Most good knives are made of steel or ceramic, but researchers have now developed a method for creating incredibly tough knives from wood. A technique reported in the journal Matter can make wood 23 times harder than it is to start with, and when knives are made from this material, tests indicated that they're three times sharper than table knives made of stainless steel. These wooden knives can be washed and reused, and they easily cut through a steak cooked medium well, said senior study author and materials scientist Teng Li.
Cellulose is one of the world's most common materials. It's the primary component of wood, and it has the potential to be stronger than ceramics, metals, or polymers, but we are not using wood to its full potential, said Li, a Keystone Professor and Director of the Laboratory for Advanced Sustainable Materials and Technology (LASMAT) at the University of Maryland, College Park.
Wood is not as strong as cellulose, because it contains other binders, like lignin. Li and colleagues set out to eliminate some of the weaker parts of wood while retaining the cellulose structure.
"It's a two-step process," Li explained. "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." The first step is conducted at 100 degrees Celsius in a chemical bath, while ceramics have to be heated to thousands of degrees Celsius. This manufacturing process may have a lower environmental cost than the production of other materials, but more work will be needed to confirm that hypothesis.
"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," Li continued. Once this process is complete, the resulting wood is coated with mineral oil to reduce the likelihood that the cellulose will absorb water, extending the longevity of the piece.
The researchers also made nails from this hard wood, and they're just as sharp as steel nails, but they are not vulnerable to rust.
"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," noted Li. "These knives, too, can be used many times if you resurface them, sharpen them, and perform the same regular upkeep."
Sources: Cell Press, Matter
