"Unlike conventional plastics, the monomers of PDK plastic could be recovered and freed from any compounded additives simply by dunking the material in a highly acidic solution. The acid helps to break the bonds between the monomers and separate them from the chemical additives that give plastic its look and feel."
Anyone know if any acid will work or if the solution is somehow special? Sounds like a big downside to lose acid resistance.
Looks like they use sulfuric acid at 0.5 to 5 M over a 24-hour period to depolymerize the plastics. So highly acidic, but probably better to keep your acids in polyethylene containers!
This is probably a dumb question, but what essential products use plastics and for which no other material is an adequate substitute for the plastic components?
That only changes the question to "are these products worth it?". I would argue there is a huge portion of consumer products that only use plastic because it is cheaper and the negatives of plastics were not in the equation at all.
It vastly depends on the product, but it is a question worth asking over and over again when we design products.
It has historically been plastic because it is cheap and readily altered to match the exact needs of the product. Rigid, soft, rugged, smooth, coarse, we can make a plastic suit.
Plastic cups are a good example, we have numerous materials at our disposal but we make disposable cups and containers out of plastic. Even bio-degradable plastic cups are a bad choice of material, as they take special circumstances to break down that many municipalities don't provide for and most users aren't carrying their bio degradable cups home to put in their compost. If they end up in the ocean, they will last just as long as other plastics. So that is bad product design, it doesn't take the full product lifecycle into account and ignores even it's typical usage of just a single serve drink used once.
Plastics have spoiled us too, so in many cases there probably isn't an alternative that is just as good. We may just have to accept that and find ways to make better materials out of more sustainable sources.
I would personally pick paper for single use cups. It is not perfect, still quite resource intensive to make and still unlikely to be recycled properly. But they can at least be sustained through sustainable forestry and the waste will degrade in the most likely places it will end up.
Remember, that plastic is not just cheaper -- it's also often lighter. We could do a lot of stuff with metal, wood or good old granite, but emissions from manufacturing transporting all those heavier goods would spike and we don't want that as long as manufacturing and transporting are dependent on fossil fuels.
Plastic is fine. It has it's uses, and we won't get rid of it anytime soon. We need to get rid of the bulk of the one-time use stuff though, and focus on re-usable items if we want to change something.
I agree, your last paragraph is how I feel about the situation summed up. It is an excellent material, but we waste it on single use expendable items that we could really do without.
I do want to add though that if we had greener transport, then heavier items wouldn't be that big of a deal. So if we are playing the long game, that would almost be a good incentive for transport and industry to be more efficient in the long run.
The medical field comes immediately to mind, from implants through to flexible tubing. I mean, I suppose you could make the tubing for a peristaltic pump from cat gut or something.
Lots of medical and lab supplies, such as tubing, tools, and stents. For some applications glass is too fragile, metal can be too reactive. Even "inert" metals like titanium or nickel eventually develop bio-films.
Various plastics' combination of temperature stability at both high and low temps (cryo / autoclave), non-bio-reactivity (body doesn't attack or reject over short spans), and corrosion resistance makes plastics perfect for these situations. Especially wet situations. And since plastics can be fine tuned for application specific needs they can be iterated on quickly with a materials but not manufacturing process change in some cases.
My wife and I had this conversation a couple weeks ago asking this very question which ultimately boils down to: "Are plastics worth it at all ever?" And the answer we found, surprisingly, was yes.
Aren't plastics usually reasonable to burn as well? As in burning mostly produces CO2 and water? Or do common plastics contain some nasty atoms we dont want in the air in any way?
Plastics often are doped with heavy metals like molybdenum to affect mechanical properties like wear resistance, or bromine for fire resistance. Neither of which you want in your lungs.
They can be burned safely in an incinerator. Ad hoc burning can produce very toxic chemicals, though, including dioxins, hydrogen cyanide, vinyl chloride and furans. It could release lead. It depends on the type of plastic (PVC? Polyethylene? Polypropylene?). This is why it’s troubling to see people burning bags of trash and tossing in plastic bags and soda bottles as if they magically disappear.
