New plant-derived composite is tough as bone and hard as aluminum | Hacker News Reader

New plant-derived composite is tough as bone and hard as aluminum

news.mit.edu

142 pointsjonbaer80 comments

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It sounds cool, but then this:

> a composite made mostly from cellulose nanocrystals mixed with a bit of synthetic polymer

So it still contains non-degradable plastic, just less plastic than before.

There have been a spate of such articles recently, where "less plastic" is pitched as "no plastic".

I'm not saying it's bad, but it's not as good as it appears.

The subtitle effectively says 'new plastics'. I don't think it is trying to pitch 'no plastic'.

We don't know which polymer it is, nor how or what it's synthesized from. PLA is synthesized for example, just not from petrochemicals.

Being non-biodegradable is a pretty important feature for anything that has to interact with the elements. A house constructed out of truly biodegradable materials would be a disaster.

Well, FSVO "disaster". Wood is biodegradable, and a house made entirely out of wood (say a log cabin) might last only 50 years, but that's plenty of time on human scales of habitability.

In actual, no context terms I agree that a home Meade from wood doesn’t biodegrade fast enough on human scales. However, Infeel like the externals associated with the cultural concepts, particular in ‘the west’, around real property and houses as investments (either for rent or for future descendents) make this statement not accurate in a practical way. So, I don’t think it stands as an argument against excluding non-biodegradable materials in construction projects.

European half-timbered houses are out of what then? They're still standing strong, being around 700 years old. Or how about the stairway in Hallstatt? Or the wooden house Kirkjubøargarður? Is wood not truly biodegradable? I think I know what you might mean, but it's not as black and white as you make it to be.

Wood are certainly biodegradable, and some takes a long time to degrade. Afaik many wood houses use paintings or coatings to protect from nature (at least where I live). So, I wonder if it applies to European half-timbered house.

Agreed. But you can also smoke the wood a bit, helps with the weather. Also the interconnectedness is something that helps I think. Because you reduce the surface.

I would expect something that was biodegradable to biodegrade in less than 700 years. If you have that sort of time, plastics are sort of biodegradable as well.

Are you listening to yourself? Are you really trying to say that wood is not biodegradable? Lolwut

Being biodegradable doesn't mean that it will degrade in any circumstances. Lumber in a house is usually protected from many biological degradation agents, even if it is not chemically treated. If you took that same wood and threw it in a pile exposed to rain and bugs, it would be gone in less than 100 years.

Could part of that be explained by the use of old growth wood? My understanding is it's much more robust than modern wood.

I live much closer to the tropics, how big of a problem are termites in Europe?

I don't think it's a problem at all, never heard about that to be honest.

Aren't those treated with varnishes and oil to prevent it from degrading?

My experiences with exterior varnish (terrible) and oil (marginal at best) would suggest that design is very important.

Eves to protect cladding are essential and if you get a lot of wind and sun, very wide eves.

A combo of UV and rain just punishes wood, and oil/varnish doesn’t handle it well.

Paint fares a lot better.

All biodegradable materials don't degrade the same in every condition. For example, both cedar timber and romaine lettuce are biodegradable, but you wouldn't coat your exterior walls in romaine lettuce. But if I buried both in humid soil and waited 10 years before digging them back up, I'd likely see no sign of either.

Most plastics are not biodegradable. They don't degrade in any condition. If I buried a fidget spinner and waited 10, 100, or 1,000 years, It'd still likely find most of a fidget spinner when I dug it up.

Cellulose nanocrystals (CNCs) have been around for awhile now just like how we have had carbon nanotubes (CNTs) and graphene.

These nanoparticles offer really a interesting strength to weight ratio and a relatively easily modified surface compared to CNTs. The article posted here is misleading due to the relatively high cost of the CNCs to isolate and then use in what looks to be an under cured epoxy resin.

Isolating the CNCs potentially can be done through mechanical means, but I suspect the authors here were using chemical isolation through some sort of acid hydrolysis (they don't say in the abstract).

But overall mixing the CNCs at that weight ratio with an epoxy resin should have yielded 1-3 GPa modulus or higher and the fact that they got 0.66 to me indicates it's under cured and not really that useful.

I actually worked on this stuff when I was in graduate school and we were doing surface modified CNCs with a biobased epoxy resin. We loaded at 1-10 wt% of CNCs and got modulus values between 2-3 GPa with some modest increases in Tg. We were expecting better results, but that's life.

This to me seems like MIT is trying to toot their own horn for some not very interesting results.

Ok, so this sounds like a cellulose/resin composite (compare to carbon fibre).

Based on https://link.springer.com/article/10.1007/s10570-021-04384-7 (the summary of the source article), it is substantially weaker than carbon fibre. Fracture toughness is afaict ~50MPa^1/2 vs 5.2. The article reports hardness of 0.66GPa, but from the summary I don't know by which modulus, however carbon fibre is stronger than that in all measures.

>“We basically deconstructed wood, and reconstructed it,” Rao says. “We took the best components of wood, which is cellulose nanocrystals, and reconstructed them to achieve a new composite material.”

