Natural wood and metal have been essential building materials for humans for thousands of years.The synthetic polymers we call plastics are a recent invention that exploded in the 20th century.
Both metals and plastics have properties that are well suited for industrial and commercial use.Metals are strong, rigid, and generally resilient to air, water, heat, and constant stress.However, they also require more resources (which means more expensive) to produce and refine their products.Plastic provides some of the functions of metal while requiring less mass and is very cheap to produce.Their properties can be customized for almost any use.However, cheap commercial plastics make terrible structural materials: plastic appliances are not a good thing, and no one wants to live in a plastic house.Additionally, they are often refined from fossil fuels.
In some applications, natural wood can compete with metals and plastics.Most family homes are built on wood framing.The problem is that natural wood is too soft and too easily damaged by water to replace plastic and metal most of the time.A recent paper published in the journal Matter explores the creation of a hardened wood material that overcomes these limitations.This research culminated in the creation of wooden knives and nails.How good is the wooden knife and will you use it any time soon?
The fibrous structure of wood consists of approximately 50% cellulose, a natural polymer with theoretically good strength properties.The remaining half of the wooden structure is mainly lignin and hemicellulose.While cellulose forms long, tough fibers that provide wood with the backbone of its natural strength, hemicellulose has little coherent structure and thus contributes nothing to the wood’s strength.Lignin fills the voids between cellulose fibers and performs useful tasks for living wood.But for humans’ purpose of compacting wood and binding its cellulose fibers more tightly together, lignin became a hindrance.
In this study, natural wood was made into hardened wood (HW) in four steps.First, the wood is boiled in sodium hydroxide and sodium sulfate to remove some of the hemicellulose and lignin.After this chemical treatment, the wood becomes denser by pressing it in a press for several hours at room temperature.This reduces the natural gaps or pores in the wood and enhances the chemical bonding between adjacent cellulose fibers.Next, the wood is pressurized at 105° C (221° F) for a few more hours to complete densification, and then dried.Finally, the wood is immersed in mineral oil for 48 hours to make the finished product waterproof.
One mechanical property of a structural material is indentation hardness, which is a measure of its ability to resist deformation when squeezed by force.Diamond is harder than steel, harder than gold, harder than wood, and harder than packing foam.Among the many engineering tests used to determine hardness, such as the Mohs hardness used in gemology, the Brinell test is one of them.Its concept is simple: a hard metal ball bearing is pressed into the test surface with a certain force.Measure the diameter of the circular indentation created by the ball.The Brinell hardness value is calculated using a mathematical formula; roughly speaking, the larger the hole the ball hits, the softer the material.In this test, HW is 23 times harder than natural wood.
Most untreated natural wood will absorb water.This can expand the wood and eventually destroy its structural properties.The authors used a two-day mineral soak to increase the water resistance of the HW, making it more hydrophobic (“afraid of water”).The hydrophobicity test involves placing a drop of water on a surface.The more hydrophobic the surface, the more spherical the water droplets become.A hydrophilic (“water-loving”) surface, on the other hand, spreads the droplets flat (and subsequently absorbs water more easily).Therefore, mineral soaking not only significantly increases the hydrophobicity of the HW, but also prevents the wood from absorbing moisture.
In some engineering tests, HW knives performed slightly better than metal knives.The authors claim that the HW knife is about three times as sharp as a commercially available knife.However, there is a caveat to this interesting result.Researchers are comparing table knives, or what we might call butter knives.These are not meant to be particularly sharp.The authors show a video of their knife cutting a steak, but a reasonably strong adult could probably cut the same steak with the dull side of a metal fork, and a steak knife would work much better.
What about the nails?A single HW nail can apparently be easily hammered into a stack of three planks, although not as detailed as it is relative ease compared to iron nails.Wooden pegs can then hold the planks together, resisting the force that would tear them apart, with about the same toughness as iron pegs.In their tests, however, the boards in both cases failed before either nail failed, so the stronger nails were not exposed.
Are HW nails better in other ways?Wooden pegs are lighter, but the weight of the structure is not primarily driven by the mass of the pegs that hold it together.Wooden pegs will not rust.However, it will not be impervious to water or biodecompose.
There is no doubt that the author has developed a process to make wood stronger than natural wood.However, the utility of hardware for any particular job requires further study.Can it be as cheap and resource-less as plastic?Can it compete with stronger, more attractive, infinitely reusable metal objects?Their research raises interesting questions.Ongoing engineering (and ultimately the market) will answer them.
Post time: Apr-13-2022