“When plastic is burned, it releases dangerous chemicals such as hydrochloric acid, sulfur dioxide, dioxins, furans and heavy metals, as well as particulate.”
Sure, plastics are wonderful materials. The problem is that they are too good for their price. And that's the folly: plastics are simply too cheap.
Because of that, we treat plastic things as disposable, which is how most of plastic waste is produced.
There is a very simple way to address plastic pollution: make plastic expensive again. Even a minor measure like a 10-cent tax on a bag is disproportionately effective.
To put it in context, if you forgot how much we are willing to pay for a bag, stop by a bag store.
An expensive application of plastic (medical, etc) won't be affected much, if at all, by a plastic tax.
So I still don't know why we're not doing it big time. Oh wait, I do know, it's greed[1]. As usual, the profits from such misuse if plastics will be privatized, and the losses socialized (we'll all pay for cleanups with tax money and/or suffer from pollution).
Exactly! Thanks for the link. We were discussing this in the context of the reduction of oil consumption world-wide eventually leading to higher cost of plastics overall and which areas could it have a large effect.
This is actually a known economic problem that has been repeated with grazing commons in england and fishing reefs, plastics have a significant cost externality[1] that isn't being identified in current pricings and needs to be added by governments (or whatever) to account for their "real cost".
I think for some of those things like medical tubing, if we didn't have plastics we would be using things like leather or tripe or sinew or other natural solutions (I'm not an expert here). Not to say plastic isn't better, but it's not the only way of doing it.
As some siblings have pointed out there are specific uses plastics are good for - and I don't think the goal should be to reduce plastic usage to zero. I think it's more important to go after stupid consumer product usages of plastic that are unnecessary, a moderate amount of plastic use and reuse is totally reasonable and sustainable, when we have half the mass being tossed away in the form of clamshells then we have an issue.
I agree. Yesterday the IT department brought me a big box of USB hard drives. I spent an hour unpacking them and after setting the recyclable cardboard aside was left with a mountain of plastic shells that were used for shock absorption and peg hangars.
IMO, there's no reason these couldn't have been made of cardboard as well.
There are few things that couldn't possibly be done without plastic, but most of things do benefit from being plastic to various degree. People mention various material properties crucial to medical use, but I'd mention a simple other one: mass. If you tried to replace plastics with metals and glass in consumer products while retaining similar material properties, you'd end up with a lot heavier products. Think e.g. plastic bottle vs. glass bottle for an obvious example. All that mass increases fuel used whenever you have to move it.
This alone doesn't justify use of plastics everywhere, but it does matter at scale and over lifecycles of some products, so it's worth remembering.
Aluminium has similar weight to volume ratio for small applications, and is the easiest to recycle, but is not aesthetically pleasing. Hopefully something like ALON (transparent aluminium ceramic) could come to the consumer market at some point?
True, and the original lining ended up being banned as an endocrine disruptor (BPA). I’d guess the lining is more for protecting the integrity of the metal than food safety.
A middle-ground alternative would be returning to glass once transportation is fully electric and based on clean energy. Still lots of downsides, not an easy problem to solve.
For some products, I wonder if using glass would result in less transport costs over the long term.
I think specifically of milk bottles.
Plastic milk bottles have to be brought from hundreds of miles away to my local dairy. Post-consumer, they're trucked close to 50 miles to the nearest landfill, or a couple of hundred miles to the nearest reprocessing company, or thousands of miles to another country's reprocessing facilities.
By contrast, glass milk bottles (widely available in the last five cities in which I've lived) are trucked to the dairy once. Then post-consumer they get returned to the same dairy for cleaning and re-use over and over and over again. Some bottles have clearly been through this process many times, as they show signs of wear and have less clarity than the random new glass bottle.
I prefer re-using things to recycling things, but I'm apparently in the minority. When I mentioned glass milk bottles at work once, nobody knew what I was talking about, even though I know they've seen them since we all shop at the same supermarkets.