Potential for Construction material? As with all these discover my question is always how do we get it to scale and extremely affordable.

... and preferably pollute less than using wood in the first place.

Is wood considered a polutant when not burnt?

No, it is (largely, machinery aside) carbon neutral - provided we're growing said wood on existing forestry reserves or farmland, not wildland or old-growth forest.

Unless treated, it doesn't matter if wood is burned or left to decay as it will release the same amount of CO2 in the atmosphere anyway.

Well there's a time component to burning or leaving to decay. Leaving a tree to decay takes a long time and there's time for many other trees to grow in the meantime. Pretty safe.

In mature forests, the replacement time is pretty much 1:1. If you disregard the nutrients being taken away from the soil and the energy needed to transport and dry the wood, wood would be a pretty good fuel. Slightly worse than nuclear, I imagine.

Particulates from wood smoke are brutal.

(there are stoves that do better of course)

But then how much wood (and forestry) is needed to replace a good portion of the targeted market?

Is bone particularly tough though? I would have guessed some of the harder woods would already surpass or at least match it.

There was a standing joke during engineering undergrad that wood-along-the-grain always came out best on all the material selection charts. Essentially the answer to all questions about what material to use was "wood along the grain". I suspect that wood genuinely is close to being that good and its consistency (and the tricky across-the-grain bit) is what stops it being used everywhere.

Wood is also more of a fire risk than other materials.

This comes up when talking about the wooden skyscrapers being built. Maybe someone can elaborate, but, as far as I've heard, treated construction wood has pretty good fire-damage characteristics.

Wood is at the same time a combustible and fire-safe material. The required fire resistance of wood structures can be achieved by adding to the size of the structure, adding a protective cladding, using a non-combustible insulation material, or by improving the fire resistance of the wood structure with a fire-retardant treatment.

Steel and iron are also combustible even if that requires a high temperature. During bombing of Dresden in WWII that contributed to massive sustained fires.

Wood is very predictable under fire. In addition it is a good isolator so the high temperature does not spreed that fast. So it is quite straightforward to engineer things to be safe and give enough time for firemen to arrive.

Steel on the other hand not only looses its strength under high temperature, but it also conducts the heat very fast facilitating spread of fire. Accounting for that is non-trivial.

By "still" I assume you mean "steel"?

> it is quite straightforward to engineer [wooden] things to be safe and give enough time for firemen to arrive.

That time depends hugely on where you live.

Well, that's why local building codes exist.

Don't build a ten story wood building two hours from the nearest fire station.

Right, but I'm thinking more of whether you live in a developed country with decent public services. In huge swaths of the world building with pure wood is asking for a lot of trouble. (Happily (?) it's too expensive in most of those regions to be very popular.)

Add to that that "along-the-grain" also includes significant expansion and contraction due to humidity changes.

I am in an old house where years of expand-contract cycles on the wood framing have managed to wiggle out nails in places to the point where they stick 1/4in above the drywall surface.

Every house here in New Zealand is wood, and humidity is pretty high. I have never seen this except for decking, where nails are a bad option.

I’ve see nails move a lot after earthquakes (sort of tearing the framing and cladding).

Maybe we don’t see this as the weather is nearly always humid as we don’t get a real winter (so we don’t have a humidity cycle)?

Right, it's all about the cycle. Our climate goes from intensely humid in the summer, to bone dry in the winter - both because cold air in the negative double-digit Celsius temps is physically dry, and because our heat is forced-air. Then there are periods of high A/C use which also dehumidifies the air.

I believe wood expansion is primarily across the grain. More than an order of magnitude difference between radial and longitudinal

https://woodworking.stackexchange.com/questions/5871/which-d...

It varies significantly based on wood species.

Considering there has yet to be a dental crown that's as strong as a natural tooth, I'd imagine it's pretty far up there on the toughness chart.

Teeth aren't bones though.

In particular, the fracture properties of tooth are very different from those of bone. If I had to make a house out of one of them, I'd choose bone.

Bit of a side bar but the physical properties of parts of the human body are just amazing.

For example, the coefficient of friction for cartilage is 1/10 to 1/100 that of ICE [0]

0 - https://teambone.com/education/education-clinical/orthopedic...

What is the difference between "tough" and "hard"? I would use these terms interchangeably.

Hard : doesn't deform easily

Tough: doesn't break easily

So a pane of glass is hard but not tough. Lump of clay is tough but not hard.

There's quite a maze of twisty definitions of these, all slightly different, both in applied and theoretical flavours:

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

(warning: clickholes)

Toughness is how much energy something can take without breaking, e.g. the more weight you can put on a tabletop before it breaks in half, the tougher it is. The opposite of tough is brittle, if that makes more sense. Hardness is how much energy something can take without deforming, e.g. playdoh is not hard.

This and similar breakthroughs are truly thrilling to read about. They’re demonstrations that human ingenuity is being applied to combat climate change - and there are few forces on earth more formidable than human ingenuity. The fight is on, and we can win.

