Ask Hackaday: Is PLA Biodegradable?

The most popular plastic for 3D printers is PLA – polylactic acid – a plastic that’s either derived from corn starch, inedible plant detritus, or sugar cane, depending where in the world it was manufactured. Being derived from natural materials, PLA is marketed as being biodegradable. You don’t need to worry about low-poly Pokemon and other plastic trinkets filling landfills when you’re printing with PLA, all these plastic baubles will return to the Earth from whence it came.

3D printers have been around for a few years now, and now objects printed in PLA have been around the sun a few times. A few of these objects have been completely forgotten. How’s that claim of being biodegradable holding up? The results are mixed, and as always, more data is needed.

A few weeks ago, [LazyGecko] found one of his first experiments in 3D printing. In 2012, he was experimenting with tie dying PLA prints by putting his prints in a jar filled with water and blue dye. This jar was then placed in the back of his cupboard and quickly forgotten. 3.5 years later, [LazyGecko] remembered his experiment. Absolutely nothing happened, save for a little bit of blue dye turning the print a pastel baby blue. The print looks and feels exactly like the day it came off the printer.

[LazyGecko]’s blog post was noticed by [Bill Waters], and he has one datum that points to PLA being biodegradable. In 2015, [Bill] printed a filter basket for his fish tank. The first filter basket worked well, but made a small design change a week later, printed out another, and put the first print in storage. He now has two nearly identical prints, one in constant use in a biologically interesting environment, the other sitting on a shelf for a year.

[Bill]’s inadvertent experiment is very close to the best possible experimental design to make the case for PLA biodegradability. The 3D printed filter basket in constant use for a year suffered significant breakdown, and the honeycomb walls are starting to crumble. The ‘inert’ printed filter basket looks like it just came off the build plate.

If that’s not confusing enough, [Bill] also has another print that has spent a year in a fish tank. This end cap for a filter spray bar didn’t see any degradation, despite being underwater in a biologically active environment. The environment is a little different from a filter basket, though; an aquarium filter is designed to break down organics.

To answer the question, ‘is PLA biodegradable,’ the most accurate answer is, ‘maybe’. Three data points in uncontrolled environments isn’t enough to draw any conclusions. There are, undoubtedly, more forgotten 3D prints out there, and more data to back up the claim of PLA being biodegradable.

This is where you come in. Do you have some forgotten prints out there? Your input is needed, the fruits of your labors are evidence, your prints might be decaying and we want to know about it below.

79 thoughts on “Ask Hackaday: Is PLA Biodegradable?

    1. No, not really. You need a controlled environment so you can have some idea what you are measuring, and you need to have proper controls. Next try to make you experiment double-blind, so that the examiner does not know the conditions of the part she is grading. And while we are at it, make sure that you have a big enough sample size so you can actually draw some conclusions from the data. And to draw proper conclusions, you need to know what exactly you are asking: ‘is PLA (bio)degradable’ is silly, that is a known fact. ‘Are 3D-printed PLA parts biodegradable’ is better, but that still leaves open the definition of ‘3D printed’ and ‘PLA’. Is all PLA filament the same?
      The scant data-points in the article make it just a collection of biased opinions, IMHO not worthy of the attentions the whole discussion has been getting online.

      1. The double blind part is completely unnecessary for an engineering study, I worked in a PLA lab and we would use TGA or environmental chambers to test degradation.

        A better DoE would be having identical parts printed of identical mass. Place them in aeration and biodegradation chambers to speed up your timeframe. Control for temperature, time spent, and maybe environment pH if you are feeling frisky.

        The question should be “Under what conditions or times does PLA degrade best in?”. I agree though, this has been studied to death and we know PLA is bio degradable. The issue is manufactures often beef up the PLA with fillers or additives to save cost or improve properties. So, you get to claim that you are using “Biodegradable PLA” but you’re also using 35 percent talc or starch.

