Super wood! Windows and knives from wood

Material scientists are giving wood super properties; transparent for windows, and extra hard for knives.
23 November 2021

Interview with 

Teng Li, University of Maryland


Tree rings indicate the age of a tree in years


It sounds like we can build our flats from wood, paint the walls shiny colours with wood, all we need now are wooden windows and wooden cutlery. Which sounds a bit far fetched, but these have already been invented. Sally Le Page spoke with Teng Li, a mechanical engineer from the University of Maryland.

Sally - So how do you make wood transparent?

Tang - It actually has two steps over there. The first step is more chemical processing. You bleach the wood and then the wood it penetrated is the synthetic polymer, the resulting piece of wood is actually virtually transparent.

Sally - Amazing! And why do you want to make wood transparent? What's wrong with glass?

Tang - We have been using glass for many, many years in the windows and other applications, but glass has several disadvantages. For example, we know that the glass is very brittle. It can be easily shattered into sharp pieces. By contrast the transparent wood is much tougher than glass. Also the glass production in construction comes with a heavy carbon footprint, by contrast transparent wood is made from a sustainable and renewable resource with low carbon emissions and also has a better thermal efficiency.

Sally - So even with all of that bleaching and the resins you need to add, it's still better for the environment than glass.

Tang - Hopefully I think it has a very good potential in the future as a potential replacement for glass.

Sally - And you say it’s a potential in the future. How big are the pieces that we've got already? Is anyone making windows out of transparent wood yet?

Tang - Not yet. So far, I believe this is done at the lab scale, but the process I mentioned can be scalable to an industrial scale when it's getting to the commercialization stage.

Sally - Incredible. I can't wait to see it. I hear in your lab Tang, you have made a steak knife out of wood. What on earth gave you that idea?

Tang - Yeah. We have been working on exploring the new usage of wood. We have this process to make the wood 23 times hotter than the natural wood. Then we were scratching our heads to find a potential application of this and we realized that actually we use harder materials a lot in our daily life. For example dinner table knives, typically we use a stainless steel one and at parties we use the plastic ones. We were trying to make a super hard wood knife. It turns out that it's actually quite sharp, it's actually sharper than the typical dinner table knives we use.

Sally - Wait, a wooden knife is sharper than a steel knife?

Tang - Yeah. We measured the cutting force of the super hard wood knife and compared with the cutting force of typical dinner table knives made of stainless steel or natural wood or plastic ones, it turns out that the super hardwood knife has a smaller carding force.

Sally - I would never have believed that. What do you have to do to the wood to make it so hard?

Tang - It evolves in two steps. The first step is chemical processing as you mentioned in the earlier of today's program. We partially remove one of the components in wood, which is the lignin. In the second step, you can really densify the wood into a piece of material, which is much hotter than the natural wood.

Sally - When you've got your wooden knife, can you still stick it in the dishwasher?

Tang - Oh yeah, indeed. If you look around our kitchen, we have been using wood utensils, cutting boards, spoons, chopsticks, and they can be used multiple times. You can wash it in the dishwasher. It survives the usage over a long time and the durability of the super hardwood is actually better than the natural wood so we expect that this can be used for even longer time.

Sally - Amazing. I'm one of those people who buys cheap knives and they go blunt immediately. So it sounds like your wood one might actually be better. And then you've also been working on super strong wood. Can you tell me a bit more about that?

Tang - Yeah. So using the same process, you can make the natural wood more than 10x stronger than the original material. Also the resulting super strong wood is more light-weighted. For example, the strength of that super strong wood is comparable or even higher than some of the steels, but the density is six times lighter, which means that you are getting a piece of material, which is comparable to steel, but it's more light-weighted. So it actually leads to a lot of potential as a replacement for steel.


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