This is a common misconception. PLA is technically compostable industrially, but it will be very slow to break down naturally if you just leave it outside. It can take about 80 years, which is a lot better than other plastics, but it’s a bit misleading that it’s called biodegradable. There are true biodegradable filaments like PHA, but they’re a lot less common.
That being said, 3D printing is actually really useful, and not a significant part of the plastic waste problem.
There’s some confusion about how PLA breaks down because there’s remnants after the 3-5 years where it’s not detectable anymore. Those remnants are not microplastics at that point. They’re just the base components (e.g. lactic acid) that can last a little bit longer.
Some colorants can last a really long time but I haven’t looked into those as much as I have plastics.
BTW: The “sparkly bits” in “silk” filament is just mica powder (iron). It looks like it might be harmful but it’s not.
It wouldn’t surprise me if the science on this is divided, especially because conditions (and the shape of the object) vary so much. It seems very plausible that a thin injection molded PLA cup could break down really fast in a sunny pond in a warm climate, but a thick 3D printed object buried in the ground somewhere with a cold clinate could take many decades.
Anyway, it sounds like it’s maybe not as bad as I thought, but it’s still not good to treat it like typical biodegradable materials. Especially when pla microplastics are still harmful despite being shorter lived.
A 3D printed PLA object would degrade faster than an injection molded one. Because the layer lines provide much, much more surface area for bacterial infiltration.
I read a study about that specific thing once but I searched just now and can’t find it (from my phone). I’ll search again when I’m back at my PC later so I can give you a link but… That makes sense, right?
For plastics like PET and ABS microbial breakdown doesn’t occur but with PLA and PHA it does. The more surface area, the faster it can be broken down.
Whereas with ABS and PET, the more surface area, the faster it will turn into long-lasting microplastics.
This is a common misconception. PLA is technically compostable industrially, but it will be very slow to break down naturally if you just leave it outside. It can take about 80 years, which is a lot better than other plastics, but it’s a bit misleading that it’s called biodegradable. There are true biodegradable filaments like PHA, but they’re a lot less common.
That being said, 3D printing is actually really useful, and not a significant part of the plastic waste problem.
PLA microplastics take three years. That 80-years figure you’ve got in your brain is for PET:
https://www.sciencedirect.com/science/article/abs/pii/S0166445X25001547#%3A~%3Atext=In+fact%2C+slower+degradation+rates%2C(European+Bioplastics%2C+2023).
(BTW: That study is brand new! From a few days ago.)
See also: https://cen.acs.org/materials/polymers/biodegradable-polymers-make-microplastics/102/i37#%3A~%3Atext=In+the+open+environment%2C+PLA%2Cover+another+several+years+(Sci.
There’s some confusion about how PLA breaks down because there’s remnants after the 3-5 years where it’s not detectable anymore. Those remnants are not microplastics at that point. They’re just the base components (e.g. lactic acid) that can last a little bit longer.
Some colorants can last a really long time but I haven’t looked into those as much as I have plastics.
BTW: The “sparkly bits” in “silk” filament is just mica powder (iron). It looks like it might be harmful but it’s not.
I think the 80 year figure was for PLA, as PET lasts well into the 100s of years (450 is the number I’ve seen)
This article claims 80 years https://3dinsider.com/is-pla-biodegradable/ but I haven’t taken the time to do proper research about this.
It wouldn’t surprise me if the science on this is divided, especially because conditions (and the shape of the object) vary so much. It seems very plausible that a thin injection molded PLA cup could break down really fast in a sunny pond in a warm climate, but a thick 3D printed object buried in the ground somewhere with a cold clinate could take many decades.
Anyway, it sounds like it’s maybe not as bad as I thought, but it’s still not good to treat it like typical biodegradable materials. Especially when pla microplastics are still harmful despite being shorter lived.
A 3D printed PLA object would degrade faster than an injection molded one. Because the layer lines provide much, much more surface area for bacterial infiltration.
I read a study about that specific thing once but I searched just now and can’t find it (from my phone). I’ll search again when I’m back at my PC later so I can give you a link but… That makes sense, right?
For plastics like PET and ABS microbial breakdown doesn’t occur but with PLA and PHA it does. The more surface area, the faster it can be broken down.
Whereas with ABS and PET, the more surface area, the faster it will turn into long-lasting microplastics.