I'm in the "reuse over recycle" camp myself, and heard plenty of stories about milk bottles from my parents and grandparents, so I understand this point.
Instinctively, I'd wish we got back to reusable glass bottles for most things; as inconvenient as they are when shopping, maybe we could get that back in the era of increasing home delivery of groceries. That said, I recall someone on HN bringing up the following point: plastics are probably energetically cheaper to manufacture than their reusable equivalents. For plastic bags, I think the ratio was around 1000 uses before a reusable "eco" bag started to come ahead of disposable plastic bags, energy-wise. I suspect the calculation for glass bottles will be similar, once you account for the costs of cleaning.
Ecologically speaking, AFAIK the main problem with disposable plastics isn't their carbon footprint, but microplastics getting into the food chain. That means better garbage management is the crucial issue here.
I'm not saying this to defend the proliferation of disposable plastics - in fact, I have an instinctive and deep hate for single-use items where reusable alternatives could exist. I'm only saying this problem is nontrivial once you start accounting for energy use, or negative externalities. If there's some detailed analysis that tackles this issue thoroughly, I'd love to read one and update my views.
A very good question, actually, and one which gets to the heart of materials science. Which is nowhere near my areas of expertise, though I've been looking into this incidental to other interests.
Meta-answering by way of what the pre-plastic world looked like....
The history of the study itself is interesting: materials science & engineering grew mostly out of mining engineering, which subsumed metallurgy (see Agricola's De Re Metalica, still a leading text through the early 20th century, or the evolution of M.I.T.'s course catalogue), but picked up other elements (so to speak) especially with the rise of coal-tar and petroleum (organic) chemistry. There was the golden age of plastics, roughly 1920-1940, when many modern polymers were invented (polystyrene, polyester, PVC, Nylon, etc.). Earlier, ~1840s-1890s rayon and celluloid (from plant fibres) and bakelite (coal tar).
You can look at what materials were used before plastics were available. Early 20th century children's toys were often made of stamped tin. Wood, woven fibres or reeds (baskets, wicker or rattan furniture), fabrics, hides, metals, and stone, were commonly used. Plastics replaced many of these on the basis of cost, weight, flexibility, mouldability, process-scalability, automation, and frequently durability, as well as water-, air-, and rot-resistance.
Human use of materials gives a strong sense of time. In film and theatre, much of the atmosphere of an era, beyond mere styling, derives from the materials used or incorporated: stone, brick, plaster, ceramics, wood, fibres, dyes, glass, metals, and synthetics. Mid-century US clothing is dominated by wool and leather, the 1960s mood is set by synthetcs and plastics, 1970s by polyester. Since then there's been a movement back to more natural fabrics generally, though nylon outerwear cold-weather garments are still popular.
Many of the shifts in material use are energy-bounded. Not merely in processing (metals smelting, glass and ceramics production), but in transport and sourcing. Paris's catacombs, I've just learned, were largely formed as quarries for building materials. Almost all pre-modern construction used locally-sourced materials, or materials which could be moved nearly entirely by water, with minimal thermal processing.
Lumber use was historically minimised due to its scarcity -- half-timbered and full-brick or stone construction limit wood use for a few weight-bearing members, and fill planes and voids with more-abundant materials -- stone, wattle-and-daub, lathe-and-plaster, brick, even straw. (Fire risk was another consideration restricting wood construction in pre-modern cities.) Whilst the US had vast forests at its founding, they were largely consumed within about a century, for both construction and fuel. Despite its coal riches, wood use exceeded coal through the 1880s. (Oil surpassed coal only in the 1950s.)
With coal, steam, rail, excavators, drilling rigs, pipelines, and tankers, sourcing vast amounts of coal and oil from inconvenient remote locations and synthesizing useful fabrication and construction materials became possibe. Voila: Plastic age. Metal mining, refining, smelting, and founding also advanced rapidly -- highly-reliable, high-power locomotives, rails, pipelines, and steamships were infeasible prior to Bessemer steel (1860s). Aircraft required aluminium structural members and fuselage panels (1880s). So there's a complex bootstrap process involved.
