When two pieces of wood treated in this way are brought together, the non fibrils bind to create what the researchers call a “healed” piece of wood. Although this no longer looks like natural wood, it has better mechanical properties. Tests show it is more resistant to breaking than stainless steel or titanium alloys.
“We get a mechanical strength that supersedes the strength of the original material,” says Rojas. It works because we use the inherent properties of cellulose, which is a material that binds together very strongly by something called hydrogen bonding.
Not only can wood treated this way be re-used to create new objects, but the treatment process can be performed repeatedly on the same pieces of wood to extend their working lifetimes.
“This is a really elegant way to heal wood, using a common cellulose solvent, recovering and enhancing the mechanical properties of nature’s wonder material,” says Steve Eichhorn at the University of Bristol, UK. “The approach is evidently scalable, and therein lies the challenge to take this technology to the next level.”
Rojas and his team didn’t examine how much their method would cost if scaled up to an industrial level, but all the techniques used are well-established. “The processes that we use here are very typical in wood processing,” says Rojas.
Wooden knives that are three times sharper than steel ones could help cut energy use and plastic cutlery waste.
Ten at the University of Maryland and his colleagues developed a material called hardened wood, which is 23 times harder than raw wood and can be carved to make knives three times sharper than standard steel ones. A coating of mineral oil makes the knives resistant to water.
“The hardened wood knives can be washed, dried and resharpened if needed, so that an extended lifetime is expected,” says Ten.
The key to making the knives, so sharp was using strong cellulose fibers found in plant cell walls, which make up almost half the mass of wood, rather than weaker polymers in cell walls called lignin and hemicellulose.
The team removed these weaker polymers from raw wood by soaking it in a solution containing sodium hydroxide and sodium sulfate, before boiling the solution at 100 °C for a few hours. They then squished the remaining cellulose fibers together at a pressure of 20 megapascals for 6 hours before drying them at around 100 °C to produce hardened wood.
Making commercially available steel and ceramic knives often requires at least 10 times higher temperatures and pressures, making these wooden knives a less energy intensive form of cutlery.
The team compared the sharpness of knives made from hardened wood with those made from steel by measuring how easily the blades sliced through a standard electrical wire. They found that the wooden knives required around three times less force to slice through the wire compared with steel knives.
The team found that the wooden knives felt comparable with steel knives when cutting through medium-well done steaks.
“There are more than 3 trillion mature trees on Earth. They are abundant and renewable. Revealing and realizing the full potential of wood, beyond its conventional use, holds promise towards a better and greener future. We’d love to see its commercialization in the near future,” says Tenn.
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