        1. Also, putting PLA in a sealed jar of water in the dark isn’t exactly testing its BIOdegradability. That’s testing its waer solubility. Shocking that in a reef tank, where there’s a crapload of microorganisms (and also probably a lot of UV light) the stuff degrades.

          1. I can confirm this. I printed a thin mesh designed to seed algae for an algae turf scrubber. It was rubber banded to the output of my skimmer overflow (it’s a hang on back design). I have had to reprint the mesh several times because it breaks down in about 6 months, completely failing and crumbling. I knew this would happen. On the other hand I printed a soap tray for a washing machine made by LG. This was a state of the art machine with a flaw so I decided to fix it. I used the same PLA to print the tray. It gets hit with water and detergent at least twice a week. It still looks like the day I printed it.

            TL;DR: PLA is biodegradable, not dissolvable by water alone.

          1. There’s still something to be learned from burying a PLA print in a compost pile. It’s easy to do. And it would prove PLA *can* biodegrade. Amateur scientists have their place, often making discoveries that more advanced labs then elaborate on and make more specific. Perhaps have some temperature probes and log the temperature over time, put one new print in each month to see how much degradation takes place over time. There’s lots of useful things to learn. Especially if the current state of the art is a guy with a fish tank.

        1. Especially as there is no necessity for double blindness in this case. The amount of degradation can be measured objectively by several means. The easiest would be weight – the mass-loss by degradation. Surface roughness or color change are other criteria. Parts of suitable geometry can also be tested for tensile strength.

          1. Agreed. Double-blind studies are only effective when studying people, experiments like this are hindered by double-blind studies, and in any case a “double-blind” is really only a “single-blind” because the plastic cannot tell it’s in an experiment. Don’t blind the researchers!

      2. Double, our even single, blinding an experiment with no human test subjects is a waste of time and completely unnecessary.

        Your attitudes and expectations aren’t going to affect microbes or chemical processes.

        1. Not entirely true. Double blind doesn’t make any sense in context – the PLA doesn’t know what conditions it’s in, so you don’t exactly need to hide which branch of the study it’s in. But single blinding can be useful. For example, the ‘degree of decomposition’ is probably going to be fairly subjective, so it’s better if the person evaluating it doesn’t know the material it’s made of or what conditions it was stored in. Keeps accidental bias from creeping in.

          1. To be any use, “degree of decomposition” is going to have to be stuff you can put numbers on. Remaining intact mass, chemical composition, stuff like that. Maybe even material strength, and particularly how well the little creatures are doing, and what type they are.

            Often little ecosystems build up step by step, Stage 2 animals (bacteria, insects, whatever) only move in once Stage 1 have set things up for them. This applies to tooth decay, which has a complex set of symbiotic microbes, some of which can only live on top of others. It also applies to decomposing murder victims, as body farms have discovered, you can tell a lot about timing by studying the life stages of the particular insects, that all arrive in their turn.

            This might all be interesting in studying exactly how PLA breaks down. Or it might not.

          2. Just don’t use subjective analysis if at all avoidable.
            Fracture tests, reflectance, yield strength. All quantitative analyses that don’t require much equipment. If you can quantify polymer breakdown, great, buy I imagine that’s out of most hobbyists ability.
            Even a simple rating of angular features would be easily replicable between two people.

            Blinding won’t make a poorly designed experiment work better.

    2. I printed end-caps for a pump filter assembly where the end caps were 4″ diameter and had openings on them for water to pass through. I installed it in a lake where we were pulling irrigation water from and used it for 2-3 years. I later replaced the filter with another design and the original PLA pieces were still pretty much the same as they were when I installed them (outside of the usual staining and bio mass build up). It didn’t look very biodegradable to me, even with water flowing across it every day for 2+ years.

  1. I can’t help to think that if you place PLA in a compost type of situation that it would degrade way faster than sitting on top of say, the lawn. The shape and number of attack surfaces is probably also important.
    I get my thinking from that the filter basket on the fish tank is a really active bacterial environment (lots of air and water) and has allot of attack surfaces but cap in the water has way less attack surfaces and a less bacterially active environment.