(True, human ingenuity got us into this mess in the first place.)

All that being said, it’s often worth reading these kinds of articles from the bottom up so as to avoid disappointment. I scrolled to the end first and found this:

“While shrinkage isn’t much of a problem when printing small objects, anything bigger could buckle or crack as the composite dries.”

They may solve this too, but it’s not time to celebrate just yet.

I guessed this might be buckthorn, but no

cellulose nanocrystals (CNC)

from the article:

"At the nanoscale, CNCs are stronger and stiffer than Kevlar. If the crystals could be worked into materials in significant fractions, CNCs could be a route to stronger, more sustainable, naturally derived plastics."

the original paper:

Printable, castable, nanocrystalline cellulose-epoxy composites exhibiting hierarchical nacre-like toughening

<https://link.springer.com/article/10.1007/s10570-021-04384-7> (paywall)

So it's FDM printable? Side note: I can see the overloading of "CNC" being confusing ;)

Two concerns, if anyone can answer:

1. Does it look like the production process can scale big enough?

2. Would that mean even more incentive to chop down trees?

The answer to question 1 for these sorts of articles is nearly always "no".

> 2. Would that mean even more incentive to chop down trees?

That might actually be a good thing - trees absorb carbon, which we need to do, quickly. We just need to make sure to plant new ones in their place.

Is that a sustainable practice you think? Just asking

Offhand, I don't see any reason why it couldn't be. What makes you think it might not be possible to do this sustainably?

The rate at which new trees grow. The ratio of carbon absorbed by a mature tree over the carbon another new tree (or trees) can absorb occupyig the same space on the ground

Earth has so much land that you could plant trees in though?

It really doesn't, most suitable land is used for farming already (sahara and siberian are not suitable)

Thats why specieces are dissapearing, because they have nowhere to live

It is literally impossible to plant enough trees to stop climate change.

You're misunderstanding what I wrote. What I claimed was:

(a) There is (at present) sufficient land for us to be able to sustainably plant enough trees to supply our need for such composites (including to the extent that they may substitute for our consumption of plastics), and

(b) Planting trees as part of this practice would likely be (non-trivially) beneficial in the fight climate change.

I did not claim that:

(c) Planting trees would somehow be sufficient to single-handedly solve climate change without us having to change any other of our current practices (like farming), or

(d) The planet would always have room for sufficient trees (for any purpose) regardless of how long current trends continue or how badly we continue to destroy more and more of the environment.

@dataflow but then you are dipping into the issue of artificially modyfing biomes. Putting forests where they didn't exist before, again, i don't know, but i would assume this could alter the local ecosystem and it should be done with care. Not just make the whole planet a forest. That's why i was concerned with using the same space.

I don't think you need to make the whole planet a forest for this to be feasible. Yes we use a lot of carbon, but not THAT much carbon. It would mess with some ecosystems (obviously), which is not ideal, but it wouldn't be that drastic of an alteration to the planet as a whole.

Also, the claim wasn't that this is perfect. Just that it's be (much) better than what we're doing currently.

What's wrong with making planet a forest? Right now we're shaping a planet into a concrete plain. I'd prefer forest any day.

I just said it should be done with care

A lot of the planet used to be forested that currently isn't. Many ecosystems have already been changed by removing forests, among other things. We can plant a lot of trees before we reach the point that we need to plant forests where none have been before.

And some ecosystems definitely could be improved by planting forests. They can halt desertification, for example.

We have to keep the carbon sequestered in the harvested wood. I suggest fleets of oceangoing megarafts, in preparation for the Waterworld apocalypse.

We have been sustainably farming trees for over 100 years.

Tree farming is probably one of the biggest issues in the pacific northwest today. They spray Glyphosate (round up) after every forest fire to prevent Aspen from growing (a natural firebreak), and then they plant GMO pine monocultures. This + pine beetle + putting out any small forest fires, lead to massive fuel build ups, which leads to massive forest fires (and subsequent flooding in the winter). It's definitely not sustainable.

Note that "is possible to do sustainably" and "is possible to do unsustainably" are not mutually exclusive.

Note that the claim actually being addressed was that we've been doing it sustainably, not merely that we could of we wanted to.

We have been doing it sustainably for hundreds of years. We've also been doing it unsustainably for a while, too. Different things happen in different places.

hmmm, lifespan of a tree is several hundred years.

How long does it take to know if the farm is sustainable?

Lifespan of some trees is several hundred years. You can go through pine generations much, much quicker (and people have, for hundreds of years).

So they've invented... MDF?

Interestingly the article switches back and forth between “hard as bone, tough as aluminum” and “hard as aluminum tough as bone”

Neither aluminum nor bone are very hard on the mohs or Rockwell scales though, so I assume toughness is the main desirable attribute.

From some quick Googling (no, I don't know the hardness of bone off the top of my head though having worked with it I can say it's quite soft just like aluminum), it looks like aluminum and bone aren't that different in hardness or toughness, with aluminum alloy being somewhat harder and tougher at the expense of higher density.

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