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When we think of knives we usually picture steel or ceramic, but researchers have developed a way to make strong knives from wood. The material in question is called hardened wood. Material scientists have found a way to make wood 23 times harder and then turned it into a knife that is three times sharper than a stainless-steel dinner table knife.
The method and results are published in the journal Matter. Compared to the production approach for both steel and ceramic, hardened wood knives are likely to be a lot more sustainable. And they can be washed and reused just like regular knives.
“The knife cuts through a medium-well done steak easily, with similar performance to a dinner table knife,” senior author Teng Li, from the University of Maryland, said in a statement.
But it’s not just cutlery. Hardened wood could be employed in other types of objects where iron and steel are commonly used. One example tested by the team is nails. The team nailed three planks of wood together without the nail getting duller in the process.
The starting point for this work was the team recognizing that human-made materials often satisfy needs that natural-based materials cannot. Even though they might have the potential to do so if treated the right way.
“Cellulose, the main component of wood, has a higher ratio of strength to density than most engineered materials, like ceramics, metals, and polymers, but our existing usage of wood barely touches its full potential,” Li explained.
Wood is between 40 to 50 percent cellulose, but the remaining components, hemicellulose and lignin, are weaker. The hardened wood process removes these components and makes the material live up to its full potential.
“It’s a two-step process,” said Li. “In the first step, we partially delignify wood. Typically, wood is very rigid, but after removal of the lignin, it becomes soft, flexible, and somewhat squishy. In the second step, we do a hot press by applying pressure and heat to the chemically processed wood to densify and remove the water.”
The process removes natural defects found in wood, making it stronger. It can then be shaped into whatever shape is desired.
The team is investigating how often the chemicals used in the processing can be reused and just how much energy is needed, so they can assess the environmental impact of this method compared to traditional ones.
“In our kitchen, we have many wood pieces that we use for a very long time, like a cutting board, chopsticks, or a rolling pin,” said Li. “These knives, too, can be used many times if you resurface them, sharpen them, and perform the same regular upkeep.”
