A 30-nm-thick polymer coating can prevent the spread of flames on foam used in home furnishings (ACS Macro Lett., DOI: 10.1021/mz400105e). The coating, which consists of a sulfur-based polymer and a carbohydrate polymer found in crustacean shells, could be an environmentally friendly alternative to the flame retardants used today in furniture foam, its developers say.
Furniture cushions are typically made of highly flammable polyurethane foam. To meet fire safety guidelines, manufacturers treat the foam with flame-retardant chemicals. Toxicologists and environmental scientists worry about these brominated chemicals because studies have shown that some can act as endocrine disrupters or lead to neurological problems. The European Union has banned several of the compounds, and regulatory agencies in the U.S. and Canada have started to scrutinize the chemicals’ use.
Jaime C. Grunlan, a mechanical engineer at Texas A&M University, wanted to find flame-retardant formulations that do not affect the foam’s stiffness and are less toxic than current compounds. The coating he and his team developed consists of polyvinylsulfonic acid (PVS) and chitosan, a long carbohydrate molecule derived from the shells of shrimp and other crustaceans.
To produce the coating, the researchers dip foam in water solutions of the two polymers. Chitosan is positively charged in water, whereas PVS is negatively charged. The oppositely charged polymers attract each other and become entangled, creating the coating. The 30-nm-thick film increases the weight of the foam by just 5.5% and doesn’t alter the foam’s stiffness.
The researchers tested the coating by exposing treated foam to a flame from a butane torch for 10 seconds. Whereas uncoated foam burned up completely, the fire on the coated foam went out once the researchers turned off the torch. It would take more than three times as much conventional flame-retardant material by weight to achieve the same effect, Grunlan says.
He explains that when PVS burns it gives off vapors of sulfur oxides, which are nonflammable. “This creates a gas blanket on the foam surface, cutting off oxygen and starving the fire,” he says.
Fireproof nanocoatings are cutting-edge technologies in the field, says Rick D. Davis, who works on clay-based nanocoatings in the flammability reduction group at the National Institute of Standards & Technology.
Grunlan’s nanocoating is novel because it’s the first to use sulfur-based gas to extinguish fire, Davis says. Both the clay-based and polymer nanocoatings, he says, are more effective and could be less toxic than commercially available flame retardants.