Executive Summary

Researchers at ETH Zurich and Empa have developed an innovative process that transforms sawdust into fire-resistant building materials using a mineral and a melon enzyme. The new composite offers superior fire protection, is significantly lighter than cement-bound alternatives, and is completely recyclable. The material could redirect millions of tons of sawdust waste generated annually back into the material cycle, combining climate protection with circular economy principles.

People

Topics

  • Fire protection & building materials
  • Circular economy & waste recovery
  • Wood composites & materials science
  • Enzymatic crystallization
  • Sustainable building material production

Clarus Lead

Researchers at ETH Zurich and Empa have developed a process that converts sawdust with the mineral struvite into fire-resistant composites. An enzyme derived from watermelon seeds controls crystallization and permanently bonds the sawdust particles. The material ignites only after more than 45 seconds, whereas untreated wood ignites after just 15 seconds – and can be completely recycled at the end of its life cycle.

Detailed Summary

Millions of tons of sawdust are generated worldwide each year, most of which is burned, releasing stored carbon dioxide. The new struvite-sawdust composite keeps this raw material in the material cycle longer. The central innovation lies in the use of an enzyme from melon seeds that controls the crystallization of the mineral struvite (ammonium magnesium phosphate) and creates large crystals that fill the voids between sawdust particles and bond them firmly together.

The material is pressed for two days, then dried at room temperature. It is more pressure-stable than untreated spruce wood and is particularly suitable for interior construction. Under heat, struvite decomposes and releases water vapor and ammonia – an endothermic process that absorbs heat and has a cooling effect. The released non-combustible gases displace air and prevent fire spread. In the standardized cone calorimeter test, the composite ignited only after more than 45 seconds, after which a protective layer of inorganic material and carbon quickly formed.

The struvite panels consist of only 40 percent binder and are thus significantly lighter than cement-bound particle boards (60–70% cement). Initial estimates suggest that the material achieves the same fire protection class as conventional cement particle boards – however, this must still be confirmed through larger flame protection experiments.

A decisive advantage: the material is completely recyclable. Through mechanical breakdown, heating to above 100°C, and sieving, sawdust and mineral components can be recovered. The mineral newberyite (starting material for struvite) is precipitated again and can be processed with new sawdust into composites. Additionally, the material acts as a natural long-term fertilizer in agriculture.

Key Findings

  • Enzymatic Control: A melon seed enzyme enables stable bonding of sawdust with struvite for the first time through controlled crystallization.

  • Superior Fire Protection: The composite ignites three times later than untreated wood and forms self-protective charring through endothermic mineral decomposition.

  • Lighter Alternative: With only 40% binder, the material is significantly lighter and more climate-friendly than cement-bound particle boards (60–70% cement).

  • Complete Circularity: Material can be mechanically and thermally broken down into raw materials and recycled indefinitely – in contrast to cement particle boards destined for hazardous waste landfills.

  • Dual Resource Use: Sawdust remains in the cycle longer; struvite from wastewater treatment plants could be developed as an additional raw material source.

Critical Questions

  1. Evidence/Data Quality: The fire protection class is based on "initial estimates" – when will the announced larger flame protection experiments be conducted and published to confirm equivalence with cement-bound particle boards?

  2. Scalability & Cost Factor: The text describes struvite as "relatively expensive" compared to polymer binders and cement – what concrete cost scenarios exist, and at what production volume does the material become economically competitive?

  3. Enzyme Availability: What is the globally available quantity of melon seed enzymes, and could scaling to industrial quantities lead to bottlenecks or new dependencies?

  4. Recycling Efficiency in Practice: The described recycling process occurs under controlled laboratory conditions – what is the practical recovery rate with mixed construction waste, and what contaminants could impair the process?

  5. Conflicts of Interest & Market Positioning: What patents do ETH Zurich and Empa hold, and are there already licensing agreements with building material manufacturers who produce cement particle boards and thus have competing interests?

  6. Long-Term Behavior & Moisture Resistance: How does the material behave with respect to moisture absorption and swelling deformation over several years, particularly in humid indoor spaces?

  7. Ammonia Release & Indoor Air Quality: What ammonia concentrations arise in case of fire or damage, and do these comply with indoor air quality limits?

  8. Alternative Binders: Were other mineral binders (e.g., magnesium oxides, geopolymers) tested with similar enzymes, and why is struvite the optimal solution?

Bibliography

Primary Source: Fire-resistant wood composites thanks to melon enzymes – Press Release ETH Zurich/Empa – https://www.news.admin.ch/de/newnsb/OQrHm2uHX9j_TpbynLKoy (March 19, 2026)

Verification Status: ✓ March 19, 2026

This text was created with the support of an AI model. Editorial responsibility: clarus.news | Fact-checking: March 19, 2026