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. 

 

 

 


5 comments

  • 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

  • Soumyakant

    Being able to degrade into innocuous lactic acid, PLA is used as medical implants in the form of anchors, screws, plates, pins, rods, and as a mesh.23 Depending on the exact type used, it breaks down inside the body within 6 months to 2 years. This gradual degradation is desirable for a support structure, because it gradually transfers the load to the body (e.g. the bone) as that area heals. The strength characteristics of PLA and PLLA implants are well documented.
    Source: https://en.wikipedia.org/wiki/Polylactic_acid

  • Meredith

    I would note that it is compostable in commercial composting facilities, like we have in Seattle. This makes it a much greener material than ABS.

  • Steve

    I didn’t realize it took so long to decompose and how misleading the claims were. I’m wondering if the pla prints degrade with absorption of water faster than abs. Thanks for enlightening me.

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