Flame-retardant coating stops even wood from catching fire

By Fábio De Castro  |  FAPESP Innovative R&D – Galembetech, a startup located in Campinas, São Paulo state (Brazil), has developed a novel flame-retarding material via an innovative strategy based on the use of cellulose fibers to reassemble graphite crystals. The nanotechnological product, developed with support from the FAPESP Innovative Research in Small Business Program (PIPE), is being used in the manufacturing of coatings that prevent fire from spreading on wood surfaces and buildings, among other applications.

According to Fernando Galembeck, founder of the firm and a retired professor at the University of Campinas (UNICAMP), the novel fire retardant is based on exfoliated and reassembled graphite (ERG), and is part of a cellulose and graphite product development platform.

“Basically, we use cellulose fibers to exfoliate or, as it were, to ‘dismantle’ graphite crystals. When the coating is applied and dries out, the crystals reassemble to form a laminated graphite layer with exceptional thermal and electrical conductivity and flame resistance,” Galembeck said.

Graphite is an ultralight mineral made up of stacked graphene sheets like a sheaf of writing paper or a pack of cards, he explained. The graphene sheets have outstanding mechanical, electrical and thermal properties but are extremely thin. One of the problems with graphene is that if several sheets are used to increase thickness, the material loses some of its special properties.

“Our exfoliation strategy enables us to obtain reassembled graphite film with much lower strength than graphene. As a result, we can produce thicker film that conducts electricity and heat very well,” he said.

Focus on wood products

When a wooden surface is exposed to flames, it heats up until it catches fire. This causes minor and major disasters, such as the fires that destroyed the National Museum in Rio de Janeiro and severely damaged Notre-Dame Cathedral in Paris. The conductivity of ERG, in contrast, lets heat spread over the entire surface, protecting the wood from the flames.

“A layer of ERG on wood conducts heat very efficiently away from the point of contact with the flames, and the material doesn’t get hot enough to catch fire,” Galembeck said. “In addition, the ERG layer insulates the wood by preventing oxygen in the air from interacting with it. There’s no fire without oxygen.”

Thanks to the properties of this material, the wood products industry is very interested in the product. In 2021, Brazilian exports of wood products except paper and pulp grew 27% year over year, reaching USD 381 million.

“We focus on manufacturers of industrial wood for doors, posts, joists, beams and so on. Right now, we’re presenting the product to the market, contacting prospective customers and discussing the details of possible applications and joint development agreements taking into account any necessary adaptations for each user,” he said.

Laboratory tests show that ERG-coated wood is flame retardant, but this performance is assured only by bench assays. The main attraction for the industry, according to Galembeck, is that in second-half 2020, the São Paulo State Technological Research Institute (IPT) certified that Galembetech’s product achieved the highest rating established by technical standards on flame retardants.

“The difference between this certification and the lab test results is that the former has legal value because it was issued by an accredited institution following strict guidelines. We can therefore say with a high level of confidence that our coating is a flame retardant,” Galembeck said.

Intellectual property rights to exfoliated graphite dispersion production and applications are protected by patents in Brazil and abroad, and by industrial secrecy covering the preparation and application of the company’s products, he explained. The material will be produced by both Galembetech and partner companies.

“We have offices and a lab for dry activities in Campinas. Production happens at our partner SP Tecnologia’s plant in Mogi Mirim [a city near Campinas], where we also produce coated materials. Our own production capacity is about 4 metric tons per month. When demand exceeds this capacity, we call on our partners, who have larger plants and can produce much larger batches,” Galembeck said.

Coating production

Support from FAPESP via PIPE, starting in 2018 and ending in second-half 2021, enabled the firm to set up a manufacturing facility in Mogi Mirim, where coatings will be developed and produced, and to purchase part of the equipment, according to Galembeck.

“When we realized we’d discovered a process to produce a highly effective electrically conductive coating, we submitted our first application for funding for product development and won the support of PIPE.”

The project turned out to involve far more than the fire retardant, Galembeck explained, as it also resulted in the creation of a development platform, given the several other applications of such coatings in different areas envisaged by the firm’s scientists.

