Drying filament ?  

Re: Drying filament ?

this is an old thread but i have a relevant question:
is there any reason i shouldnt just set my extra PLA filament in a fridge when i'm not using it? i cant really find any recommended storage temperatures, and given that cold dry air helps dry things... is there something i'm missing that would make this a terrible idea?
presumably if you let it warm up in a dry area/box it wont even collect much moisture via condensation.
i've literally gone over everywhere i can find and nobody mentions refrigeration as a do OR a dont so i need to ask XD
i even see studies of pla stability at various temperatures, but nobody seems to check anything lower than 30C

Re: Drying filament ?

Don't know about the filament, but I would be worried about the food that the filament displaces. I have a lot of spools of filament. And I love to eat. 😀

Re: Drying filament ?

Even though it's an older thread, I think there is still a lot of good information in here about filament drying. I just finished reading the whole thread from the beginning, as I was looking for some information on how to dry out a new roll of filament that seemed to be having moisture-related print issues. It could just be a bad spool, too.

For the record, I store my filament in 12" x 12" x 6mil clear bags from McMaster-Carr (Item 19215T16, USD $13.40 + shipping for 25 bags), using the dessicant pouches that came with the filament. I keep the bagged filament in large IKEA Samla boxes. I have only been 3D printing for about four months now, but I should probably replace or dry out some of my dessicant packs.

Kayla makes a very interesting point about drying filament in a refrigerator (or for that matter a freezer). Aaron also has a point that this not a long-term filament storage solution for people who eat, but it might be useful as a DIY approach to filament drying when you have one or two problem spools (if it works, that is). 💡 I am going to try leaving my problem spool in the freezer overnight and see how it does.

Re: Drying filament ?

Alex, wouldn't the water turn into crystals if cooled to freezing point? I'm not sure how a homogenized hygroscopic material that has saturated behaves when frozen but I think it is a good guess that crystals would form rather than leave the material. Since water expands 10% volume when frozen, wouldn't it chatter the amorphous polymeric structure of the plastic reducing strength? Maybe the hot end's melting would rejuvenate the polymer strands but then you have the voids left by crystal assuming the water left at all.

Best case, you have micro-bubbles in your filament extruded and now in your part, better than moist print. Worst case, you made a larger jagged hole for the water to convert to steam allowing easier exit of filament in hot-end. Again likely still better than explosive bubbles as in direct moist printing but still not optimal considering your dehydration efforts?

I believe there is no free lunch. Slow heating in a dry oven is best so you never have shock steam caused by direct energy such as microwave, which I also think is a bad idea. The moisture never leaves as steam but as evaporation which it is presumed will compression close any structural voids where moisture might have pooled, again I'm not completely sure about homogenized blah blah. Works for the pros with fancy pressure kilns, we can do it at home but it will take longer.

Re: Drying filament ?

@Kayla: I wonder why you assume cold temperatures helps keeping things dry?

Decreasing temperature increases relative humidity (up to condensation if the dew point is reached), see
https://en.wikipedia.org/wiki/Psychrometrics
I am still not 100% sure about the physics behind drying, but this reference
https://www.ptonline.com/knowledgecenter/Plastics-Drying/Resin-Types/Hygroscopic-VS-Non-Hygroscopic-Resins
explains that humidity transfer (getting damp and drying) is simply a matter of vapor pressure equilibrium. I wonder if this is true or if the increased temperature has another function (besides lowering relative humidity), like "mobilizing" water molecules in the polymer.

Anyway, this is how I keep my filament dry: https://shop.prusa3d.com/forum/print-tips-slic3r-settings-kisslicer-model-repair--f12/dry-storage-box--t6223.html
I realized that I made a mistake in relying on the humidity measurement. As filament is hygroscopic, putting it in a water vapor pressure tight box will result in a drop of relative humidity - but not indicating a drying progress, but quite the contrary... So if you put silica gel inside the storage container, it is essential to monitor the state of the silica gel. That's what the color is for - mine is orange when active and blue when saturated. I guess silica gel bags are not helpful as you probably have no indication of their health.

- Martin