(This isn't a defence of plastics, just a brief, very rough, and non-expert materials/economic history.)
Semi-OT, one of my favourite pre-plastics engineering solutions. How do you hold 5 million cubic feet of hydrogen gas in an era before synthetic polymers?
Oxgut. Hand-glued.
"Engineer Guy" Bill Hammack's knowledge is captivating and his enthusiasm infectious:
anyone that has a breathing issue uses plastic in all the hose connections up to the oxygen machine...my Father uses such a machine and those tubes regularly fail after awhile and need replacing..I usually get the job of replacing them..
Look as though the polydiketoenamines themselves are also quite easy to make;
>"Surprisingly, polydiketoenamines could be made simply by mixing ketones and amines. ‘It’s a click reaction that works at room temperature, without needing catalysts, additives or even a solvent,’ says Helms. ‘They just require a few minutes in a ball mill.’"
Hmmm, last I checked concentrated sulfuric acid is not commonly available to or advised to be used by the public . . . so forget about the common man recycling this stuff, just another development of "big corporate" to keep this product and the system surrounding it all within their clutches. On the other hand, my son and I just filed a patent for a low melt temp polymer system that is flexible, recyclable merely with low heat, biodegradeable (without acids), repurposeable, NON TOXIC, and all processes can be done at home safely by the public, no corporate involvement necessary.
> Hmmm, last I checked concentrated sulfuric acid is not commonly available to or advised to be used by the public
IIRC, lead-acid batteries, common in automobiles, contain a somewhat concentrated form of sulfuric acid; they are also made of plastic, so assuming they continue to be available, I doubt that such batteries will use this new plastic.
I'm kinda curious if this "new" plastic is going to be flexible enough in the number of applications to replace most common plastics in common applications, or if it's going to have the same issues (ie, needing fillers or other things to make it work for certain applications).
What is it's heat resistance? How well does it work in extreme cold? How flexible is it? Impact resistance? Can it be made clear?
Maybe any fillers, etc can also easily separate out?
If it can replace most uses of PP/PE/ABS/PVC - it would be huge on the consumer market (also, providing it doesn't have a similar BPA-like issue).
49 comments
[ 2.1 ms ] story [ 87.9 ms ] threadAnyone know if any acid will work or if the solution is somehow special? Sounds like a big downside to lose acid resistance.
It has historically been plastic because it is cheap and readily altered to match the exact needs of the product. Rigid, soft, rugged, smooth, coarse, we can make a plastic suit.
Plastic cups are a good example, we have numerous materials at our disposal but we make disposable cups and containers out of plastic. Even bio-degradable plastic cups are a bad choice of material, as they take special circumstances to break down that many municipalities don't provide for and most users aren't carrying their bio degradable cups home to put in their compost. If they end up in the ocean, they will last just as long as other plastics. So that is bad product design, it doesn't take the full product lifecycle into account and ignores even it's typical usage of just a single serve drink used once.
Plastics have spoiled us too, so in many cases there probably isn't an alternative that is just as good. We may just have to accept that and find ways to make better materials out of more sustainable sources.
But, I missed it if you said it - what material should we ideally use for disposable cups, currently?
Plastic is fine. It has it's uses, and we won't get rid of it anytime soon. We need to get rid of the bulk of the one-time use stuff though, and focus on re-usable items if we want to change something.
I do want to add though that if we had greener transport, then heavier items wouldn't be that big of a deal. So if we are playing the long game, that would almost be a good incentive for transport and industry to be more efficient in the long run.
Various plastics' combination of temperature stability at both high and low temps (cryo / autoclave), non-bio-reactivity (body doesn't attack or reject over short spans), and corrosion resistance makes plastics perfect for these situations. Especially wet situations. And since plastics can be fine tuned for application specific needs they can be iterated on quickly with a materials but not manufacturing process change in some cases.
My wife and I had this conversation a couple weeks ago asking this very question which ultimately boils down to: "Are plastics worth it at all ever?" And the answer we found, surprisingly, was yes.
edit: a typo.
