PLA use outdoors? – 3D Printing Stack Exchange
Posted by jpluimers on 2021/07/05
[WayBack] PLA use outdoors? – 3D Printing Stack Exchange:
TL;DR: though bio-degradable, PLA needs high temperatures (> 50 Celsius) to degrade.
So in European summers, for light weight enclosures (like weather stations or signage), it should be fine.
- [WayBack] Using PLA for Long-Term Outdoor Applications – IEPAS
To biodegrade within 90 days, as described, the products have to reach 140 F for 10 consecutive days. This requires a special facility, which few consumers have access to. If your PLA products end up at the landfill, they will not degrade any faster than a petroleum-based product.
- [WayBack] Polylactic acid: Degradation – Wikipedia
Abiotic PLA degradation is due to 3 mechanisms:[35]
- Hydrolysis: The ester groups of the main chain are cleaved, dividing the molecule in two parts, thus reducing molecular weight.
- Thermal degradation: A complex phenomenon leading to the appearance of different compounds such as lighter molecules and linear and cyclic oligomers with different Mw, and lactide.
- Photodegradation: Sunlight induces degradation due to low-wavelength and high-energy UV radiation. This is a factor mainly where PLA is exposed to sunlight in its applications in plasticulture, packaging containers and films.
The hydrolytic reaction is:
{\displaystyle {\ce {-COO + H2O -> – COOH + -OH-}}}
The degradation rate is very slow in ambient temperatures. A 2017 study found that at 25 °C in seawater, PLA showed no degradation over a year.[36]
Pure PLA foams undergo selective hydrolysis when placed in an environment of Dulbecco’s modified Eagle’s medium (DMEM) supplemented with fetal bovine serum (FBS) (a solution mimicking body fluid). After 30 days of submersion in DMEM+FBS, a PLLA scaffold lost about 20% of its weight.[37]
PLA samples of varying molecular weight were degraded into methyl lactate (a green solvent) by using a metal complex catalyst.[38]
Some bacteria can also degrade PLA, such as Amycolatopsis and Saccharothrix. A purified protease from Amycolatopsis sp., PLA depolymerase, can also degrade PLA. Enzymes such as pronase and most effectively proteinase K from Tritirachium album degrade PLA.[39]
Degradation is the reverse of the synthesis process in this Wikipedia picture:
For other materials and in-car usage, read:
- [WayBack] material – 3d printing for outdoor use: what types of filament are most weather resistant? – 3D Printing Stack Exchange
- [WayBack] filament choice – Can you put PLA parts in your car (in the sun)? – 3D Printing Stack Exchange
generally, materials should not be exposed prolonged periods of time above (give or take):
- 70 °C (158 °F) for basic Co-Polymers
- 85 °C (185 °F) for ABS
- 100 °C (212 °F) for enhanced Co-Polymers
- 105 °C (221 °F) for Polypropylene (PP)
- 110 °C (230 °F) for Polycarbonate (PC)
…
If you put PLA parts in a sealed plastic bag (or two to keep it dry) and simmer in water (212 °F or 100 °C), the part “anneals”. The time taken varies with the part shape, but for small parts should be about 15-30 minutes. You can simmer longer if unsure, but it provides no additional benefit once the part is annealed. When you remove and cool the annealed part, it will feel harder and more compact. You may also notice a slight hazing or color change.
Annealed parts become a bit more resistant to heat warp. The annealing process shrinks and hardens your part (I’ve annealed gears) so you need to account for the shrinkage by making the unannealed part slightly larger.
–jeroen
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