Author: Lena Barner-Rasmussen
Making materials flame retardant is not a straight-forward affair. Sustainability, circularity and health issues need to be factored in along with the main task: making sure the material is as safe as possible should a fire occur. Professor Carl-Eric Wilén gives a glimpse in to the latest in the research on sustainable flame-retardant materials.
Every now and then we are reminded in the most gruesome way why the use of flame-retardant materials is of utmost importance.
The horrible 2017 Grenfell Tower accident in the UK was a stark reminder that the choice of materials used in buildings make a huge difference when it comes to fire safety. This horrible accident represented a paradigm shift: it made lawmakers truly wake up to the fact that legislation and safety standards are indeed needed.
The European Chemical Agency has a list with chemicals of high concern. A lot of flame-retardant substances are on that list, or risk being added in the near future. This has propelled research to find alternative substances for efficient flame-retardance.
At the Åbo Akademi University in Finland, Carl-Eric Wilén, Professor of Polymer Technology at the Centre of Excellence for Functional Materials (FUNMAT), and his colleagues are working with industry players, such as Walki, to develop a new generation of flame retardants that are not only efficient, but also minimise both environmental and health implications. The transition towards a circular economy also poses some additional challenges.
“If you want to recycle construction materials or cars for instance, you need to make sure that the process does not release hazardous chemicals”, explains Wilén.
Most materials can be made non-combustible with flame retardants, which is a substance that is added to a combustible material to prevent a fire from starting, slow its spread, extinguish it altogether or ideally hinder the fire from happening at all. A variety of different chemicals can act as flame retardants, and are often combined for effectiveness. While some flame-retardant substances suppress the chemical reactions in the flame by disrupting the production of free radicals and shutting down the combustion process, others release water molecules that cool the polymer and dilute the combustion process. A third type of flame retardant forms a protective barrier – or char – on the material to hinder the release of additional gases to fuel combustion.
“The problem is that a lot of flame-retardant substances are based on halogen, for instance bromine, phosphorus or boric acid”, explains Wilen.
As of 2021, the EU will require plastics containing flame retardants that are used in electronics to be marked with an abbreviation for the polymer they contain plus the letters “FR” and a code number for the flame retardant. Consumer and health advocates have welcomed this move as a way to limit the potential adverse effects that halogenated flame retardants have on human health and the environment.
Another challenge is that a big dose of these flame-retardant substances needs to be used to achieve the desired effect. That is why the current research around flame-retardant solutions also circles around efficiency.
“We want to use as little of the flame-retardant substance as possible”, explains Wilén. For that to occur, you need to come up with a completely new range of flame-retardant substances that are efficient in very small quantities.
“Some of the substances used right now require up to 60% of the substance. What we are aiming for lies somewhere between 1-5%.”
Professor Wilén is currently focusing on halogen-free novel sulfenamide, a substance that is less dangerous to both the environment and humans.
“These so-called radical generators are halogen free and efficient in small amounts.”
Although the building industry accounts for around 30% of flame-retardance substances used, there are many other applications where flame-retardant materials are important. With the rise of electric vehicles, the automotive industry needs to take a particular interest in flame-retardants as the battery can overheat, increasing the risk of a fire. So the materials in the car, from upholstery to underbody shields, need to be flame-retardant. Electrical appliances, cables and the different textiles also need to be made flame-retardant.
Walki is focusing on flame-retardance both for the construction and automotive industry, such as the Walki®Wall Tight FR G A2, a flame-retardant membrane based on lacquered aluminium layers laminated with strong glass fabric attached with a flame-retardant glue. For the automotive industry, Walki is offering next generation skins, i.e. coating materials. Extrusion coating allows several layers of substrates and polymers to be combined, enabling a wide set of applications.
For its Print Media XXL range, flame-retardant options for indoors and outdoors advertising displays are currently also under development.
When it comes to flame-retardance, there really is no one-solution-fits-all. In addition to sustainability, health, recycling and efficiency, the FR materials need to be suitable for the extrusion coating technology Walki uses.
Professor Wilén appreciates the collaboration with business life.
“It gives us a possibility to empirically test how our flame-retardants work on production lines where you use very high temperatures. Walki has been in the forefront when it comes to sustainable flame-retardants and the circular economy, and is eager to test new solutions.”
Taking the long view, what kind of flame-retardant solutions will we have in 25 years?
“The research will increasingly focus on coming up with materials that are inherently non-flammable. There are polymers that do not burn easily, and may even self-extinguish. But they are currently very expensive and difficult to process. So for now, we are focusing on sustainable, halogen-free flame-retardants that are efficient in small quantities, do not compromise the material’s qualities and are easily recycled.”