おがくずを防火材に変える(Turning sawdust into fire protection materials)

2026-03-19 スイス連邦材料試験研究所(EMPA)

The researchers’ new material exhibits excellent fire-retardant properties. Image: Maximilian Ritter / from R Kürsteiner et al. Chem Circularity 2026, CC BY 4.0

＜関連情報＞

• https://www.empa.ch/web/s604/schwer-entflammbare-holzwerkstoffe
• https://www.cell.com/chem-circularity/fulltext/S3051-2948(25)00004-0

酵素を介したリグノセルロース系材料の難燃性で完全リサイクル可能な鉱物バインダーによる固化 Enzyme-mediated consolidation of lignocellulosic materials with a flame-retardant and fully recyclable mineral binder

Ronny Kürsteiner ∙ Dan Vivas Glaser ∙ Maximilian Ritter ∙ … ∙ Federico Carosio ∙ Ingo Burgert ∙ Guido Panzarasa

Chem Circularity  Published:January 26, 2026

DOI:https://doi.org/10.1016/j.checir.2025.100004

Context & scale

Sawdust is a major lignocellulosic by-product of the wood-processing industry, and millions of tons of it get downcycled by incineration every year. This study investigates the upcycling of softwood sawdust by means of struvite, resulting in inorganically bound hybrid materials with functional properties. The use of ureolytic protein bodies extracted from watermelon seeds, an agricultural by-product, allows for control of struvite crystallization, forming large crystals. As a result, the sawdust is efficiently consolidated even at a low struvite-to-sawdust ratio of 0.65 by weight. The struvite crystals conform to the rough surface topography of the sawdust and grow into accessible lumina (pores in the wood structure), leading to strong mechanical interlocking. The resulting composites are mechanically robust with a compressive strength of ∼4.5 MPa at ∼780 kg m⁻³ independent of the sawdust particle size. Struvite is an active inorganic flame retardant, and its homogeneous distribution in the hybrid composite confers outstanding flame-retardant behavior to the material and a fire-shielding ability as a result of efficient char-layer formation. The material could find application in internal walls because of its excellent fire protection and, after use, could be re-used for soil remediation given that struvite acts as a slow-release fertilizer. Alternatively, the struvite binder can be fully recycled under mild aqueous conditions while retaining its mechanical performance, marking a significant step toward a circular materials economy. The recovered sawdust could then be burned for energy generation (as it was originally destined) or potentially used for the fabrication of new composites. The mild conditions required for the binder recovery make the recycling of spent composites feasible and facilitate the use of alternative struvite sources, such as precipitates from wastewater facilities, as precursor materials.

Highlights

• Recyclable mineral binder consolidates sawdust into robust hybrid composites
• Enzyme-mediated phase transformation allows controlled struvite crystallization
• Hybrid composites show excellent fire resistance at low binder content
• Binder recovery under mild aqueous conditions enables circular materials economy

Summary

The wood industry produces enormous quantities of lignocellulosic by-products, such as sawdust, and their incineration for energy recovery results in substantial carbon emissions and the loss of valuable raw materials. Here, we introduce struvite as a fully recyclable inorganic binder for the consolidation of sawdust into high-performance hybrid materials. The mineral binder is produced in situ by an enzymatically induced solution-mediated phase transformation driven by ureolytic protein bodies extracted from watermelon seeds. The resulting material exhibits excellent fire resistance with a long time to ignition (51 ± 1 s), low peak heat release (118 ± 2 kW m⁻²), and fast flame self-extinction due to efficient char-layer formation. Moreover, it displays high compressive strength (4.71 ± 0.37 MPa). Crucially for sustainability, the struvite binder can be recovered under mild aqueous conditions without loss of performance, offering a valid path toward a circular materials economy.