PLA, composting, recycling, and landfills
Jan. 31st, 2022 12:31 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
solarbirdSo I've been thinking a bunch about PLA - the plastic most commonly used in 3D printers, particularly at my hobby scale - and how to compost it and recycle/reuse it, and I'm still thinking of doing the latter in particular.
It's kind of a real topic in the 3D printing fora but I've been thinking about it and... I'm kind of thinking... maybe landfill is the good option.
Because here's the thing, and tell me if I'm missing something important, and I might be.
PLA breaks down safely. In a 50-60C commercial composting environment, it breaks down more than harmlessly, you can use it as brown matter in compost. In a body, it breaks down much more quickly and is again harmless - it's used medically.
People like the idea of composting PLA because - modulo additives like colourants - it breaks down so cleanly. You don't get the microplastics problem from it. That's pretty important.
But in a landfill, PLA doesn't really break down any faster than a petrol plastic. We're talking hundreds to over a thousand years, depending upon conditions.
And everybody's "well that's no better" but...
...what if that's good in this case? Since it doesn't break down in the terrible microplastics way. It still composts, it just takes ages.
Composting breaks it down to a few things, one of which is carbon dioxide.
That's bad.
But PLA is made entirely from plant matter. Corncobs are a big input stock. And it's over 50% carbon by weight. (36/71sts, 50.7%, molecular weight, roughly speaking.)
And the thing is... it's plant material. Plants get their carbon from the atmosphere, not the soil. That carbon came from the air, extracted by plants, thus removing carbon dioxide from the atmosphere.
If it breaks down, it's carbon neutral.
If it doesn't... and you put it in a landfill...
...isn't that carbon sequestration?
And that would be good.
I mean sure, it's medium-term only, but it's medium-term at a scale that gives us meaningfully more time.
I get these two 1kg rolls of PLA into a landfill and I've sequestered 1kg of actual carbon. And since what this is preventing is carbon dioxide, which has two oxygen molecules attached to that, I've prevented 3.67kg of carbon dioxide from forming.
(Modulo all the various costs in producing everything, of course, this is just about the material itself.)
Am I missing something? Because what I'm starting to think is... putting PLA in landfills sounds kinda great.
It's kind of a real topic in the 3D printing fora but I've been thinking about it and... I'm kind of thinking... maybe landfill is the good option.
Because here's the thing, and tell me if I'm missing something important, and I might be.
PLA breaks down safely. In a 50-60C commercial composting environment, it breaks down more than harmlessly, you can use it as brown matter in compost. In a body, it breaks down much more quickly and is again harmless - it's used medically.
People like the idea of composting PLA because - modulo additives like colourants - it breaks down so cleanly. You don't get the microplastics problem from it. That's pretty important.
But in a landfill, PLA doesn't really break down any faster than a petrol plastic. We're talking hundreds to over a thousand years, depending upon conditions.
And everybody's "well that's no better" but...
...what if that's good in this case? Since it doesn't break down in the terrible microplastics way. It still composts, it just takes ages.
Composting breaks it down to a few things, one of which is carbon dioxide.
That's bad.
But PLA is made entirely from plant matter. Corncobs are a big input stock. And it's over 50% carbon by weight. (36/71sts, 50.7%, molecular weight, roughly speaking.)
And the thing is... it's plant material. Plants get their carbon from the atmosphere, not the soil. That carbon came from the air, extracted by plants, thus removing carbon dioxide from the atmosphere.
If it breaks down, it's carbon neutral.
If it doesn't... and you put it in a landfill...
...isn't that carbon sequestration?
And that would be good.
I mean sure, it's medium-term only, but it's medium-term at a scale that gives us meaningfully more time.
I get these two 1kg rolls of PLA into a landfill and I've sequestered 1kg of actual carbon. And since what this is preventing is carbon dioxide, which has two oxygen molecules attached to that, I've prevented 3.67kg of carbon dioxide from forming.
(Modulo all the various costs in producing everything, of course, this is just about the material itself.)
Am I missing something? Because what I'm starting to think is... putting PLA in landfills sounds kinda great.
no subject
Date: 2022-01-31 10:34 pm (UTC)no subject
Date: 2022-01-31 11:14 pm (UTC)But... as a potential externalised side-benefit rather than externalised side-cost?
Goddamn I hope I'm right.
no subject
Date: 2022-02-01 12:10 am (UTC)A possible solution is for us to put all our landfills in desert locations, where it would be too dry to biodegrade.
no subject
Date: 2022-02-01 12:35 am (UTC)There are a few ways to do that - you can find plenty of studies showing how much more quickly PLA breaks down if you do it - and they measure the effectiveness of of these methods by rate of methane production.
What I'm suggesting is that accellerating breakdown to produce more methane is a bad idea. That putting PLA in an ordinary landfill of collected garbage, which doesn't get that treatment, leads to a breakdown path which is both more conventional and much, much longer, and more water/CO2 than methane.
(The PLA hydration reaction gives you formic acid and OH- which ends up back to carbon dioxide and water. So water doesn't seem to be a problem.)
no subject
Date: 2022-02-01 12:57 am (UTC)https://en.wikipedia.org/wiki/Formic_acid#Natural_occurrence
no subject
Date: 2022-02-01 01:19 am (UTC)I'm not suggesting we make more PLA intentionally as a long-term carbon sink, I'm just suggesting that of the options actually available, this one has the upside of providing medium-term carbon storage as an externalised benefit, which, of the options available, makes it the best and possibly even a net positive.
(I am not in any way suggesting this by itself is some kind of carbon solution. But I am saying maybe it can actively help a bit - be a net positive - thus making it the best and really only good answer for disposal of current waste PLA. Obviously, reuse is better, which is why I intend to produce PLA plastic sheet pieces, possibly for other makers as well as for myself. But eventually, you're going to be dealing with waste.)
no subject
Date: 2022-02-01 02:40 am (UTC)so it is an ant-acid
no subject
Date: 2022-02-01 02:45 am (UTC)( xD )
no subject
Date: 2022-02-01 02:49 am (UTC)no subject
Date: 2022-02-01 12:18 am (UTC)Shred waste, and use an auger to dump it into a big, sealed oven. CH4, CO2, and CO (along with nitrogen compounds) gets boiled off. Condense that, separate out the ammonia for fertilizer, and the CH4 and CO for power generation.
Drain off the heavy oils from the bottom of the oven. Distill, or dump in an old mineshaft to sequester carbon that way.
Put the leftover carbon-rich char into a shaker. Silicates and metal drop to the bottom, carbon sifts to the top. Dump the carbon in a deep, anoxic ocean trench, or use as a coal replacement.
no subject
Date: 2022-02-01 01:20 am (UTC)no subject
Date: 2022-02-01 03:29 am (UTC)no subject
Date: 2022-02-03 01:11 am (UTC)no subject
Date: 2022-02-07 03:14 am (UTC)You might be interested in this video where CNC Kitchen tries to compost PLA. He ultimately failed with his current setup, though it might be possible with the right composter and filament.