New process to harden wood

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Vigilant1

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TFF

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I have a feeling that this is going to make super duper partial board not strengthening lumber. They dance around the question of is it a chunk of wood or is it sawdust.
 

rv7charlie

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Healthy skepticism is healthy, but in this case, I doubt that they're talking about particle board (compressed sawdust). Articles about high strength wood construction products made with similar sounding processes have been floating around the non-aviation sites for several years; more in Europe than here in the USA. IIRC, there are already some large structures being built using it instead of steel structural members; not something a local permitting dept is likely to allow with particle board.
 

wsimpso1

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Let me get this straight:
  • Start with wood which is hollow fibers of cellulose bonded together with a resin called lignin;
  • Dissolve out most of the lignin with a solvent, which becomes a waste stream, probably best disposed of by using as fuel in a heating plant;
  • Compress most of the free space out of the cellulose under both heat and pressure so that the remaining lignin bonds it back together.
And this is supposed to make a material of higher specific strength and stiffness than metals?

We do a similar process to make nitrocellulose:
  • Wash the resins from the cellulose;
  • Wash it in nitric acid to add a nitrogen atom to each free end along the molecule - there are a lot of them along cellulose;
  • Colloid it with a mix of ethanol and acetone (makes a homogenous jelly of it);
  • Extrude it into any desire shape is desired - it is usually extruded into strands that look like pasta, cut the strands into little flakes, cylinders, etc;
  • Dry the solvents back out of it.
This is gunpowder process, and the stuff is hardly strong or very tough. Now maybe leaving the fiber structure while collapsing the air space out of it will help some, and leaving some lignin to hold the now dense cellulose fibers together will help some, but it sounds like $10-20 a pound material given the similarities of processing. And you end up with a material with variability in strength and stiffness depending up variation in the raw materials you are starting with, with max size restrictions - no part can be longer than the raw wood piece you start with, and will always be smaller in cross section.

Another restriction upon this densified wood is that it is still a highly directional material. The high tensile strength and modulus some are claiming is along the direction of the fibers. What does it do in compression? Kevlar has low compression strength along the fibers because it micro-buckles, and I expect similar behaviour here. Across the fibers in tension, this stuff will still have a modulus and strength reflecting the behavior of lignin, which is low. I imagine it will be more like Kevlar than like metal, have to be applied as strands like composites, and be bonded up to make parts like composites too.

Seems like very uniform fibers made of glass or graphite are way more appealing if we are looking to make high tech structures. We shall see if usable material comes from this work, but I am not holding my breath over it.

Billski
 

Vigilant1

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I know it's not the most reliable source of scientific info....
Yeah, ya got that right. From the article:

"Waugh Thistleton estimates that the wood in Stadthaus stores 186 tons of carbon while the steel and concrete for a similar, conventionally built tower would have generated 137 tons of carbon dioxide during production. Wood nets a savings of 323 tons."

Nope. Carbon dioxide isn't the same as carbon. If a steel and concrete building would have produced 137 tons of CO2, that's just 37 tons of carbon.
And the steel can be recycled and used again and again, the carbon footprint for that is much lower than virgin steel from ore. No word on how the chemically altered "wood" will be disposed of. Microbial decay or burning will put much of the carbon back into the atmosphere.
 
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