Researchers make hardened wooden knives that slice through steak
From: Cell Press
October 20. 2021 -- The sharpest knives
available are made of either steel or ceramic, both of which are human-made
materials that must be forged in furnaces under extreme temperatures. Now,
researchers have developed a potentially more sustainable way to make sharp
knives: using hardened wood. The method, presented October 20th in
the journal Matter, makes wood 23 times harder, and a knife made
from the material is nearly three times sharper than a stainless-steel dinner
table knife.
"The knife cuts through a
medium-well done steak easily, with similar performance to a dinner table
knife," says Teng Li (@ToLiTeng), the senior author of the study and a
materials scientist at the University of Maryland. Afterwards, the hardened
wood knife can be washed and reused, making it a promising alternative to
steel, ceramic, and disposable plastic knives.
Li and his team also demonstrated that
their material can be used to produce wooden nails as sharp as conventional
steel nails. Unlike steel nails, the wooden nails the team developed are
resistant to rusting. The researchers showed that these wooden nails could be
used to hammer together three boards without any damage to the nail. In
addition to knives and nails, Li hopes that, in the future, the material can
also be used to make hardwood flooring that is more resistant to scratching and
wear.
While Li's method to produce hardened
wood is new, wood processing in general has been around for centuries. However,
when wood is prepared for furniture or building materials, it is only processed
with steam and compression, and the material rebounds somewhat after shaping.
"When you look around at the hard materials you use in your daily life,
you see many of them are human-made materials because natural materials won't
necessarily satisfy what we need," says Li.
"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," he says. Even though it's often used in
building, wood's strength falls short of that of cellulose. This is because
wood is made up of only 40%-50% cellulose, with the rest consisting of
hemicellulose and lignin, which acts as a binder.
Li and his team sought to process wood in
such a way to remove the weaker components while not destroying the cellulose
skeleton. "It's a two-step process," says 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."
After the material is processed and
carved into the desired shape, it is coated in mineral oil to extend its
lifetime. Cellulose tends to absorb water, so this coating preserves the
knife's sharpness during use and when it is washed in the sink or dishwasher.
Using high-resolution microscopy, Li and
his team examined the microstructure of the hardened wood to determine the
origin of its strength. "The strength of a piece of material is very
sensitive to the size and density of defects, like voids, channels, or
pits," says Li. "The two-step process we are using to process the natural
wood significantly reduces or removes the defects in natural wood, so those
channels to transport water or other nutrients in the tree are almost
gone."
This wood-hardening process has the
potential to be more energy efficient and have a lower environmental impact than
for the manufacture of other human-made materials, although more in-depth
analysis is necessary to say for sure. The first step requires boiling the wood
at 100° Celsius in a bath of chemicals, which could potentially be reused from
batch to batch. For comparison, the process used to make ceramics requires
heating materials up to a few thousand degrees Celsius.
"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," says Li. "These knives, too, can be used many times if
you resurface them, sharpen them, and perform the same regular upkeep."
Journal Reference:
- Chen
et al. Hardened Wood as a Renewable Alternative to Steel and
Plastic. Matter, 2021 DOI: 10.1016/j.matt.2021.09.020
https://www.sciencedaily.com/releases/2021/10/211020135928.htm
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