Do filament dryers reach the middle?

[Jeff Ratner]

Attached is representative section drawing of a full roll of filament. Since the filament is packed tightly, does putting it in a filament dryer really reach and dry the middle of the spool? Or is this area so tightly packed and shielded that only the outer portions get dried even after many hours in a dryer? Probably worse if the spool doesn't have open slots on the sides.

[Ken Davidson]

Seems to me if it's packed so tightly that the dryer can't get to it, then moisture won't be able to get to it in the first place. The dryer should be able to get to the same areas as the moisture.

Ken

On Mon, Dec 25, 2023 at 7:41 AM Jeff Ratner <jeff117...@gmail.com> wrote:

Attached is representative section drawing of a full roll of filament. Since the filament is packed tightly, does putting it in a filament dryer really reach and dry the middle of the spool? Or is this area so tightly packed and shielded that only the outer portions get dried even after many hours in a dryer? Probably worse if the spool doesn't have open slots on the sides.

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[Jeff Ratner]

If you've ever seen how filament is made - it gets extruded then runs through a long rectangular tank of water to cool. It should then be fully dried at the factory but it might still have a little moisture from this cooling process, possibly wound into and trapped in the middle when you receive it. I used to think people were crazy for drying new rolls of filament but after seeing how filament was made, I can see how it might help. Just not sure if the dryer can reach the middle. 

[Dan Flemming]

As a precaution to exactly that, I dry as I print.

I have a dryer on all my printers.

For instance,

  My new tpu prints with less stringing that without drying while printing.

I have many rolls of 1/4 or less spools that I occasionally use, I start drying about 2 hour before use and continue until I stop printing that spool.

Just insures the older filament is a bit more pliable, and less likely to cause problems.

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[Dan Flemming]

Typo correction:

I start drying about 2 hour before 

Changed to

I start drying about 1/2 to 1 hour before 

[3D Printing Tips and Tricks]

My cohost and I both live North of the Golden Gate. It’s considered semi-arid. I grew up back East and I remember well what real humidity feels like so our experience on this subject could be completely wrong for those who live where the Cicadas sing. But in our experience moisture is not as big an issue as so many make it out to be. We see the effect of moisture in two ways, first in how evenly the melting is across the spool. If moisture in the filament is high flow rate is effected. The materials’ glass point varies up and down.  We can usually hear it with hissing and popping at the hot end and see it in the unevenness in extrusions. Second,  the outer diameter of the filament expands and can go out of tolerance. We rarely see these issues here. On the other hand… PLA goes brittle real fast and our experiments have shown that this is due to UV  light exposure. It depends on the pla formulation. Some are worse than others.

My point is, do not assume per posts online that moisture in your filament is as big a deal to you as it is to others..

[Jeff Ratner]

I live in the humidity armpit of the US (Florida). It's not bad here this time of year but in the summer humidity is super high. I do agree with you that moist filament might not always be the cause of various issues it gets blamed for. I've got some partial rolls of PLA that have been sitting out in the open (in an air conditioned house) for 5 years that still print fine. And I've had some brand new vacuum packed rolls of PLA that were super brittle right out of the vacuum sealed bag, and remained brittle even after many hours of drying. 

[3D Printing Tips and Tricks]

There ya go… per our tests drying and moisture are not why pla goes brittle. Yet over and over again I see posts where folks just assume they are related. Vacuum packed rolls in clear plastic will still allow UV light through.

[Alan B]

Is this PLA UV embrittlement process a proven fact or just a theory? 

My filament is generally stored in 5 gallon buckets with gamma seals and eva dry dessicant packs. The only window is north facing and the curtains are always drawn. There is very little if any UV in the room. The PLA gets brittle, even when stored in the factory boxes and packaging. It seems to get brittle with age. It does seem to be worse when it sits on the printer, but there is no UV, only moisture at about 30-40% humidity in the room. Within a few days it will break at the printhead. So moisture seems to exacerbate it. I have little doubt that UV will cause embrittlement, but many situations are absent UV so that isn't the cause there.

