Recycling Plastic With Liquid Nitrogen

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Recycling 3D printer filament isn’t a new idea, and in fact there are quite a few devices out there that will take chunks ABS, PLA, or just about any other thermoplastic and turn them into printer filament. The problem comes when someone mentions recycling plastic parts and turning them into filament ready to be used again. Plastics can only be recycled so many times, and there’s also the problem of grinding up your octopodes and companion cubes into something a filament extruder will accept.

The solution, it appears, is to freeze the plastic parts to be recycled before grinding them up. Chopping up plastic parts at room temperature imparts a lot of energy into the plastic before breaking. Freezing the parts to below their brittle transition temperature means the resulting chips will have clean cuts, something much more amenable to the mechanics of filament extruders.

The setup for this experiment consisted of cooling PLA plastic with liquid nitrogen and putting the frozen parts in a cheap, As Seen On TV blender. The resulting chips were smaller than the plastic pellets found in injection molding manufacturing plants, but will feed into the extruder well enough.

Liquid nitrogen might be overkill in this case; the goal is to cool the plastic down below its brittle transition temperature, which for most plastics is about -40° (420° R). Dry ice will do the job just as well, and is also available at most Walmarts.



		

Comments

  1. carbohydrates says:

    Please don’t shop at Walmart.

  2. joho says:

    what are this temperature grades? -40*F or -40*C and what is 430*R??? 420°K? i don’t think so… what about si? the whole world uses it…

  3. The fact that this post has a temperature in Rankine makes me very happy.

  4. ANC says:

    -40°?! Wahh, what is that in Celsius?

  5. john smith says:

    I love the fact that you just left that hanging as -40, because it’s the one temperature where you don’t need to qualify it.

    I would think the main thing with recycling plastics is mixing in fresh pellets with the recyled stuff. That’s how the pros do it.

  6. pcf11 says:

    Forty below? That calls for the Rodeo Song!

  7. Sven says:

    Funny… not a single comment relates to the actual content of the article…

    I am wondering if instead of cooling the plastic before cutting it, one might heat it up to near melting point to achieve almost the same effect.

    • Heph says:

      In what? I wouldnt suppose you ruin a perfetly good cooking pot to kill a simple juice-bottle. For me it would be question of Formfactor and energy. Having a to big melting device would be unsustainable (at least here where energy prices are high) because you throw away tons of the energy you intend to use for the melting.

      If you have a filabot or something like it you only need to melt the part of the plastic that gets added to the end of the newish filament. For this having uniformly small flackes or even dust would be perfect because that leaves less space for air.

      I personaly wouldnt use the same blender for the Plastics and food though.

  8. My technique involves chucking all my scraps in a pot and heating it all up into one large chunk / glob. Run this through the table wood router. It carves it into beautiful little small uniform shavings. I have me a bucket of them. Just don’t have a filament extruder just yet so can’t tell you how that goes.

  9. Taylorian says:

    for cooling purposes I would try to source CO2 for welding. Rig up a holder that can be flooded with the liquid from this and you basically have liquid dry ice. fairly cheap and damn quick.Take care to provide adequate ventilation.

    When not cooling your plastic, could double as an quick beer chiller…just saying.

  10. daewootech says:

    im sure freezing it helps, but beware i already shattered two cups in that blender, when the blade hits the plastic, especially larger chunks and slams it against the wall it either shoots a hole out the side or cracks the whole container.

  11. Kronk5 says:

    * doesn’t the liquid nitrogen (or even dry ice) push the total cost above that of filament?
    * Most Walmart stores in the US sell CO2 dry ice??? really??

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