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Comment by montjoy | Hacker News Reader

> and can be easily manufactured in large quantities

That seems promising.

I have a couple of concerns - Can it be recycled? - How are new materials like this tested for toxicity?

I agree with concerns about recyclability. I would also raise concerns about the renewability and/or toxicity of the base materials. If they are petroleum-based, this feels like a losing proposition.

Unfortunately the recyclability and the lack of toxicity are contradictory, they cannot be satisfied simultaneously for this kind of materials.

As long as the 2-dimensional polymeric sheets do not decompose, they will not be toxic, as they cannot enter a living cell (in the form of fine dust they could cause the same problems as any mineral dust, e.g. respiratory damage through purely mechanical action).

However if they do not decompose, they can be recycled only by burning.

If they can be decomposed into monomers by heat, light or chemicals, then the monomer can be recycled. However in that case some spontaneous decomposition will also occur in old objects made of the 2-dimensional polymer and the released monomer molecules would cause toxicity problems.

So only one of these 2 features must be chosen and optimized.

Plastics can be toxic by leaching additives without the polymer itself breaking down. Moreover, much of the damage caused by microplastics (i.e. only mechanically broken down) is poorly understood. At the very least, they seem to harbour novel collections of microbes that aren't necessarily benign.

Poly(lactic acid) can be decomposed into lactate monomers by water, and the released lactate monomer can be oxidized to pyruvate and used as food by the Krebs cycle, or converted to glucose via gluconeogenesis. The lethal dose is in the grams per kilogram, so it won't cause toxicity problems.

The article mentions that it's melamine, which we currently find in Magic Erasers. It isn't recyclable or biodegradable, but seems to be non-toxic enough to be a regular fixture in the household cleaning arsenal.

It would be far better to use it as (long-lived) building material than as a sponge that quickly degrades and gets rinsed down the drain.

1. https://livegreen.recyclebank.com/column/because-you-asked/w...

Melamine is in widespread use for kitchen furniture surfaces. It is not recyclable, usually it's landfilled or burned.

It is quite certain that a 2-dimensional polymer cannot be recycled like metal, glass or a thermoplastic material, i.e. by remelting or by plastic deformation at high temperatures, because a 2-dimensional polymer cannot be deformed without breaking covalent bonds and it cannot flow in a liquid state.

So this new material might behave like the existing cured polymeric resins, e.g. epoxy resins, which form a 3-dimensional network of covalent bonds after curing, so they cannot be melted, and which when heated decompose before melting. Such materials can usually be recycled only by burning.

Nonetheless, there might be a more complex way to recycle the new materials, if the new materials would decompose in monomer molecules when heated or if there would exist some solvent able to break the bonds between monomer molecules, transforming the solid 2-dimensional polymer into a solution of the monomer molecules.

If such a method to depolymerize the 2-dimensional polymer would exist, the obtained monomer could be reused to synthesize again 2-dimensional polymers.

If the depolymerization is impossible then these materials would be used in the same way like the already existing and widely used insoluble and infusible polymeric resins.

More important for their success is what processing methods will be applicable for them. After the 2-dimensional sheets are formed, they cannot be processed by any of the popular methods, e.g. injection in a mold. The thermoset polymers behave similarly after curing, but they are produced in a state where they are only partially polymerized in 1-dimensional molecules, so they can be molded in the final shape and the complete polymerization happens later.

For now, it seems that these new 2-dimensional polymers can be made only as sheets, and then you must cut them in the shapes that you need, which will waste material in comparison with making the same shape from a thermoplastic or thermoset material.

Another problem not mentioned is that of the fracture toughness. They have made some tensile strength measurements and there is no doubt that the 2-dimensional polymers will have outstanding tensile strength. However the problem is which will be their fracture toughness for bending. Graphite has a similar structure and it also has excellent tensile strength in the direction parallel with the sheets, but it is also extremely fragile when you bend it.