    1. Obviously , nobody reads much into the texts that suggest PLA is biodegradable. In almost everything I have read , it states that it is biodegradable in INDUSTRIAL COMPOSTERS , and not so much naturally. It does happen in a natural biologic environment , albeit very slowly. Its likely to degrade faster via UV/thermal degradation than biologic decomposition in a natural environment.

      Keep in mind , aquariums typically use lighting that would tend to degrade plastics faster.

      1. Has anyone actually bothered to read the spec documents on PLA? There’s no need to speculate. There are official instructions on the disposal of PLA via composing, as well as descriptions of the decomposition mechanisms (hint: It needs soil bacteria that can beak down and metabolize lactic acid into CO2, water and Humus). Like many other biodegradable plastics, it has to be exposed to intense heat for a prolonged period. Off the top of my head, I believe it’s supposed to be tat the center of an industrial compost heap for something like ten days, at a few hundred C.

        1. Maybe 40-50C (perfect for heat-loving microorganisms), not a few hundred C. Temperatures that high would kill bugs quite quickly.

          PLA will degrade if heated to a few hundred degrees C “dry”, but that’s a different mechanism.

          1. Right, I’m referring not so much to burning in air, but heating it in a closed inert atmosphere. It’ll degrade back to lactide monomer under those conditions.

        2. An industrial compost heap is NOT the same as an industrial “composter”. There are “machines” that take over and do natures part and can get the job done faster. However,whats the point in that really. We can “recycle” non-biodegradable plastics in similar type of machinery , so saying we can stick PLA in a machine composter isnt saying much other than there is no potentially toxic byproduct of the material itself , but not necessarily from the process.

      2. The compost I was thinking of is the one in my parents back yard. I have not take the temperature of it but I am guessing that it is nice and warm and wet and filled with bacteria that could eat the pla up over a month or two. That would probably be considered consumer biodegradable, since the time frame for that kind of compost is next spring here in Scandinavia.

  2. I’ve got a number of small PLA busts that failed on the dome of the skulls. I sliced them off at the forehead and planted stuff in them – 2 years exposure to UK weather extremes and constant moisture – they have gathered moss but are perfectly intact.

        1. I think [jelle] is wondering how it is known that the objects in question are ‘intact’, I guess they could have begun to degrade internally without any outward sign.

    1. Indeed. According to our chemists at Ultimaker. It breaks down, under certain conditions. Conditions which are easier to reach then most plastics. But does not mean it’s biodegradable as some people would think. (Which can be seen as a positive and negative thing)

  3. As far as I have heard about PLA is, yes its biodegradable, but in a high temperature compost machine. so not a regular garden compost pile.(where it will sit for quite some time without an issue)
    Not sure what the useful difference at that point would be compared to an incinerator.

    I verified on the wiki, but cannot find the reference to that anymore.

    1. If you know how to manage a compost pile, you can compost PLA. I do it. Although since my pile is small (few m^3 and its cold here it generally takes a year (same as sticks and woody garden bits) Industrial compost piles, like our municipal composting program, are large piles, well-managed, maintain high temperatures, and can break down PLA very fast. You don’t need a machine You need a big pile to hold high temps and regular turning over.

  4. From a chemist’s viewpoint PLA is an ester and can be hydrolyzed to lactic acid under basic conditions. Whether PLA degrades depends a lot on temperature, presence of moisture and pH of the solution. PLA is also being used in biodegradable implants. GGL and you’ll find all details.

  5. PLA may or may not be biodegradable depending on the method of disposal and the time involved, rather than how or where it’s in use. The FTC oversees this as a deceptive labeling practice rather than, say, the EPA who are more interested in what might get into the groundwater or soil.

