemist and fire-retardant expert who retired from U.S. Borax in 2006 and is now a consultant for the polymer industry, said the results were “very impressive.” He added that he’d be curious to see how well the technology would transition to commercial applications on larger foam products.