Devastating forest fires are increasingly reducing residential areas to rubble and ashes. In order to make civilian structures immune to flames, researchers have now developed a special fire protection hydrogel that could be sprayed onto buildings at risk. The material, which initially contains water, turns into an aerogel when exposed to heat or when it dries out, and its silicon structures can effectively protect the substance underneath from igniting. The harmless protective material can then be easily washed off, say the developers.
The inferno continues to spread and eventually reaches human settlements: In the news, we are repeatedly confronted with the devastating consequences of forest fires. Studies show that the situation is becoming increasingly critical: Due to changes in natural forest ecosystems and the more frequent droughts as a result of climate change, the risk of forest fires is increasing significantly in some parts of the world. In addition to nature, people are also affected: in recent years, forest fires have caused enormous damage to houses and infrastructure. Therefore, some research teams are currently devoting themselves to developing new strategies to counter the threat potential of forest fires. This topic was also the focus of the August issue of bild der wissenschaft.
Fire protection effect despite drying out
The focus of the researchers led by Changxin Dong from Stanford University was now on the development of methods to protect buildings and infrastructure from approaching forest fires. The aim is to protect houses and other buildings from catching fire or heat damage by treating them with special substances. Water-based gel substances that can be sprayed onto surfaces are already in use for this purpose. These so-called hydrogels are made from superabsorbent polymers. Mixed with water and sprayed onto a building, they swell into a gelatinous substance that adheres to the surfaces and forms a moist protective layer. But the concept has so far had a significant disadvantage: hydrogels dry out quickly in the heat and the often strong air flow during fires and lose their effectiveness. “Under the typical conditions of a forest fire, the current hydrogels dry out within 45 minutes,” says senior author Eric Appel from Stanford University.
The researchers have therefore now transformed the concept into a version with sustainable effectiveness. Their idea was that when the hydrogel dries out, it should turn into a so-called aerogel, which can have a stable fire protection effect. In the development, they again used a water-containing polymer-based hydrogel as the starting material. However, they then added a crucial component to the mixture: particles made of silicon. The gelatinous mixture can then be sprayed onto surfaces as in previous versions and settle. The water contained can then perform its protective function against fire as before. But after it has evaporated, the system does not become ineffective: the silicon particles it contains form an aerogel as it dries out. “This material has a highly insulating effect and scatters heat, so that the substrate underneath is protected,” explains Appel. “We have therefore developed a gel that has a wider application window than before – you can spray it earlier in the event of a fire and still get protection,” says the researcher.
Efficient heat protection
The researchers documented how well the new material can protect against fire and heat stress through experiments in which they applied the gel to wood and exposed it to the particularly hot flame of a hand-held gas burner. The most effective formulation was able to protect the underlying wood from charring for more than seven minutes. A conventional hydrogel, on the other hand, only lasted for 90 seconds. “When exposed to heat, the new hydrogel transforms into a robust aerogel shield that can provide improved and long-lasting protection against fires. This breakthrough surpasses current concepts and could provide superior and scalable protection against forest fires,” Dong summarizes.
The researchers have also already succeeded in optimizing the formulation of the substance for use in fire protection by adding additional components: it can now be stored, is easy to spray with standard equipment and adheres well to all types of surfaces. Disposing of the protective layer after the fire has passed is also unproblematic, say the developers: the aerogel layers can be easily washed off and all the components they contain are harmless. “They are safe for both people and the environment,” emphasizes Appel. “Further optimization may still be necessary, but I hope that we will soon be able to use and evaluate these gels on a pilot scale so that we can use them to protect critical infrastructure in the event of fires,” says the scientist.
Source: Stanford University – School of Engineering, technical article: Advanced Materials, doi: 10.1002/adma.202407375