    In the US, with “biodegradable” items:

    “It is deceptive to make an unqualified degradable claim for items entering the solid waste stream if the items do not completely decompose within one year after customary disposal.”
    (https://www.law.cornell.edu/cfr/text/16/260.8)

    The one-year time horizon has been pushed back by a couple of challenges since most material doesn’t substantially degrade in sealed landfills (it does dehydrate and there is substantial compaction) and there’s no standard test method for it, so this is still in limbo.

    https://www.iplitigationcurrent.com/2015/02/26/ftc-fails-to-prove-green-guides-meaning-of-biodegradable/

  6. I’m curious if the plastic is actually breaking down, or breaking into smaller pieces and introducing the PLA equivalent of microspheres into the water supply. More of a pollutant than green.

    1. no, it actually degrades down to individual monomers that are soluble in water (and not solid particles). Depending on the PLA, these are used in metabolic processes in the body or somebody. That is why the bio part is important. All plastics will degrade via UV or thermal processes over time. Only the bio ones will naturally, effectively go away.

    1. I remember Flux magazine in the 90s telling readers that if you put methylene blue in someone’s cola it would make their urine blue without them knowing how. Different times…

      1. It would also dye the whites of their eyes over prolonged exposure. It was given to sailors as medicine.

        And it was used to monitor that mental health patients keep taking their pills.

    1. I suspect you were meaning this as a joke, but there are a number of cases where some chemical was being dumped into the environment and was considered a persistent pollutant… only to disappear years later when microbes finally figured out how the chemical was food. I wish I had a good link for this right now.

    2. I know someone whos master thesis was about how to biodegrade the epoxy in carbon fiber parts.
      In a couple of years this could be THE method for recycling CF-Parts (like car- or airplane-Parts)

  7. Things don’t decompose very fast, if at all, in a landfill. They’ve dug up newsprint, still readable. Old shoes, not much past what they were when they went in.

    http://science.howstuffworks.com/environmental/green-science/landfill7.htm

    A place I worked was built on partly on an old garbage dump, and the foundations required sampling every so often which brought up various interesting items such as shoes. Nothing much happens to stuff when you bury it.

    1. My school was build on garbage dump that was moved out from downtown. Each year we were cleaning the area around it for Earth Day or something. So we dug out few things, including spent shotgun cartridges, which is curious because my country has very strict laws when it comes to owning a gun. Still after at least 35 years in damp earth paper they were made off was undamaged, but brass part was tarnished..

  8. Interesting. However, I wouldn’t say that sitting in a jar of water for 3 years is indicative of biologic degradation. PLA doesn’t just dissolve in water as one might expect. You really need to have some biologic system there with cells, enzymes, etc to facilitate the breakdown. We aren’t talking just about the sun and UV breaking down plastics, any of the plastics will succumb to UV at some point. Being biodegradable means that biologic systems can interact with the material. Check out this link – good info for those concerned or interested…
    https://www.researchgate.net/profile/Aamer_Shah/publication/5515372_Biological_degradation_of_plastics_a_comprehensive_review/links/02e7e52ac0f0e996d0000000.pdf

  9. Hello!

    I researched the toughening of PLA and did subsequent biodegradation studies in my undergrad for a year (after working with siloxanes for two). To answer the question, we know for sure PLA is biodegradable. I’m talking pure PLA, which isn’t necessarily what you are buying when you get a spool of resin. Most fillers are minerals, so it doesn’t matter anyway, but people should know that PLA can have fillers and processing aids. JonCryl, for example, is a chain extender and processing aid used in higher molecular weight PLAs or PLA copolymers that tries to undo chain scission of PLA under processing conditions.

    PLA degrades very easily at temperatures near its melt. I’ve put neat 3051D PLA through an extruder and watched it come out with roughly 60% of its molecular weight. PLA undergoes hydrolytic degradation and chain scission at very slow rates at ambient temperature. There are two methods that the PLA chain can split, it can split due to an oxygen exchange at the C=O site, causing a split into two identical polymers of different molecular weights OR you can get a hydrogen transfer which is less common in this context of biodegradation, and the hydrolytic route is more talked about. Eventually, you would in theory get complete depolymerization back to lactic acid. Eventually.

