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Catastrophic residential fires and wildfires have a significant impact in terms of death and injury, as well as property loss.

Coated wood (left) can resist flames, limiting fire damage, unlike bare wood (right). Image credit: Ethan Iverson.

Currently, scientists are illustrating a new type of coating designed to limit the flammability of wood used in construction, possibly providing extra time for fires to escape and also preventing its spread. The environmentally friendly flame retardant could also be applied to other flammable materials, such as polyurethane foam, textiles and three-dimensional (3D) printed parts.

The scientists presented their results at the spring conference of the American chemical society (ACS). ACS Spring 2022 is a hybrid conference that will be held in person and virtually between March 20and and 24andwith on-demand access available between March 21st and April 8and. The meeting covers over 12,000 presentations on a wide range of scientific topics.

According to the National Fire Protection Association, residential fires account for the majority of fire deaths and cause billions of dollars in property damage each year. Installing smoke detectors and fire sprinklers can help, but another method is to make building materials less flammable. This is the goal of Thomas Kolibaba, Ph.D., who creates a new coating for these materials.

This type of treatment, which could be deposited by dipping, spraying or pressure treatment, could make homes much safer. The coating could reduce flame spread and smoke production, which could limit damage and give people more time to evacuate.

Thomas Kolibaba, Ph.D., Graduate Student and Postdoctoral Researcher, Grunlan’s Lab, Texas A&M University

Unlike the majority of existing flame retardant treatments, its components are environmentally friendly, and it could also be less expensive, observes Jaime Grunlan, Ph.D., the project’s principal investigator.

Kolibaba performed the research as a graduate student and postdoctoral researcher in Grunlan’s lab at Texas A&M University, developing the polyelectrolyte coating technology designed by the team in 2009 and later improved by other scientists.

Many of these coatings are created by dipping a material or other things into a solution that includes a polymer with lots of positive charges, which is then followed by soaking in another solution that includes a polymer with lots of negative charges, and then passing them over them. steps again and again to achieve the desired thickness.

The opposing charges draw the polyelectrolyte molecules in the alternating layers together in complexes on the surface of the article, developing a coating that can extinguish a flame.

Kolibaba wanted to extend this treatment to wood, but the multi-step method was not feasible for growers because the wood needs a long time to absorb these chemicals. With further research, he adapted another Grunlan method and was able to reduce the steps to two: one dip to coat the wood and the second dip in a diverse solution to treat the coating by changing the pH.

However, this second solution became a sticky mess, so the restructured process was still not suitable for consumer or industrial applications.

In the most recent modification, which will be demonstrated at ACS Spring 2022, Kolibaba has overcome this problem with a process that he believes would be easy for consumers or industry to adopt.

He soaked plywood in an aqueous solution comprising the monomer hydroxyethyl methacrylate (HMP) phosphate, the positively charged polymer polyethyleneimine (PEI), and a photoinitiator called TPO.

Rather than dipping the wood a second time in a solution to harden, he placed it under ultraviolet (UV) light for a few minutes. This caused the TPO to transform the HMP into a negatively charged polymer, which then developed a polyelectrolyte complex with the PEI. The subsequent coating was transparent and a few micrometers thick, so it did not alter the appearance of the wood and only added marginally to its weight.

Treated wood, in laboratory flame tests, decreased the amount of heat emitted during combustion and quickly developed a surface layer of char that protected the underlying wood – properties that could curb the spread of fire and damage.

It also reduced smoke production by 56%, an unusually high degree.

Thomas Kolibaba, Ph.D, Graduate Student and Postdoctoral Researcher, Grunlan’s Lab, Texas A&M University

Unlike the team’s previous coatings, which are bound together by ionic bonds, this coating is covalently bonded. Thus, Grunlan assumes that it is water-resistant – and therefore durable – and possibly also antifungal and water-repellent.

Industrial users could apply the coating to building materials, such as wooden studs and other structural work, or oriented strand board (a type of engineered wood similar to particle board). Homeowners could use a knapsack sprayer to protect current structures like barns or fences, which have been set up to spread wildfires, Kolibaba says.

Other possible applications include polyurethane foam and textiles for furniture, apparel, and the aviation and automotive sectors, says Grunlan.

UV-curable polyelectrolytes could also be used as a resin to create 3D-printed components, which are flammable when produced using traditional resins, adds Kolibaba. This could be mainly advantageous in the aerospace domain, for example, the International Space Station, he observes.

Scientists acknowledge funding and support from Texas A&M University.

New lightweight coating to reduce wood flammability

Video credit: ACS.