Done improperly, you end up with a very snokey, sooty smoke.
Done properly, you’re dealing with very high T, which is hard, and NOx production.
But, assuming you’re doing a good job... burn baby burn!
(Just separate out the per-fluorinates - HF is nasty)
This is a good rundown: https://www.directplastics.co.uk/about_plastics/post/whats-i...
MIT says... https://engineering.mit.edu/engage/ask-an-engineer/can-we-sa...
“When plastic is burned, it releases dangerous chemicals such as hydrochloric acid, sulfur dioxide, dioxins, furans and heavy metals, as well as particulate.”
Because of that, we treat plastic things as disposable, which is how most of plastic waste is produced.
There is a very simple way to address plastic pollution: make plastic expensive again. Even a minor measure like a 10-cent tax on a bag is disproportionately effective.
To put it in context, if you forgot how much we are willing to pay for a bag, stop by a bag store.
An expensive application of plastic (medical, etc) won't be affected much, if at all, by a plastic tax.
So I still don't know why we're not doing it big time. Oh wait, I do know, it's greed[1]. As usual, the profits from such misuse if plastics will be privatized, and the losses socialized (we'll all pay for cleanups with tax money and/or suffer from pollution).
[1]https://www.bizjournals.com/memphis/news/2019/01/08/plastic-...
[1] https://en.wikipedia.org/wiki/Externality
IMO, there's no reason these couldn't have been made of cardboard as well.
But, if you want a real environmental shit-show read up of per fluorinate manufacturing.
Teflon, gore Tex, etc is the real deamon children of the polymer industry.
The great thing about plastics is their high durability and low cost of production.
The main problem with plastics is their high durability and low cost of production.
This alone doesn't justify use of plastics everywhere, but it does matter at scale and over lifecycles of some products, so it's worth remembering.
I’ve heard that aluminium pots and pans, as well as traces in things like salt, are strongly linked to Alzheimer’s.
A middle-ground alternative would be returning to glass once transportation is fully electric and based on clean energy. Still lots of downsides, not an easy problem to solve.
I think specifically of milk bottles.
Plastic milk bottles have to be brought from hundreds of miles away to my local dairy. Post-consumer, they're trucked close to 50 miles to the nearest landfill, or a couple of hundred miles to the nearest reprocessing company, or thousands of miles to another country's reprocessing facilities.
By contrast, glass milk bottles (widely available in the last five cities in which I've lived) are trucked to the dairy once. Then post-consumer they get returned to the same dairy for cleaning and re-use over and over and over again. Some bottles have clearly been through this process many times, as they show signs of wear and have less clarity than the random new glass bottle.
I prefer re-using things to recycling things, but I'm apparently in the minority. When I mentioned glass milk bottles at work once, nobody knew what I was talking about, even though I know they've seen them since we all shop at the same supermarkets.
Instinctively, I'd wish we got back to reusable glass bottles for most things; as inconvenient as they are when shopping, maybe we could get that back in the era of increasing home delivery of groceries. That said, I recall someone on HN bringing up the following point: plastics are probably energetically cheaper to manufacture than their reusable equivalents. For plastic bags, I think the ratio was around 1000 uses before a reusable "eco" bag started to come ahead of disposable plastic bags, energy-wise. I suspect the calculation for glass bottles will be similar, once you account for the costs of cleaning.
Ecologically speaking, AFAIK the main problem with disposable plastics isn't their carbon footprint, but microplastics getting into the food chain. That means better garbage management is the crucial issue here.
I'm not saying this to defend the proliferation of disposable plastics - in fact, I have an instinctive and deep hate for single-use items where reusable alternatives could exist. I'm only saying this problem is nontrivial once you start accounting for energy use, or negative externalities. If there's some detailed analysis that tackles this issue thoroughly, I'd love to read one and update my views.
Meta-answering by way of what the pre-plastic world looked like....