“We work with a small number of raw materials in several projects with highly differentiated applications, including some in energy and environmental decontamination, but the fire-retardant project is at the most advanced stage of product development,” Galembeck said.

Graphite exfoliation

Galembetech opened for business at the start of 2016, and the research that was later to result in the ERG technological innovation began in the following year, with Leandra Pereira dos Santos and Elisa Silva Ferreira participating. Santos finished her doctorate in chemistry at UNICAMP in 2013, with Galembeck as her thesis advisor, and joined the firm while she was doing postdoctoral research. Ferreira earned a master’s degree at UNICAMP in 2016, also with Galembeck supervising.

“Elisa’s master’s dissertation provided the seed for this project, with the discovery that graphite can be exfoliated with cellulose to produce a film,” Galembeck said. “At the time, we had no idea how many applications would come out of it. Leandra was already with the firm then and conducted the first characterization of the material in terms of fire-retarding properties.”

Initially, the focus was on researching cellulose’s unique property of not dissolving in practically anything, he recalled. “Why that’s so was a scientific puzzle for many years. Finally, Swedish chemist Bjorn Lindman hypothesized in 2010 that cellulose dissolves in hardly anything because it’s amphiphilic – partly compatible with oils, preventing it from dissolving in water, and partly with water, so that it doesn’t dissolve in anything oily.”

Lindman’s theory was met with derision for a time, but is now accepted by most scientists and has been validated experimentally on several occasions. “First of all, in the lab, I proposed an entirely academic hypothesis, which was that if Lindman was right, cellulose should entwine with other molecules that also had this nanohydrophobic property. The most logical possibility to test this hypothesis was to use graphite,” he said.

Cellulose fiber is made up of long chains that are stacked on top of one another and bonded via hydrophobic faces, he explained, while graphite consists of many flat sheets, stacked like a pack of cards. Scientists have known for some time that a small amount of caustic soda dissolved in water separates cellulose chains. With these elements, he conducted a series of experiments.

“The cellulose chains separated the graphite sheets, bonding with and overlaying them as if they were shuffled or interleaved,” Galembeck said. “We found that when a solution of cellulose with a little caustic soda was mixed with the graphite, this interleaving occurred spontaneously. The cellulose chains literally inserted themselves in between the graphite sheets.”

This tendency for two materials to mix spontaneously, he added, results in a straightforward fabrication process that does not require the use of ultrasound, common in such operations, or high temperatures, for example.

“The process is surprisingly simple, in fact, but the success of the result is evident. We can produce sheets of the material up to 5 meters in length for application to wood, paper, fabric and cement,” he said. “We simply prepare the cellulose solution and add graphite while stirring. The conditions need to be controlled to prevent lumping, but this is normal for the paints and coatings industry.”

The cellulose fibers break down the graphite crystals and form layers of cellulose interleaved with graphite. Because cellulose is water compatible, these smaller graphite crystals are suspended in the liquid coating, which forms a film when dry.

“When the product is applied to a surface, the graphite crystals that were in the liquid medium dry out, and a very important process occurs. The caustic soda kept the cellulose dissolved so that the graphite remained dispersed. When the coating dries, the caustic soda comes into contact with carbon gas in the air and is converted into sodium bicarbonate, an inoffensive substance, eliminating the hazardousness of caustic soda,” Galembeck explained.

Once the coating is applied, the caustic soda disappears and the cellulose becomes insoluble. Instead of being a graphite dispersant, it therefore becomes graphite glue. “From here on, we can put the graphite in the water and it will no longer disperse,” he said.

Prizes

With this project, Galembetech won a prize awarded in December 2020 by the Brazilian Paints and Coatings Industry Association (ABRAFATI).

Also in 2020, Galembetech was awarded the Kurt Politzer Innovation Prize for Startups by the Brazilian Chemical Industry Association (ABIQUIM), for the establishment of a platform for developing nanomaterials from renewables.

Professor Galembeck was awarded a prize by Companhia Brasileira de Metalurgia e Mineração (CBMM) for outstanding technological development.