Researchers make hardened wooden knives that slice through steak

Date:
October 20, 2021
Source:
Cell Press
Summary:
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 makes wood 23 times harder and a
knife made from the material is nearly three times sharper than
a stainless-steel dinner table knife.



FULL STORY ==========================================================================
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 100DEG 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." ========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Chen et al. Hardened Wood as a Renewable Alternative to Steel and
Plastic. Matter, 2021 DOI: 10.1016/j.matt.2021.09.020 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211020135928.htm

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