Printing PVA = Lots of problems...

[LePaul 321]

Fascinating.  Well @ultiarjan the same symptom is true of the newer formulations of Ultimaker PLA.  If you leave it in the bowden for 8 hours it becomes very brittle!  And it has nothing to do with moisture but has to do with mechanically straightening the filament and holding it in that position for many hours.

That's interesting that you mention that! I have a few spools of new Ultimaker filament in my UMO and on a few occasions, I have had to open the feeder give it a little shove and close the feeder again to get the filament moving.

[Dim3nsioneer 557]

What about UV light exposure? While I don't think that any of you is exposing the filament to sunlight there might be a difference in the light sources you use at the place where your printer stands.

[Psypher246 0]

The statement that PVA gets brittle with moisture is opposite to our experience. Both temperature and moisture make PVA soft.

My experience is the same. Last night my printer jammed completely. See out of focus pic:

Had to take the whole thing apart. After cleaning out the feeder and the printcore I tried again but kept jamming. Increased tension all the way and still jammed. Then I realised how soft the filament felt and realised it must be from moisture, lots of rain and misty days lately.

Will try dry it out on a heating pad as suggested and the dry box seems like a good idea going forward. This is my first time using PVA so did not realise it was going to be this susceptible to moisture but it makes total sense.

[Swissengineer 25]

The statement that PVA gets brittle with moisture is opposite to our experience. Both temperature and moisture make PVA soft.

My experience is the same. Last night my printer jammed completely. See out of focus pic:

Had to take the whole thing apart. After cleaning out the feeder and the printcore I tried again but kept jamming. Increased tension all the way and still jammed. Then I realised how soft the filament felt and realised it must be from moisture, lots of rain and misty days lately.

Will try dry it out on a heating pad as suggested and the dry box seems like a good idea going forward. This is my first time using PVA so did not realise it was going to be this susceptible to moisture but it makes total sense.

Hey,

Yes you have a problem with moisture, here is what you need to do:

Tomhe reply

Then you need to always print what you need, then remove the spool and store in a sealed bag with desiccants inside.

Good luck

[SandervG 1,521]

The statement that PVA gets brittle with moisture is opposite to our experience. Both temperature and moisture make PVA soft.

My experience is the same. Last night my printer jammed completely. See out of focus pic:

Had to take the whole thing apart. After cleaning out the feeder and the printcore I tried again but kept jamming. Increased tension all the way and still jammed. Then I realised how soft the filament felt and realised it must be from moisture, lots of rain and misty days lately.

Will try dry it out on a heating pad as suggested and the dry box seems like a good idea going forward. This is my first time using PVA so did not realise it was going to be this susceptible to moisture but it makes total sense.

Don't forget to bring your tension back to default (the middle) before you start another print!

[geert_2 557]

Fascinating.  Well @ultiarjan the same symptom is true of the newer formulations of Ultimaker PLA.  If you leave it in the bowden for 8 hours it becomes very brittle!  And it has nothing to do with moisture but has to do with mechanically straightening the filament and holding it in that position for many hours.

I really don't know why it does this.  I'm guessing you get micro-fractures occurring slowly over many hours.  Or maybe something down at the chemical bond level?  What REALLY surprises me is that this same thing happens with non-PLA.  I did *not* expect this to happen with PVA.

...

This is a late reply, but may still be useful.

I am pretty sure it are micro-cracks indeed. When you manually bend a piece of translucent or transparant PLA, or when you straighten a bent piece (like a tight-wound piece near the end of a spool), then you clearly see white micro-cracks growing. Some colors show these cracks better than others. If you stop bending the filament and release it, the cracks stop growing. But if you keep it under stress, I guess they will keep growing until the material breaks or almost breaks.

Near the end of spools, I always unwind a few meters of PLA, manually bend it around a skater wheel (7cm diameter) in the opposite direction, and then release it again, so it is sitting very loose on the spool. Then it feeds much easier into the bowden tube and nozzle, and it does no longer cause underextrusion on my UM2 printers (non-plus). But I always see those white micro-cracks indeed.

Most plastics have this, as you see in old plastic parts near areas that have been under stress (typically around screws or clamps), even where sunlight does not come (so the cause is not only UV). ABS, polystyrene and polycarbonate definitely have this. I don't know about PVA, but I wouldn't be surprised if it has this too.

In transparant plastics like polycarbonate you can see the stress by holding a polarising filter before and behind the part. Then you see the typical rainbow colors: the closer these color bands are together, the higher the stress, similar to height lines on a map.

[JPChauvel 1]

So I’ve had my UM3 for a few weeks now and love it but have had a few clogs using the PVA material in the BB 0.4 print core. This became exceptionally annoying when printing something like Gyro the Dodo which takes days. One thing I noticed when the core clogs is that the PVA turns from a more translucent white color to a more opaque yellow and sometimes even brown color, clogging the nozzle and turning the PVA into an almost sandy grit. So I decided to look into the chemical properties of PVA and to my surprise I found that partially hydrolysed (reacted with water from the air) PVA will begin pyrolysis (chemical decomposition from high temperatures) at temperatures above 200 C and the UM3 default setting print temperature for PVA is 215 C. Since it would be a hassle to try to constantly keep the PVA dry even during printing I simply lowered the print temperature and have had pretty good luck with 205 C print temperature. There doesn’t seem to be any indication of under extrusion and the filament flows better and creates cleaner lines. According to the TDS for UM PVA filament it actually has a melting temperature of just 163 C but I think extrusion issues may result from temperatures lower than 195 C especially with higher print speeds. 

 

[gr5 2,167]

It's actually pretty easy to dry PVA since you own a UM3.  Put the spool on the print bed, set the temperature of the bed to 70C, cover it with a towel, and leave it overnight.  Going forward always store the pva spool in a 2 gallon zip lock with some big 45 gram, rechargable dessicant packs.

 

[NBull 14]

If you don't wanna use your printer for the drying. I can recommend a car dehumidifier bag. I have had some really bad rolls, I have saved whit it. I just stopped in a zip lock bag together with the pva rolle and let it sit 3-4 days.

 

 

[geert_2 557]

2 hours ago, NBull said:

If you don't wanna use your printer for the drying. I can recommend a car dehumidifier bag. I have had some really bad rolls, I have saved whit it. I just stopped in a zip lock bag together with the pva rolle and let it sit 3-4 days.

 

 

 

 

Yes, exactly the same as I use; found it in a car accessory shop.   :-)

 

If you want to remove moisture from already bad filament, I think it is best to use both: a big bag of silica gel, in a hot environment (a sealed box on a heated printer bed, or in a computer-controlled oven). The elevated temperature might be necessary to dislodge the moisture from the filament. But be sure to stay below the glass transition temp of the filament, so it does not deform or melt. And then, once dry, store it in a closed box or bag with the silica gel.