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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]

    1. Hydrolysis: The ester groups of the main chain are cleaved, dividing the molecule in two parts, thus reducing molecular weight.
    2. 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.
    3. 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:

–jeroen

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