The history of the study itself is interesting: materials science & engineering grew mostly out of mining engineering, which subsumed metallurgy (see Agricola's De Re Metalica, still a leading text through the early 20th century, or the evolution of M.I.T.'s course catalogue), but picked up other elements (so to speak) especially with the rise of coal-tar and petroleum (organic) chemistry. There was the golden age of plastics, roughly 1920-1940, when many modern polymers were invented (polystyrene, polyester, PVC, Nylon, etc.). Earlier, ~1840s-1890s rayon and celluloid (from plant fibres) and bakelite (coal tar).
Vaclav Smil has an excellent book on materials, Making the Modern World, which looks at sourcing and usage (https://www.worldcat.org/title/making-the-modern-world/oclc/...). Strongly recommended.
You can look at what materials were used before plastics were available. Early 20th century children's toys were often made of stamped tin. Wood, woven fibres or reeds (baskets, wicker or rattan furniture), fabrics, hides, metals, and stone, were commonly used. Plastics replaced many of these on the basis of cost, weight, flexibility, mouldability, process-scalability, automation, and frequently durability, as well as water-, air-, and rot-resistance.
Human use of materials gives a strong sense of time. In film and theatre, much of the atmosphere of an era, beyond mere styling, derives from the materials used or incorporated: stone, brick, plaster, ceramics, wood, fibres, dyes, glass, metals, and synthetics. Mid-century US clothing is dominated by wool and leather, the 1960s mood is set by synthetcs and plastics, 1970s by polyester. Since then there's been a movement back to more natural fabrics generally, though nylon outerwear cold-weather garments are still popular.
Many of the shifts in material use are energy-bounded. Not merely in processing (metals smelting, glass and ceramics production), but in transport and sourcing. Paris's catacombs, I've just learned, were largely formed as quarries for building materials. Almost all pre-modern construction used locally-sourced materials, or materials which could be moved nearly entirely by water, with minimal thermal processing.
Lumber use was historically minimised due to its scarcity -- half-timbered and full-brick or stone construction limit wood use for a few weight-bearing members, and fill planes and voids with more-abundant materials -- stone, wattle-and-daub, lathe-and-plaster, brick, even straw. (Fire risk was another consideration restricting wood construction in pre-modern cities.) Whilst the US had vast forests at its founding, they were largely consumed within about a century, for both construction and fuel. Despite its coal riches, wood use exceeded coal through the 1880s. (Oil surpassed coal only in the 1950s.)
With coal, steam, rail, excavators, drilling rigs, pipelines, and tankers, sourcing vast amounts of coal and oil from inconvenient remote locations and synthesizing useful fabrication and construction materials became possibe. Voila: Plastic age. Metal mining, refining, smelting, and founding also advanced rapidly -- highly-reliable, high-power locomotives, rails, pipelines, and steamships were infeasible prior to Bessemer steel (1860s). Aircraft required aluminium structural members and fuselage panels (1880s). So there's a complex bootstrap process involved.
(This isn't a defence of plastics, just a brief, very rough, and non-expert materials/economic history.)
Oxgut. Hand-glued.
"Engineer Guy" Bill Hammack's knowledge is captivating and his enthusiasm infectious:
https://www.youtube.com/watch?v=ixxXhZVFXxQ
https://www.popularmechanics.com/flight/airlines/a16637939/b...
>"Surprisingly, polydiketoenamines could be made simply by mixing ketones and amines. ‘It’s a click reaction that works at room temperature, without needing catalysts, additives or even a solvent,’ says Helms. ‘They just require a few minutes in a ball mill.’"
https://www.chemistryworld.com/news/new-family-of-polymers-c...
IIRC, lead-acid batteries, common in automobiles, contain a somewhat concentrated form of sulfuric acid; they are also made of plastic, so assuming they continue to be available, I doubt that such batteries will use this new plastic.
What is it's heat resistance? How well does it work in extreme cold? How flexible is it? Impact resistance? Can it be made clear?
Maybe any fillers, etc can also easily separate out?
If it can replace most uses of PP/PE/ABS/PVC - it would be huge on the consumer market (also, providing it doesn't have a similar BPA-like issue).