Wood-based supermaterial is stronger and tougher than steel

Saturday, January 5th, 2019

A new wood-based supermaterial is stronger and tougher than steel:

In their natural form, wood cells are kept rigid due to polymers known as lignin and hemicellulose, interspersed with nanofibres of cellulose. Wood also contains systems of narrow tubes known as lumina, which run along its growth direction. To transform this structure into a more useful material, Hu’s team first treat samples of wood with a salt solution, which removes most of the lignin and hemicellulose, making the cell walls porous and less rigid. Afterwards, the researchers hot-press the wood at 100 °C, causing the cell walls and the lumina to collapse. This reduces the wood to just 20% of its original thickness.

The compressed substance contains densely-packed wood cells aligned along the growth direction, which results in a strongly-aligned system of cellulose nanofibres. These fibres have hydrogen and oxide groups in their molecular structures, giving rise to strong hydrogen-bond interactions between them. The density of the new material is about three times higher than that of untreated wood.

Once they had perfected the conversion process, Hu’s team set about testing the properties of their new substance. In most structural materials there is a trade-off between tensile strength (resistance to breaking while being stretched) and toughness (how much energy a material can absorb without shattering) — but the researchers saw improvements in both properties in their new material. Its tensile strength is 11.5 times higher than that of natural wood, making it much stronger than common plastics such as nylon and polystyrene. However, the toughness of the new material is also boosted — it is 8.3 times higher than natural wood, making it tougher than most metal alloys.

(Hat tip to Hans Schantz.)

Comments

  1. Handle says:

    And trees are already pretty tough as is. In this video he’s shooting at softwood pine and it still stops almost all small arms.

    https://www.youtube.com/watch?v=KZgzuso-wCU

  2. Candide III says:

    Lol, the guy in the video reminds me very much of Tank from the first Matrix movie.

  3. Slovenian Guest says:

    Were you thinking what i was thinking?

    Pykrete 2.0!

  4. Gaikokumaniakku says:

    Does it rot when it gets wet? Can termites eat it?

  5. Bob Sykes says:

    What keeps wood in anaerobic environments is the lignin, which requires oxygen to initiate the biodegradation. Since this product is nearly pure cellulose, which bacteria can degrade readily in almost any environment, I should think this product is potentially biodegradable, too. However, the dense packing of the cellulose fibers might decrease their availability to enzymes.

    Another question is, how workable is the material? Wood itself is easily worked and shaped, although joining pieces is a nuisance.

  6. Buckethead says:

    My son and I made some of this last spring. We got the original paper from the University of MD scientists and boiled us up some wood. We used a shop press and some metal plates to compress it.

    Our first effort came out best. We figured out the issue we had with our later batches was that the solution got too strong. We didn’t add enough water as it boiled down. The resulting material was compressed, but not uniformly strong.

    I made a knife out of the first batch. It holds a decent edge, considering it was originally wood.

    We had to leave off working on it, but we’re planning to make more in a month or two. I’m going to get a bigger shop press and modify it to apply a more even pressure over a wider area. Should work pretty well. Takes about a day to boil the wood, and overnight to cure it.

  7. Aretae says:

    Nice.

    Wooden steel knife?

  8. Graham says:

    I’m ill-equipped to evaluate this sort of thing but I must say materials science is one of the areas of science and engineering which keeps astounding me and so far as I can tell to date has produced no reservations in me. So, woohoo. This sort of thing is good news.

  9. buckethead says:

    Bob, the material is pretty workable, though it’s a bit more like working metal. Maybe 80% of the way from working normal wood to steel. I used an angle grinder to shape the knife from the one small piece of viable material we got out of our first batch, and then sandpaper to put a fine edge on it. Sandpaper worked, but slowly. Not sure how easy to drill it will be.

    Joining it isn’t something we got to, though we will next time around. From what we read, you can press pieces together to form cross-grained densified plywood that is even stronger. We didn’t get the opportunity to play with that, but that’s also on the list.

    The knife I made has a small tang, and I haven’t put a handle on it. The shape of the blade is vaguely tanto-like, mostly because that’s what fit the amount of material we had rather than any real aesthetic decision.

    Completely invisible to metal detectors, and it looks rather nice. I’m looking forward to making better quality material soon, and see if I can make an even better one.

  10. Sam J. says:

    Another interesting wood product is the stuff lined below. It’s incredibly strong and it provides a lot of the strength of wood. There was a lot of talk about using it to reinforce plastics. It’s one of those things that I bet will slowly creep in as it provides something very strong potentially very cheaply.

    https://en.wikipedia.org/wiki/Nanocellulose

    “…Crystalline cellulose has interesting mechanical properties for use in material applications. Its tensile strength is about 500MPa[citation needed], similar to that of aluminium. Its stiffness is about 140–220 GPa, comparable with that of Kevlar and better than that of glass fiber, both of which are used commercially to reinforce plastics. Films made from nanocellulose have high strength (over 200 MPa), high stiffness (around 20 GPa)[22] and high strain[clarification needed] (12%). Its strength/weight ratio is 8 times that of stainless steel.[23] Fibers made from nanocellulose have high strength (up to 1.57 GPa) and stiffness (up to 86 GPa).[24]..”

    If you want to get a good reading on how exactly strong something is this is the keyword. Tensile strength just tells you by area. The real test is strength per weight(strength/weight ratio). Nice chart of some average, and not so average, materials in the link.

    https://en.wikipedia.org/wiki/Specific_strength

    A great, really great, book on this is,”Structures: Or Why Things Don’t Fall Down” by J. E. Gordon

    Also covering much the same material is,”The New Science of Strong Materials: Or Why You Don’t Fall through the Floor” (Princeton Science Library) J. E. Gordon

    Easy to read and lots of entertaining examples.

Leave a Reply