Scientists Showcase a New Eco-Friendly Coating That Could Make Polyurethane Foam, Etc., Flame Retardant

Scientists have now demonstrated a new coating designed to limit the flammability of wood used in construction, which could provide people with more time to escape a fire and also hinder its spread. This environmentally friendly flame retardant could also be applied to other flammable materials such as polyurethane foam, textiles and three-dimensional (3D) printed parts.

According to the National Fire Protection Association, home 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 approach is to make building materials less combustible. This is the goal of Dr Thomas Kolibaba, who is creating a new coating for these materials.

This treatment can be deposited by impregnation, spraying or pressure treatment and can make houses safer. This coating reduces the spread of flames and the production of smoke, which can limit damage and give people more time to evacuate.

Dr Thomas Kolibaba is a graduate student and postdoctoral researcher in the Grunlan lab at Texas A&M University.

Dr Jaime Grunlan, the project's principal investigator, observed that the composition of the new coating is environmentally friendly and potentially less expensive than most existing fire retardant treatments.

Kolibaba conducted the research as a graduate student and postdoctoral researcher in Grunlan's lab, building on the polyelectrolyte coating technology conceived by the team in 2009 and later improved by other scientists.

Many such coatings are achieved by immersing materials or other things in a solution consisting of a polymer with a large positive charge, then in another solution consisting of a polymer with a large negative charge, and then repeating these steps to achieve the preferred thickness.

The opposing charges attract the polyelectrolyte molecules in the alternating layers to form a complex on the surface of the article, creating a coating that can extinguish flames.

Thomas Kolibaba was keen to extend this treatment to wood, but the multi-step approach was not feasible for the manufacturer as the wood would take a long time to absorb the chemicals.

With additional research he adapted Grunlan's alternative method and was able to reduce the number of steps to two: one dip for applying the wood and a second dip in a different solution that treats the coating by switching the pH level.

However, the second solution always became viscous, so the reconstituted process was still not suitable for consumer or industrial applications.

In a recent change, Thomas Kolibaba has overcome this problem and says the process will be easily adopted by consumers or industry.

He immerses the plywood in an aqueous solution consisting of the monomer hydroxyethyl methacrylate phosphate (HMP), the positively charged polymer polyethyleneglycol (PEI) and a photoinitiator called TPO.

Instead of dipping the wood into the solution a second time to cure it, he exposed it to ultraviolet (UV) light for several minutes. This allows the TPO to turn the HMP into a negatively charged polymer, which then forms a polyelectrolyte complex with the PEI.

The resulting coating is transparent and only a few microns thick, so it does not change the appearance of the wood, but only slightly increases its weight.

In laboratory flame tests, the treated wood reduced the amount of heat emitted during combustion and quickly formed a surface charcoal layer that protected the underlying wood - properties that can contain the spread of fire and damage.

It also reduced smoke production by 56%, which is a very significant improvement.

Compared to the team's previous coating, which was held together by ionic bonds, this coating was covalently bonded. As a result, the Grunlan lab speculates that it is water resistant - and therefore durable - and perhaps also fungus and water resistant.

Industrial users could use this coating on building materials such as dowels and other framing, or oriented strand board (an engineered wood similar to particle board.) Thomas Kolibaba says homeowners could use backpack sprayers to protect current structures such as barns or fences, which have been shown to spread wildfires.

Other possible applications include polyurethane foams and textiles for household goods, clothing and in the aviation and automotive sectors, according to Grunlan Laboratories.

Kolibaba added that UV-cured polyelectrolytes could also be used as a resin to make 3D printed parts that are flammable when produced with conventional resins. This could be a major advantage in aerospace applications, such as the International Space Station, he observed.