Hardened Wood Knife Can Slice a Steak More Easily Than Steel

Our days of pointlessly pawing at a stubborn salad with flimsy plastic cutlery may be numbered, as researchers report the invention of a wood-hardening technique that can produce cutlery 23 times tougher than conventional wood.

The research team, based at the University of Maryland, were led by senior author Teng Li. Noting that conventional cutlery is made using high-energy processes, Li’s team looked to naturally available materials for an alternative.

“When you look around at the hard materials you use in your daily life, you see many of them are man-made materials because natural materials won’t necessarily satisfy what we need,” said Li in a press release. Anyone who has used a regular wooden knife can attest that they aren’t the most efficient implements. But Li’s new hardened knife is a different beast, forged in a two-step process.

Breaking the matrix

The team started with regular basswood, a tree native to the Eastern US that produces soft, light-brown wood. The presence of the biopolymer lignin is a significant obstacle to hardening as it forms a matrix that lines plant cell walls, reducing the wood's strength. The team first bathed the basswood in a chemical mixture that broke down the lignin and then compressed the wood at room temperature, crushing the innumerable fibers and pores that run through the raw wood and removing any residual water.

A final run through a hot press then further compacts the wood, creating a hardened block that, once dry, has a Brinell hardness number of 31.21, which is 23 times that of natural basswood. The process also avoids using the energy-guzzling, high-temperature processes required to create ceramic and steel products.

Scanning electron microscopy analysis of the wood confirmed the reasons for its strength. “The strength of a piece of material is very sensitive to the size and density of defects, like voids, channels, or pits,” said 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.”

While the resulting product may be significantly softer than stainless steel, the hardened wooden knife, especially when carved so that the wood fiber is perpendicular to the direction of the blade, proved sharper than commercial steel or regular wooden knives. This was measured by cutting through a polymer wire while calculating the force at which the wire severs. When the knife was sawed back and forth on the wire, 0.75 kg of force was required to cut it, while a steel table knife needed 1.77 kg of force.

To demonstrate the power of their knife with a less abstract test, the team served up a medium-rare steak and cut through it with their knife, as seen in the video below.

Researcher cutting a steak with a hardened wood knife. Credit: Bo Chen

Nailing the problem of rusty metal

The team also recognized that man-made metals are vulnerable to decay. The rusting of steel nails is a good example, and the team created a hardened wood nail that was able to pound together three basswood planks. The force required to break through the planks was roughly comparable to that of a steel nail.

Of course, wooden implements have their own vulnerabilities to decay, so the team additionally treated their hardened wood with a food-grade mineral oil that was able to substantially increase the wood’s water-resistance. Nonetheless, the knife’s hardness number decreased from above 30 to less than 20 after 24h soaking in water – the knife’s long-term integrity, especially when being regularly washed, has yet to be established.

Li, however, indicated that, like other wooden implements, a bit of a care could see hardened wooden knives endure: ““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. These knives, too, can be used many times if you resurface them, sharpen them, and perform the same regular upkeep.”

Reference:

Chen, B, Leiste, U, Fourney, WL, Liu, Y, Chen, Q and Li, T. Hardened wood as a renewable alternative to