4 hours ago, kmanstudios said:
This is definitely not a humidity issue as humidity would make it softer and not brittle.
In my experience this is not the case.
My filaments, especially PVA, have often become brittle, and drying them out in the oven for 6-8 hours has restored them in all cases.
I've dried out my spool of PVA 3 times now and its still printing flawlessly.
That does not seem to make sense to me as if getting moist made it brittle, it would do so when dissolving it. PVA by nature is going to soften and dissolve when moist or wet.
Why would it get brittle?
I'm having the same issue and at the same time hearing "pops" when it is printing, so was leaning toward it being a water saturation issue. Yes, I know it doesn't make sense that it is more brittle, but the sound it makes when printing seems typical of moist PVA. My spool of PVA is older (3-4 months), always kept sealed in a plastic bag with desiccant, in a plastic storage box with desiccant, and only the last few meters of the spool has this brittle issue.
Last print I just let the broken bits stay in the bowden tube and pushed it through with more off the same spool. Sure, I didn't get retraction, but it worked well enough for what I was printing............
8 hours ago, kmanstudios said:That does not seem to make sense to me as if getting moist made it brittle, it would do so when dissolving it. PVA by nature is going to soften and dissolve when moist or wet.
Why would it get brittle?
I've had PVA get brittle when left exposed in a heated office over a winter where we were running the heat a lot. The PVA got brittle (over the course of about 6 months sitting exposed), and it broke into multiple pieces in the tube.
So essentially if you dry it too much...it gets brittle instead of flexible like it does when humidity gets into it.
Our current humidity here has been ranging from 70%-90% over the last few weeks. My printer is in an unheated room (as are all my spools). I cannot see how the PVA would be too dry so as to become brittle.....
It's a mystery to me why it would so brittle as to fracture (it has done so several times over the last few meters of material), yet still "pop" when melting in the nozzle.
17 hours ago, kmanstudios said:That does not seem to make sense to me as if getting moist made it brittle, it would do so when dissolving it. PVA by nature is going to soften and dissolve when moist or wet.
Why would it get brittle?
Yeah i was skeptical at first aswell.
But sticking it in the oven reverses the issue for me every time!
I wonder if this is something similar to what happens when people put brittle PLA in the oven and it gets more pliable.
I am just thinking it is not a humidity related issue, but some other process. Heat does more than just dry things out.
Would be nice if someone with some sort of chemistry experience would chime in so we were not just all guessing.
@SandervG, is there someone at UM that can explain this behaviour?
At least some kinds of PLA i've had consistently get brittle with age, whether on the spool on in printed form. Lots of people kind of deny it, so I'm not sure if they haven't had printed PLA things aged a good amount of time, or if it is formulation issue, or environmental, but for sure some of it does. Also, if I leave a roll of PLA on my machine for a while, it will almost surely break where it is stressed in a week or two (this is on my other non-UM machine, 1.75mm).
I've had PVA break at the extruder many many times when first loading. Sometimes I just cut off the first meter now if I haven't used it in a while. I think one issue with that is when the UM unloads the PVA, the 'cold-ish-pull" it tends to do can grind a dent into the PVA -- I've observed it. That becomes a weak point. The new firmware tends to lessen that as the filament tends to pull a lot easier on unload. Just my experience.
Edited by PaulKJust used my oven to dry the brittle PVA that was fracturing earlier. Right out of the oven and warm it was much more pliable. Printed with it and heard less "popping" sounds and it did not fracture when feeding it.
On 3/16/2019 at 11:54 AM, kmanstudios said:I wonder if this is something similar to what happens when people put brittle PLA in the oven and it gets more pliable.
I am just thinking it is not a humidity related issue, but some other process. Heat does more than just dry things out.
Would be nice if someone with some sort of chemistry experience would chime in so we were not just all guessing.
I have read that PLA gets harder and more brittle due to changes in crystal structure. Over time it changes from rather amorphe to rather crystaline. This makes it harder but more brittle. Placing it in an oven for some time, could sometimes revert the crystal structure back to amorphe, to some degree. However, it could also have the opposite effect, speeding up the crystallisation...
The same mechanism is said to be at work in plastics that you need to put in boiling water, after which you can mould them by hand for some time. When cooling, they stay mouldable for quite long, before the crystal structure changes back to crystalline and they get hard again. Often the color changes from clear to opaque white too. So you need to put it in cold water to solidify it faster. That is how the manual explained it.
Then there is hydrolysis, where water-absorption breaks molecules. I think this is a bit similar to UV-light breaking molecules down and making plastics brittle? (Although I am not sure how this would apply to PVA, since this is basically glue? Or maybe it is a reversible process?)
I am not a chemist; so this is just what I read on the internet and in manuals. Anyway, in my experience, 3D-printed PLA snap-fit lockings that worked very well when freshly printed, do break when using them after a year: they have become too hard and too brittle, and they don't bend anymore.
In addition, I found that in PLA-filament under continuous stress, micro-cracks do develop. This happens for example when you straighten a tightly wound piece of filament, and you keep it straightened (fixed) by clamps. Under a microscope these cracks are clearly visible.
So I would not be surprised if some of these mechanisms could also be at work in PVA? But which ones, and in which proportions? I would welcome the views of plastic-engineers from big plastic manufacturers (Bayer, BASF, DuPont, Eastman,...) on this.
Photo: micro-cracks growing in stretched PLA filament. This is colorFabb natural 2.85mm, but I have also seen it in other PLA-filaments. Photo taken through a microscope. Maybe this also happens in PVA? Try cutting off a piece, stretch it under a microscope, and see if you can see any cracks growing? Then try again at different temperatures and moisture-levels?
On 3/15/2019 at 2:04 AM, kmanstudios said:you just may be in the really unusual situation where the PVA is so dry, it cannot relax enough to straighten out enough to feed properly.
I have 3 different rolls of PVA that have been kept in their dry-bags with silica, but I keep having this problem. I knew that PVA would absorb the moisture in the air (which is why they are kept in bags) but I didn't know they could get too dry. (I had the assumption that maybe they were too dry and needed a little moisture, but thought it was a long shot...maybe not)
On 3/15/2019 at 6:34 AM, ScanHD said:My filaments, especially PVA, have often become brittle, and drying them out in the oven for 6-8 hours has restored them in all cases.
I've seen different posts that say you can "bake" PVA to dry it out. Now I'm seeing that this may help it to not break in the feeder. Do you have a temp that you used, I might do a few experiments.
Just be careful putting them in the oven as an oven a low temps can fluctuate too much and overheat the spool. I tend to use the heat bed of the printer.
A food dehydrator also works very well.
If it is too dry then I would leave it out in open for a 4 or 5 hours and it would soften enough. But I live in 60+ humidity
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2 hours ago, Labern said:I tend to use the heat bed of the printer
So just place the spool of PVA on the bed and turn the heat on. I'll try that too (but might also try the oven on a length or two to see if that works, got any temps and times to try?
I left it out just not that long. I think I'll do a test with a short piece left out over night
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This is definitely not a humidity issue as humidity would make it softer and not brittle. When you get to an end of a roll, the winding is much tighter and you just may be in the really unusual situation where the PVA is so dry, it cannot relax enough to straighten out enough to feed properly.
This happens on many other filaments as well. But, most are not hygroscopic. As counter intuitive as it may sound, you may need a humidifier in your room to get to around 50% or, just slightly less to let the PVA soften a bit to unwind.
For other filaments, I use those ends as a cleaning filament. PVA may (probably) would not be good for that. But, you can recycle it into water to make a slurry for bed adhesion.
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