    Anyway, point is, relative humidity, pH, and temperature are all important variables when we are talking about PLA degradation. Combined with the fact that some of these polymer chains are of quite high molecular weight and most models are at least a few dozen grams, I’m not surprised that sitting in a cupboard it won’t noticeably degrade. I mean, technically it is, but the kinetics would be so slow at room temp in dry air… Even it water it could take years depending on temperature, pH and PLA molecular weight. If its a copolymer who knows!

    Moral of the story, yes, PLA is highly researched and been proven to biodegrade as a polymer. All structures made of PLA would biodegrade eventually, however, that could mean thousands of years for certain structures. Thinner things, like bags, would probably degrade faster than a solid cube would, for example. Also, there is a huge difference between biodegradeable, biocompostable, and biobased. But that’s a whole extra can of worms.

    Would you like to know more?

    http://www.alplastics.net/Portals/0/Files/Summer%20school%20presentations/ALPLastics_polymer_stability_and_degradation.pdf

    http://www.ncbi.nlm.nih.gov/pubmed/9622536

    1. Nice summary. In the case of the MW loss in your extruded PLA experiment, which I assume was carried out “dry and hot”, it’s likely that it’s not hydrolyzing but rather depolymerizing back to lactide (the ring-opening reaction operating in reverse). It’s a surprisingly easy reaction.

      1. We never controlled for moisture, so it was actually a blend of both! You can see that in DSC and IR pretty well. It’s just that the decomposition was so little and we had additives to build it back up anyway, so it wasn’t worth trying to bring the moisture down. PLA was dried, but then again its quenched in a water bath, so it’s exchanging one water source for another!

  10. biodegradable is not the same as compostable.

    I’ve never heard any reputable source say PLA was biodegradable, but many said it is compostable.

    Compost breaks down in the presences of heat oxygen and certain types of bacteria, worms, etc.

    Under water there isn’t particularly much oxygen.

    1. Water is made of oxygen and hydrogen, if that’s what you mean, but the O in H2O isn’t available to react with other atoms unless you put a large amount of energy into separating it from the H2 part.

      1. No, but all “living” water, with fish and microbes and stuff, has to contain dissolved oxygen, or else they couldn’t breathe.

        Stagnant water, not so much. It depends on either plant life, or the churning action of moving water, to get the oxygen in. Plants include phytoplankton.

        1. There is an amazing world of microbial life that does not require oxgen. Most microbes are anaerobes, they grow when oxygen is not present. For many types of microbes, such as methanogens, iron reducers, sulfate reducers, and obligate anaerobic fermentors among others, oxygen prevents growth of any kind. These are really neat forms of life, and are important in biodegreation of many compounds.

          I would guess from the structure of PLA that it degrades by biotic activity by 1) free radical chemistry of the white rot fungi (quickly), 2) enzymatic degredation and complete mineralization by aerobic consortia, and 3) (possably very slow) degredation by anaerobic microorganisms.

  11. My housemate and I decided to do such an experiment. Some of my PLA scraps were placed in the dirt beneath a concrete slab in our back garden, almost a year later they are still there. A single extruded strip and part of a failed print were placed under the slab. I haven’t inspected them closely, but they do not appear to have degraded in any significant way from cursory inspection just lifting the slab.

  12. Industrial polymer chemist here.

    Biodegradability is not a binary thing — there are a bunch of potential mechanisms, things can be “more” or “less” biodegradable, and there are specific well-defined tests (ASTM) to put numbers on the whole thing.

    Based on my experiences, PLA will undergo chemical degradation quite efficiently under the following conditions:

    – in an industrial composting facility (hot and humid, lots of microorganisms) — the polymer ultimately becomes hydrolyzed back to lactic acid, which is then metabolized to CO2.

    – in alkaline or acidic conditions, where the PLA either hydrolyzes to lactic acid or depolymerizes to lactide (the monomer from which PLA is derived), depending on conditions.

