The knife should be sharp, solid, and should not break too quickly. With such specifications, you quickly end up with a steel or ceramic knife. Plastic knives score poorly on all three points. And the wooden spoons you get in some canteens don’t have to be called a knife. The wood is very soft and prone to such applications.
That verdict was not quick, US materials scientists claimed this week in the trade journal Matter. They describe a method for hardening wood – up to 23 times its natural hardness. Their wooden blade went three times smoother A piece of meat Like an ordinary table knife.
Wood is made up of about half of cellulose. These are long chains of sugar molecules, which together form the fibers and give wood its solid structure. Strength is enhanced by hemicellulose, which also consists of chains of (other) sugar molecules wrapped around cellulose. Finally, there’s lignin, which is the kind of glue that holds everything together.
The weakness of wood lies in the space between these fibers. The tree needs that space to transport moisture and food. But they are also places where wood can break.
Early in 2018, Teng Li and colleagues at the University of Maryland showed how to fix this weakness. in the magazine temper nature They described their two-stage method. At first they immersed the wood in a boiling water bath with chemicals – including caustic soda. As a result, part of the lignin and half of the cellulose were extracted from the wood. What they’re left with, in their own words, is “soft, bendable, and somewhat spongy” wood. Then they squeezed the water out under high pressure, after which they had a log that occupies only a fifth of its original volume.
It has already been shown that pressed wood has wonderful properties. It was scratch and break resistant. He easily stopped the bullet while penetrating an equally thick plank of natural wood.
In the years that followed, they went looking for applications for their hardwoods and so came up with the knives. They write that the manufacture of stainless steel or ceramic blades is not at all sustainable. Requires ovens to be heated to a few thousand temperatures. And certainly ceramic materials, usually such as zirconia, are not reusable. In comparison, a hundred-degree chemical bath temperature is more environmentally friendly. And the chemicals themselves are reusable many times.
In their article in the journal Matter, the researchers describe what it takes to make a wooden knife. The cutting edge should be in the direction of the wood grain – otherwise the blade will dull quickly – and the blades should be immersed in an oil bath to prevent them from swelling after each wash. But then you also have a sustainable and cheap alternative to steel knives, they deduced from all kinds of tests they did with knives.
The knife is not the only application of hardened wood. The Americans also made nails out of it that they put in demonstration By means of three plates. Doesn’t rust, give it an extra recommendation. Wood may one day be used for wear-resistant floors.
It is interesting, says Peter Deuss, who studies the properties of biomaterials at the University of Groningen. “They show really well that you can do more with wood than you first thought.” The micrographs that come with the article also give him the conviction that the blades of hardwood are sharp. “But not as sharp as some ceramic knives.”
His concerns are mainly in large-scale applications. Now they’ve done it all with lemon wood. Do you also work with other woods? Presumably yes, but with a slightly different treatment. After all, each type of wood has its own fibrous structure. Sounds good, but once you start producing those knives in high-volume operations, you can always run into unexpected effects. “This is especially true for sustainability. How do the blades stay waterproof, how do the nails last?” I read as a recommendation that the wood is biodegradable. This doesn’t look quite right on the nails.”
Lee understands that you have to handle knives carefully. If they stay in the water for 24 hours, there won’t be much sharpness left. “But that goes for all things wood in the kitchen,” he says in a press release from his university. “You also have to properly maintain your wooden cutting board or rolling pin.”
However, Deuce says, wood is a sustainable material, and Maryland researchers aren’t the only ones pursuing new manufacturing techniques. “There was a recent publication on translucent wood. Usually it still has to prove itself, but all kinds of application possibilities are emerging.”
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