Sawdust to Fireproof Material: New Recyclable Building Composite Developed

Every year, millions of tons of sawdust—a byproduct of sawing timber—are generated globally. Traditionally, much of this material is burned for energy, releasing stored carbon dioxide into the atmosphere. Now, researchers at ETH Zurich and Empa have developed a process to transform this waste product into a robust, fire-retardant, and recyclable material, offering a potential step forward for both construction and environmental sustainability.

The innovation centers around combining sawdust with struvite, a crystalline mineral composed of ammonium magnesium phosphate. Struvite is already known for its fire-resistant properties, but previously, effectively binding it with sawdust proved challenging due to the mineral’s crystallization process. The team overcame this hurdle by utilizing an enzyme extracted from watermelon seeds to control how the struvite crystals form. This allows for the creation of larger crystals that fill the spaces between sawdust particles, creating a strong composite material.

A Novel Binding Agent: Struvite and Watermelon Seed Enzymes

The process involves pressing the sawdust and struvite mixture for two days, followed by room-temperature drying. According to Ronny Kürsteiner, who led the development as part of his doctoral thesis, the resulting material demonstrates compressive strength exceeding that of the original spruce timber when measured perpendicular to the grain. This makes it particularly well-suited for interior fittings where fire resistance is crucial. The research, published in Chem Circularity, details the method and its potential applications.

Struvite’s fire-retardant qualities aren’t simply about preventing ignition. When exposed to heat, the mineral decomposes, releasing water vapor and ammonia. This process actively cools the surrounding environment and creates non-combustible gases that displace oxygen, hindering fire spread and promoting char formation. Testing using a cone calorimeter—a standardized fire exposure test—showed the struvite-sawdust composite took over three times longer to ignite than untreated spruce. As reported by Phys.org, this self-protective quality is a significant advantage.

Beyond Fire Resistance: Circularity and Environmental Benefits

The environmental advantages extend beyond reducing carbon emissions from burning sawdust. Conventional flame-retardant materials, like cement-bonded particleboards, often have a substantial carbon footprint due to the energy-intensive cement production process and their heavy weight. These boards typically contain 60 to 70% cement. The new struvite-sawdust composite, in contrast, requires only 40% binder, resulting in a significantly lighter material.

Perhaps most importantly, the material is designed for recyclability. Unlike cement-bonded particleboards, which often end up as waste, the struvite sawdust board can be broken down and its components reclaimed. Mechanical grinding combined with gentle heating (above 100°C/212°F) releases ammonia and allows for the separation of sawdust. The reclaimed materials can then be used to create new struvite composites, closing the loop and contributing to a circular economy. The released ammonia can even be repurposed as a natural fertilizer, providing a slow-release source of phosphorus for plant growth.

Scaling Up Production and Addressing Cost Considerations

While the initial results are promising, scaling up production presents challenges. The primary hurdle is the cost of struvite compared to more common binders like polymers or cement. However, the researchers are exploring a potential solution: utilizing struvite recovered from sewage treatment plants, where it accumulates and causes blockages. As Futurity reports, tapping into this existing waste stream could significantly reduce the cost of the binder, making the material more competitive.

Further testing is too needed to confirm the material’s fire protection class and ensure it meets industry standards. Larger-scale flame retardancy tests are planned to validate the initial findings. The team is also focused on optimizing the production process to improve efficiency and reduce costs.

Implications for the Construction Industry and Beyond

The development of this sawdust-based fireproof material represents a significant step towards more sustainable building practices. By transforming a waste product into a valuable resource, it addresses both environmental concerns and the need for safer construction materials. The potential to utilize recovered struvite from wastewater treatment plants further enhances its sustainability profile.

The researchers at ETH Zurich and Empa are continuing to refine the process and explore potential applications beyond interior fittings. The material’s unique properties and environmental benefits suggest it could play a growing role in the future of construction and materials science.

Looking Ahead: Material Cost and Wastewater Integration

The long-term viability of this innovation hinges on reducing the cost of struvite. Successfully integrating wastewater treatment plant byproducts into the production process could be a game-changer, transforming a waste disposal problem into a valuable resource stream. Further research will focus on optimizing this integration and ensuring the quality and consistency of the recovered struvite.