    In practice, an actual PLA object placed in this type of environment will appear to more or less “fall apart” (disintegrate) into smaller pieces, which will in turn disappear as they are completely degraded. Degradation time depends on exposed surface area and how well the surface is wetted. For many applications (e.g., resorbable sutures made of PLA copolymers) this degradation time is well worked out, but for random 3D-printed parts things would probably be quite variable.

  13. Folks, newspaper is definitively biodegradable; however, it isn’t tough to dig through a landfill and find paper 3+ years old. The speed with which something degrades varies considerably with its disposal method. PLA will biodegrade, while most synthetic based plastics will not (or will take orders of magnitude more time to do so).

  14. http://www.greenfacts.org/en/marine-litter/l-2/3-micro-plastics.htm

    +1 vote for the hypothesis that the breakdown of a filter, exposed to relatively-rapid and continuous water flow, can likely be attributed to mechanical-degrading rather than bio-degrading.

    Two key elements need to be demonstrated to make a claim of biodegradability:
    1) The PLA underwent a CHEMICAL change, it didn’t simply break apart into smaller pieces. My glass window does not biodegrade when struck by a baseball.

    2) If a chemical change can be shown, then it must further be demonstrated that a biological agent was responsible for the change. There’s nothing “bio” about using gasoline as a solvent to dissolve rubber, styrofoam, etc.

  15. Look at its certification. ASTM 6400. it says it will compost in a commercial and municipal compost in 180 days. It will NOT break down in a backyard compost as there is not enough moisture, heat, and aeration. It will not break down in a landfill. However, the FTC has decided that plastics that compost should be called biodegradable as they need to break down in a year or less. This just shows how much the FTC knows. By the way they got this definition by googling people and getting their responses, not by looking it up in a dictionary or asking someone in plastics. I have heard stories of PLA melting down in high heat or in direct sunlight, but not completely going away. Just enough to leave a big glob. However, I have heard that many of the tests done on PLA were with PLA in a powder form, not the actual product, like a cup. This is an unsubstantiated rumor, but I have been told by several commercial composters that they do not accept PLA anymore as it is not completely breaking down. By the way, paper is compostable, not landfill biodegradable. Dr. Rathje, a well known anthropologist studied landfills and found papers 50 years old and readable.

  16. Thanks Caleb !

    I just want to point out that hackers have to stay…. hackers…they are not science people’s ! :) !

    But what the difference then !? Sometimes: not a big one (even more if we look at the superb articles in this website!), but more often: a job ! Years of studying (yes it is painful and long) and at the end for example: you cannot do your plombery by yourself so you do not try to give to your plombery advice without knowledge (and a lot of studying !)!

    Yes buruing staff in water can be a good experiment to know if something is biodegradable… And humans invented science and science made them clever and they made more research and cool stuff and cool research and after buruing stuff in water they did more ! And knows more ! And voilà ! What a wonderful world :) if every one stay to there place, mostly ;)

    So just to say that we are living in a wonderful work, us hackers, but let’s respect the other people in their knowledge and being. Before doing thing, be aware of what is existing and why it is like that. Explain what you learned and on this base explain what you thing, like a science guy. It is pain in the a** but it is why the world is like that ;)

    On that, sorry for my french-english :)

  17. PLA is used for dissolveable surgical implants.
    Reference: https://books.google.com/books?id=mbdgBAFV2YwC&lpg=PA132&ots=LFdMCeriDr&dq=surgical%20pla&pg=PA131#v=onepage&q&f=false

    While I have never personally seen PLA break down, something definitely happens to it as it gets old. Not sure if this is due to hygroscopy or UV exposure, but it can get very brittle. So brittle that it can’t even be unwound from the spool without snapping.

  18. This was always my beef with Mythbusters (RIP). If you are educated in chemistry then you know that PLA will absolutely biodegrade under the correct conditions. No need to test it out. It’s a polyester and there are numerous biological and chemical processes that will cause it to degrade. The physical form will have a huge impact. Steel filings will degrade overnight while a steel beam will last– exposed to the elements– for years.

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