The Misleading Biodegradability of PLA

Biodegradable PLA

 

The vast majority of FDM (fused deposition modeling) 3D printers primarily consume ABS or PLA filament. ABS, a petroleum based thermoplastic, is a little tougher and bit more flexible than PLA, but also a little more finicky to print with. ABS generally requires a heated bed to reduce warpage, and also emits a potentially troublesome scent as it is extruded. PLA on the other hand, or poly lactic acid, is derived from starchy sources - most often sugarcane or corn starch and has a far more palatable (some note a breakfast waffle-like) scent when extruded.

The marketing writes itself. PLA is a natural, bio based alternative to petroleum laden ABS!  Sounds (and smells) like you could eat it! I'm a hands on guy so I tried a nib, tastes like plastic. The baked out, boiled down, unsweetened truth is that it is indeed, plastic. Marketeers love to tout the biodegradability of the material, and its true, that at some point it will biodegrade. The reality however, is that this process will take several hundred years in a typical landfill. To biodegrade, PLA requires a laundry list of conditions to effectively break down. Specifically - oxygen, a temperature of 140+ degrees, and a 2/3 cocktail of organic substrate. Collectively, these are absent in any scenario outside of industrial composting facilities. This means that PLA plastic will sit in that landfill right alongside ABS and other plastics for a very long time.

When considering the environmental friendliness of a particular product, it is essential to consider the amount of energy used to create that product. For all plastics, the energy required is particularly significant. This dictates that the ultimate waste of that energy is to literally discard it. For this reason, keeping the material in its intended physical form is far more responsible. 

What do we propose? Print responsibly and recycle accordingly. The Filabot, for lack of a better engineered example, is capable of turning your old PLA or ABS prints into fresh filament again so you can indefinitely extend the practical life of the material. Plastic, once it has been industrially produced, is categorically best staying plastic. Giving this plastic renewed purpose is the key, and is ultimately a far more productive future than an impractically slow death in the ground. 

 

 

 


8 comments

  • Jim

    > The EU standard EN 13432 mandates: Disintegration [..] composted with biowaste for
    3 months. After this time, the mass [..]

    What is this a mandate for? For being able to say something is “compost-able”, rather than “recyclable”? Surely it wouldn’t mean that you couldn’t say (presumably in fewer words), “is recyclable into biomatter in a proper waste processing facility that uses appropriate shredding technology, pre-treatment, filtering, and long-duration microbial bio-processing”

  • iksea

    I have investigated PLA compostability for work projects in the past and dug into understanding what BPI and Cedar Grove (PNW compost facility) are looking for to certify a polymer or fiber based product to be compostable. The reality is that you may want your PLA 3D prints to compost, but they will not in the commercial facilities because they have too thick of wall sections to degrade in the batch time of the process. Most systems use 12 weeks or so to break down and if the wall sections are too thick, this will not happen. This is what made it hard to come up with compostable forks/spoons initially since you need some thicker sections for strength. Because most 3D prints are much larger/thicker than utensil wall thicknesses, they most likely will not compost in the time allowed and will be screened out with the rest of the contaminates and sent to the landfill. The only way to ensure that composting could happen would be to shred your parts into fine shavings (<.06") before sending to the compost. Another issue would be that the colors and additives are most likely not food safe and would most likely contribute to chemical contamination unless specifically formulated for this purpose. Look up PFAS and BPA chemical contamination of compost from migration from treated paper products. Another toxic mess building up.

    The EU standard EN 13432 mandates:
    Disintegration, namely fragmentation and loss of visibility in the final
    compost – this is measured in a pilot composting test (EN 14045) in
    which specimens of the test material are composted with biowaste for
    3 months. After this time, the mass of test material residues has to
    amount to less than 10% of the original mass.

    https://docs.european-bioplastics.org/publications/bp/EUBP_BP_En_13432.pdf

  • Adam

    PLA can be composted in commercial composting facilities. It is a much more renewable plastic for 3D printing than ABS.

  • Me

    Compare hundreds of years for decomposition of PLA to effectively “never” for ABS. True, PLA may take a while, but it’s still a vast improvement over ABS. And less toxic than ABS if ingested by marine organisms. It’s not perfect, but it’s a step in the right direction.

  • Mihaela

    I’ve also been looking at the biodegradability of PLA for printing art for my home, and came across this research study commissioned by the California Department of Resources Recycling and Recovery and produced by California State University in Chico: http://www.calrecycle.ca.gov/publications/Documents/1435%5C20121435.pdf

    Long story short: PLA doesn’t degrade under any measurable criteria in 365 days in a simulated marine environment, complete with sand, microbiota, 30 deg. C, etc.

    For PLA degradation in landfill environments:
    http://www.material.chula.ac.th/Journal/v18-2-2/83-87%20RUDEEKIT.pdf
    Not much degradation there either.

    A generic biodegradable polymer review article that includes a short paragraph about PLA and acknowledges (somewhat by omission) that it is only biodegradable in industrial composting facilities (by and large missing in any major US city I’ve lived in):

    http://homepages.rpi.edu/~grossr/_doc/publication/SCIENCE%202002%20297%20803.pdf

    and another, highly cited one:
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769161/pdf/ijms-10-03722.pdf (skip to this one first if you are a science geek and want to have a bit of perspective on plastics; not all plastics are equally bad, and PLA is by far NOT the most biodegradable one.)

    Scientific American thinks that a PLA bottle will biodegrade, yes, but it will take between one hundred to one thousand years, in a landfill environment:
    https://www.scientificamerican.com/article/environmental-impact-of-corn-based-plastics/

    The plastics of choice for good biodegradability in landfill conditions, seem to be PHB, poly(hydroxybutyrate), which is bio-based, and PCL, poly(caprolactone), which is (surprise !) petroleum-based. From here on I ran out of breath, but the next logical step would be to investigate where we can access 3D printers that use these two friendlier plastics for home projects. Please write to me at the address above if you have the answer. I wish you happy and thoughtful printing :)
    M

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