A team at the Chair of Wood Materials Science at ETH Zurich, together with Empa, developed a process to make a recyclable composite from sawdust and the mineral struvite. They use an enzyme extracted from watermelon seeds to control crystallization of struvite from a suspension of the precursor newberyite. The enzyme helps form large crystals that fill cavities between wood particles; the mixture is pressed and then dried at room temperature.
The material is stronger under compression perpendicular to the grain than original spruce timber, according to Ronny Kürsteiner, who developed the process for his doctoral thesis. Tests in a cone calorimeter at the Polytechnic University of Turin showed untreated spruce ignites after about 15 seconds, while the struvite sawdust composite takes more than three times as long to ignite. Once it burns, a protective layer of inorganic material and carbon forms quickly.
Initial estimates suggest the composite could reach the same fire protection class as cement‑bonded particleboards, but larger scale tests are required. The composite is lighter and easier to recycle, and struvite can also be used as a slow‑release fertilizer. Next steps include optimizing and scaling up production; cost of the binder will affect wider use.
Difficult words
- composite — Material made from two or more substances.
- crystallization — Process where solid crystals form from a liquid.
- enzyme — Protein that speeds up chemical reactions.
- precursor — Substance that comes before another substance.
- ignite — To begin burning or start a fire.ignites
- struvite — A mineral often rich in phosphorus and nitrogen.
- cone calorimeter — Device that measures how materials burn.
- binder — Substance that holds particles together in materials.
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Discussion questions
- Do you think a lighter, recyclable wood composite could replace some cement‑bonded boards? Why or why not?
- How important is slower ignition time for building materials in your opinion? Give one or two reasons.
- The enzyme in this project comes from watermelon seeds. Would the source of an ingredient affect your acceptance of a new material? Explain briefly.
