ETH Zurich and Empa Develop Recyclable Fire Retardant Building Material from Sawdust Using Innovative Mineral Binding Process

The researchers are using an enzyme extracted from watermelon seeds to control the crystallization of struvite in an aqueous suspension with sawdust. Image: Ronny Kürsteiner / from R Kürsteiner et al. Chem Circularity 2026, CC BY 4.0

(IN BRIEF) Researchers from ETH Zurich and Empa have developed a new fire-retardant and recyclable building material made from sawdust and the mineral struvite, using an enzyme derived from watermelon seeds to control the binding process. The innovation offers a sustainable alternative to traditional materials by reducing waste, extending the lifecycle of wood byproducts, and lowering environmental impact. The composite demonstrates strong mechanical properties and significantly improved fire resistance, delaying ignition and forming protective layers when exposed to heat. It also supports circular economy principles, as it can be broken down and reused or repurposed as fertiliser. While further development and cost optimisation are needed, the material has strong potential for future applications in the construction industry.

(PRESS RELEASE) DÜBENDORF, 20-Mar-2026 — /EuropaWire/ — Researchers from ETH Zurich and Empa have developed an innovative method to transform sawdust, a widely underutilised byproduct of timber processing, into a recyclable and fire-retardant building material, offering a new approach to sustainable construction and material reuse.

Sawdust is generated in vast quantities globally and is often disposed of through incineration, releasing stored carbon dioxide back into the atmosphere. The newly developed process instead converts this material into a durable composite by combining it with the mineral struvite, helping to extend its lifecycle and reduce environmental impact.

Struvite, a crystalline ammonium magnesium phosphate, has long been recognised for its fire-resistant properties. However, integrating it effectively with sawdust has historically been challenging due to its crystallisation behaviour. The research team addressed this issue by introducing an enzyme derived from watermelon seeds, which allows precise control over the crystallisation process in a water-based mixture. This results in large mineral crystals forming between sawdust particles, binding them together into a solid structure. After pressing the material for two days, it is removed from moulds and dried at room temperature.

The resulting composite demonstrates strong mechanical performance, including improved resistance to pressure compared to natural spruce timber. Its fire-retardant capabilities are particularly notable, making it suitable for applications such as interior partitioning. When exposed to heat, the struvite component breaks down and releases water vapour and ammonia, which absorb heat and create a cooling effect. These gases also help to displace oxygen, slowing the spread of flames while encouraging the formation of a protective char layer that shields the material from further damage.

Testing conducted in collaboration with the Polytechnic University of Turin showed that the composite significantly delays ignition compared to untreated wood, withstanding exposure to heat for more than three times longer before igniting. Once combustion begins, the formation of an inorganic protective layer further enhances its resistance to fire.

Preliminary assessments indicate that the material could achieve similar fire protection classifications to cement-bonded particle boards, which are commonly used in construction. However, the new composite offers notable advantages, including reduced weight and a lower environmental footprint, as it requires a smaller proportion of binder and avoids the energy-intensive processes associated with cement production.

The material also introduces a strong circular economy potential. Unlike traditional composite boards that often end up in landfill, this new composite can be broken down after use. By mechanically processing and heating the material to slightly above 100 degrees Celsius, ammonia is released, allowing the separation of sawdust from the mineral components. The mineral can then be reprocessed and reused to create new composites, while also offering potential applications as a fertiliser due to its phosphorus content.

Looking ahead, the research team is focusing on refining and scaling up the production process. One of the key factors influencing commercial adoption will be the cost of struvite, which is currently higher than conventional binders. However, the researchers are exploring opportunities to source the mineral from wastewater treatment facilities, where it naturally accumulates and causes operational challenges, potentially creating a cost-effective and sustainable supply chain.

Media Contacts:

Prof. Dr. Ingo Burgert
Cellulose & Wood Materials
Phone +41 58 765 4434
ingo.burgert@empa.ch

Manuel Martin
Communications
Phone +41 58 765 4454
redaktion@empa.ch

SOURCE: EMPA