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How long should you cook PLA filament ?

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  • How long should you cook PLA filament ?

    I didn't really cook it because it would probably taste awful and be quite gooey but I was attempting to revive a filament that I had given up on a long time ago. In fact I had two filaments from the same company 3D Solutions that gave me trouble. The clear roll is (was) incredibly brittle but I had stuck all my problem filaments into my food dehydrator long ago and decide to try them again. The clear one printed ok till it got down into the roll and then just shattered in about 5 pieces inside the Bowden tube. I couldn't believe how brittle it was. worse than before. After a couple of hours in the drier it is printing nicely and is no where as brittle.

    The flesh coloured roll which was always plugging and under-extruding printed a new xyz cube design that astonished me.
    Notice how there is a tiny bit of fuzz above the Y but I am astonished it printed this test that well what do you think. Sorry if the photos aren't great I'm trying to learn how to use my cel camera. since I now have a cel phone for the first time.

    I had to delete one side.


  • #2
    I think a good way to store filament is to dry it in your dehydrator for a couple of days, then transfer it to a sealed container with a container of silica gel. For containers you can use strong plastic bags, but I think Tupperware style sealed containers would be better. I think it's worth getting some of the indicator silica gel from Amazon. It can tell you when the gel needs baking in the oven to refresh it.

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    • #3
      This had much less to do with drying than changing the composition of the filament. The change was incredible for this particular filament. It would break like uncooked spaghetti in my hands before I 'cooked' it and after it was as flexible as any other PLA filament. Quite interesting.
      I think I am printing the clear too hot but I shall certainly experiment with it. I really wonder how it got so brittle. I wonder if their company is still functioning even though I still see it for sale on Amazon.
      Obviously the first time I dried this filament it only penetrated so far.

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      • #4
        I'm sorry, but I don't agree. I believe it is about moisture. A feed dehydrator can't really cook filament, but it certainly can dry it. I think you dried it and that's why it became flexible. It got so brittle because it absorbed a lot of water and retained it for a lengthy time.

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        • #5
          I think we actually agree. Yes it did dry it, but I think that changed the whole composition. I would guess heat more than just drying. But of course that remains to be proved. Could we prove one way or the other? What kind of test could we do?

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          • #6
            It really is the moisture but, yes, it changes the structure of the filament. I haven't been able to find out exactly what's going on, but I would not be surprised to learn that the water cross-links some of the molecules together, making them more rigid and less pliable. Perhaps the heat really just overcomes those bonds and frees the water from the filament again. With the H2O gone, maybe it allows the filament molecules to flex more.

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            • #7
              I'm not sure that it values future studies. This is a one of a kind deal as far as I know filaments. Which isn't too far. I think the transformation of this material is so extreme that it bears further study.

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              • #8
                The temperature is key here. For example PLA starts softening at around 50°C. So you don't want to be that high as it slowly turns your spool of filament into a block of filament.

                A filament heater with a fan is best. Here you can go up with the temperature a little as the hot air is not stuck, but can leave the casing as steam taking the water out. This is what you want. So the ambient temperature inside is not a high as hot air is leaving and cold air is getting to temperature. Kind of a hot summer wind, which makes your skin dry, while without wind the effect is much slower.

                An oven with a circular fan is heating with a constant energy, but the air inside is stuck and heating over that point. Kind of like feeding hot water into a coffee maker. It will break. Also the moister is caught inside, so it does not help removing it, when it drips down back onto the filament.

                You used a food dehydrator, which I also do. Make sure the hot air is not just inside the chamber, but can also flow around. I had to print a little stand for the filament, so the hot air goes through the middle of the spool and around it. I also drilled 8mm holes into the top, so the air can go out fast.

                Here is my project in case you missed it: https://www.thingiverse.com/thing:4578549

                Before testing a spool I would recommend using 100mm of filament placed vertically and do a test run. It should not bend or give in. Repeat the process until you find the spot for your filament.

                To obtain the amount of time the dehydration needs to run, simply measure the weight of the spool before and every hour during the process. This way you get a curve and can see how long you need to have the spool in there and at which point the water removal is so low, that it makes no sense (energy efficiency) to continue the process.

                Speaking of brittle filament:

                I keep all my filament in the open. I use the dryer just for TPU. I noticed that the longer the filament is in the open, the more brittle it gets. BUT the water is not getting everywhere. In my experience at least for ABS and PLA the water gets in from the cutting point. I usually need to cut away 50 to 100mm until I get a flex area again, which is less brittle and has normal properties again. Of course you could prevent that by proper storage or drying, but since here is the humidity not a problem and the cutting off a section is only needed after around 6 month, at least for me this is fine.

                e.g. in Florida you need proper storage and drying for sure. In Germany not so much. Especially when you store your stuff in a normal heated house and not a cold basement or a garage, where the temperature is fluctuating.
                Last edited by Geit; 01-28-2022, 07:56 AM.

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                • #9
                  I have a couple of SunLu dryers that seem to work pretty well. I keep a small hygrometer in them to monitor the humidity. Of course, I also have all the PrintDry vacuum containers I've posted about that keep the filament dry. They each have a small hygrometer in them.

                  I've actually had brand new spools of filament that were completely vacuum sealed but still the 1st half inch of the end of the filament was brittle. Of course I just cut off an inch and move on, but it's interesting that it came that way.

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