When most people think of fire-resistant materials, sawdust is probably one of the last things to come to mind. Scientists have now used it in such a substance, however, along with the plentiful mineral that kidney stones are made of.
The mineral, known as struvite, is a crystalline, colorless ammonium magnesium phosphate that has long been known for its flame-retardant qualities. It's brittle on its own, however, needing to be mixed with some other material to give it strength.
That's where the sawdust comes in. Generated as forestry and lumber industry waste, sawdust is typically either burned for energy or simply dumped in landfills.
Past efforts have been made to combine it with struvite, in order to form fire-resistant panels that could be used for internal partitions within buildings. The problem has been, the manner in which struvite crystallizes has kept it from bonding well with sawdust.
Researchers from Switzerland's ETH Zurich and Empa universities, working with colleagues from the Polytechnic University of Turin, have now solved that problem.
Utilizing an enzyme derived from watermelon seeds, the scientists were able to to control the manner in which struvite crystallizes from an aqueous suspension of a mineral precursor called newberyite. This resulted in large crystals that filled all the cavities between spruce sawdust particles, binding all of them firmly together.
Slabs of the resulting material were pressed in a mould for two days, after which they were removed and dried at room temperature. When strength-tested, the panels were found to be stronger under compression perpendicular to the grain than the original spruce timber.
The material also exhibited excellent fire resistance, thanks to the struvite. When the mineral is heated, it reacts by breaking down and releasing water vapor and ammonia.
As part of that process, the struvite absorbs heats from the surrounding environment, producing a cooling effect. It also releases non-combustible gases that displace air, thus starving the fire and keeping it from spreading, while causing the panel to char quicker and become less flammable.
Initial testing indicates that the panels should offer the same level of fire protection as existing cement-bonded particleboards, yet at a much lighter weight.
Additionally, whereas cement boards are typically just discarded when removed from demolished buildings, the struvite panels could be recycled. Doing so would involve grinding them up, heating the material to 100 ºC (212 ºF), then sifting out the sawdust and precipitating out the newberyite for reuse.
A paper on the study, which was led by ETH Zurich doctoral researcher Ronny Kürsteiner, was recently published in the journal Chem Circularity.
Source: ETH Zurich
