Sprayable gel protects buildings from wildfire damage

Published on 21st August in Advanced Materials, the study reveals that this innovative gel offers longer-lasting and more effective protection than existing commercial solutions.

Eric Appel, associate professor of materials science and engineering at Stanford, and senior author of the study, explained the limitations of current gels: “Under typical wildfire conditions, current water-enhancing gels dry out in 45 minutes. We’ve developed a gel that would have a broader application window – you can spray it further in advance of the fire and still get the benefit of the protection – and it will work better when the fire comes.”

Long-lasting protection

Water-enhancing gels are typically made from super-absorbent polymers, similar to those found in disposable diapers. When mixed with water and sprayed onto buildings, these polymers swell into a gel-like substance that clings to the surface, creating a wet barrier. However, in wildfire conditions – where temperatures can reach 100°C, with high winds and zero humidity – these gels dry out quickly, losing their effectiveness.

The gel developed by Appel’s team takes this concept further by incorporating silica particles in addition to the cellulose-based polymer. When exposed to heat, the gel undergoes a transformation. As Appel explained: “When the water boils off and all of the cellulose burns away, we’re left with the silica particles assembled into a foam. That foam is highly insulative and scatters heat, completely protecting the material underneath.”

This process creates an aerogel, a porous and lightweight solid that is a highly effective insulator. Silica aerogels, known for their use in space applications, offer exceptional resistance to heat transfer, making them an ideal solution for wildfire protection.

Lead author of the study, Changxin ‘Lyla’ Dong, highlighted the significance of this breakthrough: “We have discovered a unique phenomenon where a soft, squishy hydrogel seamlessly transitions into a robust aerogel shield under heat, offering enhanced and long-lasting wildfire protection. This environmentally conscious breakthrough surpasses current commercial solutions, offering a superior and scalable defence against wildfires.”

Testing and effectiveness

To test their new gel, the researchers applied various formulations to plywood and exposed them to the direct flame of a gas hand-torch, which burns at temperatures higher than those of wildfires. Their most successful formulation withstood the flame for more than seven minutes before the plywood began to char. In contrast, commercially available gels lasted less than 90 seconds under the same conditions.

Appel emphasised the importance of the aerogel’s unique properties: “Traditional gels don’t work once they dry out. Our materials form this silica aerogel when exposed to fire, which continues to protect the treated substrates after all the water has evaporated. These materials can be easily washed away once the fire is gone.”

A serendipitous discovery

This breakthrough builds on Appel’s earlier work with wildfire prevention. In 2019, his team developed gels that could hold fire retardants on vegetation for extended periods, preventing ignition in wildfire-prone areas. However, the discovery of this new gel’s fire-resistant properties was unplanned.

Appel recounted: “We’ve been working with this platform for years now. This new development was somewhat serendipitous – we were wondering how these gels would behave on their own, so we just smushed some on a piece of wood and exposed it to flames from a torch we had lying around the lab. What we observed was this super cool outcome where the gels puffed up into an aerogel foam.”

Following this discovery, the team spent several years refining the gel’s formulation to ensure stability in storage, ease of application with standard equipment, and strong adhesion to various surfaces. The gel is composed of nontoxic materials that have been approved for use by the U.S. Forest Service, and tests have shown that it breaks down easily in the environment through microbial action.

Appel expressed hope for the future of the technology: “They’re safe for both people and the environment. There may need to be additional optimisation, but my hope is that we can do pilot-scale application and evaluation of these gels so we can use them to help protect critical infrastructure when a fire comes through.”