An advantage of the 1-dimensional polymers is that they, like metals, can be deformed without breaking covalent bonds, which results in high fracture toughness for metals and 1-dimensional polymers, unlike the substances with 2-dimensional networks of covalent bonds (e.g. graphite) or 3-dimensional networks of covalent bonds (e.g. diamond), which are fragile.

So more research is needed to determine how useful these 2-dimensional polymers can really be.

In any case, just achieving their synthesis is already a very impressive result.

Your answer illustrates why, after all these years, HN is still one of the best places to lurk. As someone who forgot most of what he learned in HS chemistry, and didn’t take any collegiate courses, what material would you recommend to learn about this stuff?

I am sorry but I cannot give a good recommendation as some years have passed since I have last searched for chemistry books in this domain.

If you go to Amazon and you search, e.g., for "Polymer Chemistry" and for "Materials Chemistry", you will find much more than 100 books. However I do not know which are the best among the recent books.

A less risky way than ordering such a book, and finding after paying for it that it is a dud, would be to go to an online site like Library Genesis, search there for such books (there are plenty), browse through them and maybe, if you find what you need, choose one or more to buy in printed form.

Alternatively, you can read the Amazon reviews for such books, to determine which would be worthy. The Amazon reviews for such specialized items as a science book are usually more trustworthy than for items of general interest.

Thx for the Library Genesis pointer - looks like a fantastic resource!

Not the person you're replying to but William D Callister's Material Science and Engineering is a pretty standard engineering book I've seen used in my different universities across 2 continents (and have studied from too), so I'm going to say that it's a good starting point.

You seem to be assuming that the 2D polymers extend indefinitely. If instead their growth is limited such that the molecules tile, overlap, and layer, they may be more amenable to manipulation such as thermoforming, thermosetting, etc.

The paper claims that they have obtained 2D sheets of very large extent, not small flakes that can overlap.

The advantages that they claim over conventional polymers, e.g. inpermeability and high tensile strength, are conditioned by such large extents. If the 2D sheets would be small enough to slide over each other and insert between other sheet fragments, so that plastic deformation would be possible, then they would also lose any advantages over traditional polymers.

> If the 2D sheets would be small enough to slide over each other and insert between other sheet fragments, so that plastic deformation would be possible, then they would also lose any advantages over traditional polymers.

I suspect that as with many composites, these qualities fall along a spectrum, and that there are significant nonlinearities (as in "a little goes a long way") that can be usefully exploited.

> a couple of concerns - Can it be recycled?

Right. We have enough issues with plastic waste, without it having extra-ordinary strength.

Also steel is 100% recyclable. If I recall correctly, most steel used today is recycled.

Most steel in the US and Europe is recycled. I believe most steel in China and to a larger extent Asia comes out of a giant pit in Australia.

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

That mine runs fully automated ore trucks and the owner Rio Tinto wants to automate the rest. 950 ppl produce 18% of the world's iron ore from that pit.

https://www.abc.net.au/news/2015-10-18/rio-tinto-opens-world...

If this has 100x less carbon footprint and steel is 90% recycled, the polymer still wins overall.

Not in 10,000 years when it is still blowing around..

Current steel production is pretty awful too - radioactive materials in atmosphere via coal, leachates from additives, etc.

Microplastics haven't been proven to have much damage other than triggering karentils (karen's on lentil spectrum).

It's possible the strength could reduce microplastics?

Or increase the risk posed by microplastics.

Very tiny, very sharp flakes of very strong materials could be asbestos 2.0

I imagine that even things that are nominally strong might be susceptible to things like UV. But IANAC.

Isn't the tradition that something reaches mass market before whatever suppression and disinformation campaigns, paid for by the industry, before there's a strong enough response and therefore reaction by elected officials - who otherwise don't pay attention to such issues? Hopefully it's not harmful/toxic, but we don't seem to have an apparatus that counters the above influence; sugar, cigarettes, asbestos, etc.

Yes- this is exactly what I’m afraid of.

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