Fire retardant biocomposites: combining lightness and fire resistance

To slow the spread of fire, compounds called flame retardants are often used to treat materials to give them fire resistant properties. The problem is that some of these additives can be harmful for humans and polluting for the environment. To solve this problem, research focuses on the production of biobased materials designed to meet the dual criteria of effectiveness and environmental safety.

Flame retardants are widely used chemical compounds that reduce the flammability of furniture or electronic equipment. However, the use of some of these products has been criticized because they may pose risks to public health (neurotoxic, endocrine disruptor, carcinogenic, etc.) and the environment (bioaccumulation). In addition, some of these additives are derived from petroleum processing, a source of carbon emissions. The work by Laurent Ferry, a researcher in fire resistance for materials at IMT Mines Alès, aims to design non-toxic flame retardants using biocomposite materials and production methods that have less impact on the environment. “In particular, we are working on the use of plant by-products with minimal processing,” explains the researcher. Indeed, the simpler the extraction processes, the less energy they require and the lower the environmental impact.

Lignin, a molecule that gives plants their rigidity, and tannins, molecules involved in plant defense mechanisms against parasites, are two compounds that can be used to produce biobased flame retardants. To limit the number of processing stages, the molecules of interest are not completely isolated from certain plant compounds. This may reduce the effectiveness of the flame retardant but, as Laurent Ferry explains, “it is a compromise between effectiveness and the cost required to isolate the molecules of interest.”

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Chestnut tannins, an effective solution for delaying the spread of fire

One of the plant-based compounds that Laurent Ferry and Anne Bergeret, a researcher in Polymeric Materials, are interested in is chestnut tannins. Tannins are polyphenolic molecules. “When they burn, the polyphenolic compounds form a charred layer that limits the material’s contact with the air,” explains Anne Bergeret This means that there is less oxygen available to fuel combustion, which is thus inhibited.

Plant fibers with fire-retardant properties can be used to make biocomposites, which are lightweight materials combining resin and plant fibers. Firstly, “tannin is applied to plant fibers to improve their fire resistance,” says Anne Bergeret. These fibers are then added to a resin which serves as a binder to produce a lightweight, fire resistant biocomposite.

The effectiveness of flame retardants is defined at the nanoscopic level. To improve their performance, very small mineral particles can be incorporated into the resin. “The more we reduce the size of the incorporated mineral particles, the more we will slow the spread of the fire,” explains the researcher.

A multitude of application sectors

The developed materials can be used for manufacturing furniture, electronic devices or firefighters’ clothing. The public transport sector may also offer interesting avenues for development. “Composite materials are increasingly used in transport due to their lightness,” says Laurent Ferry. Biobased materials also make it possible to reduce environmental impact from the design stage, meaning that they offer the dual advantage of being both light and less damaging to the environment.

Fire retardant biocomposites could also be used to protect wood destined for the construction industry. However, the fire-retardant efficiency of the biocomposite materials developed at IMT Mines Alès is still only in the test phase. Once their effectiveness has been confirmed, studies will be carried out to “make sure that these products do not lead to health issues,” says Laurent Ferry. One possibility is the production of less toxic flame retardants than the ones currently on the market.

Many flame retardants used today contain halogenated compounds, some of which can be harmful to the health of people who are frequently in contact with them. “Flame retardants often contain bromine- or chlorine-based compounds. Some of these are endocrine disruptors and/or neurotoxic substances” explains Laurent Ferry. However, concerning his research on biobased flame retardants, “we must first prove their effectiveness at a larger scale than that of the laboratory before launching this type of study,” he says. 

Rémy Fauvel