I respooled some really old filament. It seemed fine. Then a few days later the spool was all broken segments. There was no UV, especially on the inner coils of a black spool. The whole spool was broken up. As I recall that was stored in a gamma seal with dessicant after removal from the factory box.

I think the PLA breaking is not properly understood and apparently has multiple causes. It doesn't seem to happen once an object is printed.

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[3D Printing Tips and Tricks]

As I’ve posted before, for the podcast we took 3 coils. Put one in a pail of water, one out in the sun one in a dark closet. One day. Maybe I can repeat that segment or simply do it again.

The one in the sun was brittle.  The other two were fine.

For sure there are other factors but I’m convinced enough to always remove pla spools after printing and storing them in the dark.

[tray]

If you do decide to rerun your experiment, it'd be fun/illuminating (pun intended) to expand it slightly. Sunlight is a lot more than UV.
Ordinary window glass mostly blocks UV below 350 nm (UV-C, UV-B, and half of UV-A) - maybe put a coil under that.

Also maybe under a piece of UV-blocking glass or plastic to see if just really strong light (or the thermal cycle it creates) also has an effect. Even a piece under really bright LED lighting might be interesting.

No question UV is bad for PLA - just check out researchgate for papers on that topic. I haven't read up to know if particular bands of UV are the culprit. Just sorta assuming none of them are good for it.

I agree Alan that solar UV doesn't sound prominent in your situation. Cheap fluorescent or LED lighting can also put out some UV, since both commonly start with a UV source and convert to visible, and some of that UV can escape. So UV affecting things is still possible.

>Within a few days it will break at the printhead. ...  It doesn't seem to happen once an object is printed.

Juxtaposing those statements brings up a few points. Filament going into your printer is being bent and twisted, while your printed object is (usually) not. Also melting it for printing resets the degree of crystallization and the composition changes a bit from reaction with moisture and oxygen. 

[Alan B]

No fluorescent lighting, one LED bulb indirect reflecting from the white ceiling for room light. Window is north facing with sheer curtain, sunlight doesn't directly come in there. There just isn't much UV in this area. Curtains are old and not degrading.

PLA breaks where it straightens out, on the spool inches away it is fine. Generally takes about 3 days of sitting to do so.

Same behavior has been noted at two other locations in the house with different lighting conditions. Humidity around 30-40% in the house.

No doubt UV is hard on PLA. But it is not the only thing that is going on, apparently. Moisture also causes chemical reactions in the filament and some are not reversible by drying. I wonder if visible light is also a factor. Very little if any UV from white LEDs, their main output is in the blue range. UV LEDs are very special and quite weak.

The worst filament I had was 2 rolls that sat in the box from 2014 to 2017, away from UV. It worked for awhile then started breaking up after respooling. and then the whole spool snapped into lengths. Not much UV or any light inside the spool. But moisture was likely an issue.

After listening to several hours of the podcast on PLA by Pooch and the Gloop materials scientist the consensus that I remember was that PLA has a limited life before moisture induced chemical changes make it brittle and drying does not reverse all of these reactions. So the best course of action is to keep it in dry conditions and don't leave it on the printer. Repeated drying of PLA is not good. Use it up, don't let it get too old. Drying PLA doesn't revert it to as new.

Note that other filament types are not the same. Each polymer has its own characteristics and reactions to humidity and other environmental conditions. So you cannot generalize the behavior. But storing them with desiccant and keeping them out of UV and away from light in general is a good start. Much of my storage is dark - gamma sealed 5 gallon buckets with Eva Dry desiccant modules. But some of it is also transparent like PrintDry or Sterilite plastic containers, still with desiccant. So far I haven't noticed a difference between dark and transparent storage but the conditions are not well controlled with reels moving between the conditions. The ends of filament occasionally break in storage but not in the spool. So in all cases the broken filament was subject to stress and then took some time before it broke. So moisture, stress and time appear to be key factors.

Regards, Alan

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