Few things are scarier than a blaze inside your house — and if your house is made of wood, that’s even worse. Untreated wood is particularly vulnerable, and even some coatings provide only limited protection. But a new chemical devised by researchers at Texas A&M University could change all that.
The new coating builds on technology developed in 2009 at the same university and later improved by other researchers. The main principle behind the coating is a “double dip” — first, a dip in a solution containing one polymer with a strong positive charge, followed by another dip in a solution containing a strong negative charge (the process can be repeated several times to get the desired thickness coating). The opposing charges in alternating layers form a coating that can extinguish a flame.
“We’ve been working on water-based, environmentally-benign flame retardant treatments in my lab for more than a decade,” says Jaime Grunlan, the project’s principal investigator, for ZME Science. “More recently, due to the many devastating fires we’ve seen in California, Washington, Australia, Paris, and London, we’ve turned some of our attention to building materials and the urban-wildlife interface.”
It doesn’t have to be strictly dipping, either.
“This type of treatment, which could be deposited via dipping, spraying or pressure treatment, could make homes much safer,” says Thomas Kolibaba, one of the study authors. “The coating could reduce flame spread and smoke production, which could limit damage and give people more time to evacuate.” Unlike most current fire retardant treatments, its ingredients are environmentally benign, and it might also cost less, notes Kolibaba.
Kolibaba has developed several successful flame retardant treatments for various wood substrates. This time, he was interested in extending the treatment to wood. The main problem was that the multiple dips takes a lot of time, which makes it impractical for the wood industry. Kolibaba managed to reduce the process to just two steps: an initial dip, after which the wood was treated with a specialized solution that cures the coating by changing its pH, making it more resilient. This way, multiple repeats of the process aren’t necessary.
However, the second solution kept turning into “a sticky mess”, so the process wasn’t efficient or convenient for commercial applications.
The new solution is much more versatile and resilient, which makes it easier for industries and consumers to adopt. Essentially, the wood was coated in an aqueous solution containing the positively charged polymer polyethylenimine (PEI), the monomer hydroxyethyl methacrylate phosphate (HMP), and a photoinitiator known as TPO. Then, instead of a second dip, the wood was simply exposed to ultraviolet (UV) light for a few minutes.
This UV exposure turns the HMP into a negatively charged polymer, producing a coating similar to the multi-layered positive-negative solutions in the first versions of the treatment. The resulting coating is transparent and only a few micrometers thick and doesn’t significantly change the wood’s appearance or weight.
“With this latest UV-curable treatment, our polyelectrolyte technology can be deposited in a single step, allowing for easy commercialization and possibly even personal use with a simple sprayer,” says Grunland. “The treatment densifies the wood a bit, which makes it appear to be a bit stronger and stiffer, but it is a surface treatment, so the greater the thickness of the wood piece, the less the impact on strength/stiffness.”
When the coating was put to the test, it formed a surface layer of char but protected the underlying wood.
“It also reduced smoke production by 56%, an unusually large degree,” Kolibaba says. Unlike the team’s prior coatings, which are held together by ionic bonds, this one is covalently bonded. So Grunlan expects it to be water-resistant — and therefore durable — and possibly also water-repellent and antifungal.
Wood is a major construction material, the researchers say, especially in the US. It’s used for house frames, fencing, telephone poles, so it is a good substrate to “focus our efforts on”.
The method could be used to protect structural beams, as well as fences or barns, which are prone to propagating fires. However, the approach isn’t necessarily restricted to wood — it could be deployed to textiles or the automotive and aviation industries, the researchers say. It could even be used to 3D print fire-resistant structures, the team says. The coating is also eco-friendly, and can be cost-efficient for a number of different products, the researchers conclude.
“I think the bigger point is that it does not negatively impact anything about the wood and uses relatively benign ingredients. This can absolutely be made in a cost-efficient manner and we envision it will be used for pressure treated wood used for buildings, plywood, oriented strand board (OSB), fencing, etc,” Grunlan added in an email.
The study has not yet been peer-reviewed and was presented at the spring meeting of the American Chemical Society. The study will be soon submitted to a peer-reviewed journal, the researchers note.