unable to dissolve pva in water  

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andrea.m3
(@andrea-m3)
Active Member

Hello, im using Prusa Mk3s with MMU2s installed. I try to print a part (PLA) using soluble support interface (PVA), but when i put the model inside warm water, after 3 hour PVA will be gelatinous and very difficult to remove from the model. Purging volumes is: 140 load / 100 unload for tool#5 where PVA is loaded ... can someone have experience with soluble supports ? thanks in advance

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Posted : 27/02/2020 9:35 pm
cosmith
(@cosmith)
Estimable Member

That's exactly how PVA works.  It never really totally dissolves.  It just gets soft and slimy.

Posted : 05/03/2020 11:51 am
andrea.m3
(@andrea-m3)
Active Member

@cosmith

this is very strange, as you can see from the Prusa video, the support literally dissolve in water .... -->

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Posted : 05/03/2020 1:39 pm
joan.t
(@joantabb)
Veteran Member Moderator

as far as I am aware, BVOH goes gelatinous, but PVA  is supposed to dissolve to solution... 

I have never successfully printed PVA, but samples from trade shows, have dissolved to nothing... 

I wonder what's  going on!

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 05/03/2020 1:58 pm
stuart.b4
(@stuart-b4)
Estimable Member

I suspect agitation in warm water, e.g. an ultrasonic cleaner

Posted : 05/03/2020 2:12 pm
cosmith
(@cosmith)
Estimable Member
Posted by: @andrea-m3

@cosmith

this is very strange, as you can see from the Prusa video, the support literally dissolve in water .... -->

That's BVOH, not PVA.

Posted : 05/03/2020 2:14 pm
vintagepc
(@vintagepc)
Noble Member

Pretty sure it just takes a lot longer than 3h, as tested in the original post.

Posted : 05/03/2020 2:18 pm
stuart.b4
(@stuart-b4)
Estimable Member
Posted by: @vintagepc

Pretty sure it just takes a lot longer than 3h, as tested in the original post.

I've left small prints overnight and still had to deal with slimy mess.

Posted : 05/03/2020 2:28 pm
andrea.m3
(@andrea-m3)
Active Member

@vintagepc

i think so ... i leave 24h and i let you know 😉

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Posted : 05/03/2020 5:04 pm
k7zpj
(@bruce-p4)
Estimable Member

First of all, it isn't as easy and clean as the Youtube videos show.

It helps to remove as much PVA as possible without damaging the part before you put it into the warm water (35C for PLA).

To increase the solubility of the PVA you need to keep the water warm and you need to change out the water every 2 to 3 hours.  I use a small Styrofoam  container to insulate the container with the part / warm water.

It also helps to remove as much soft PVA as you can when you change out the water.

It can take 24 hours or more to remove all the PVA with a part with a lot of supports or dense PVA supports.

Posted : 05/03/2020 5:12 pm
Anachronist
(@anachronist)
Trusted Member

That's right, PVA doesn't actually disappear in water, it becomes gelatinous. I user 3DMaker PVA, and their support desk told me that it can dissolve in an hour in an ultrasonic bath or overnight in still water (8-12 hours), and they recommended removing the gelatin with a brush. They said that the fact that theirs doesn't dissolve quickly makes it easier to print with and store.

First, I remove as much support material as possible before putting it in warm water. For large flat areas the PVA can peel right off. Typically I have crevices and hollow curves in my part. So after half an hour of soaking, I use a small stiff brush or a plastic blade or a toothpick to scrape or peel off the gelatin to expose fresh PVA underneath. Soak in warm water another 20-30 minutes or so and repeat. Be gentle and patient, especially if your part has little crevices full of PVA.

I've printed 3 parts with PVA now and concluded that PLA gets weakened by water. It wants to delaminate, especially if soaked in an ultrasonic bath. Even my trusty Prusament silver-gray PLA, which has had excellent self-adhesion properties, gets really weak to the point where layers can separate easily. This makes it really hard to use PVA with small delicate parts.

Another weird thing I noticed is that PVA leaves a residue on my powder-coat sheet. I have a wet paper towel on top of it now, hoping it will dissolve enough to wipe off. 99% isopropyl alcohol doesn't remove it. PVA sticks better to that sheet than any other material.

This post was modified 2 months ago 4 times by Anachronist
Posted : 09/06/2020 2:16 am
Anachronist
(@anachronist)
Trusted Member
Posted by: @joantabb

I have never successfully printed PVA, but samples from trade shows, have dissolved to nothing... 

It's good to know that those videos showing PVA dissolving quickly and cleanly are actually real. I don't have BVOH, my spool says PVA on it, and my PVA turns into a mass of gel. That trade show stuff that dissolves to nothing, well, I think that a filament being too sensitive to water would make it hard to handle and print.

I wondered if a better solvent than water could be found for PVA. I figured, if PVA means "polyvinyl alcohol" then alcohol might do something, but 99% isopropyl alcohol doesn't affect it at all. Acetone might but acetone also interacts with PLA so that isn't good. I read that methanol is an effective solvent for PVA but at $30/liter it's pretty expensive if you have to throw away the solvent after using it.

Posted : 09/06/2020 5:45 am
vintagepc
(@vintagepc)
Noble Member

Most of those videos are time lapses. don't expect results on the order of minutes. 

From a chem perspective, water (warm) is your best bet. Add something to stir it and get some circulation and it will be even better. 

It's only called an "Alcohol" because it contains hydroxyl groups in the polymer chain. Naming is just naming based on the structure and you shouldn't read into a name to try to determine chemical properties. That's what you have things like MSDS sheets for, those typically tell you solvents, compatibilities and incompatibilities, etc.

PVA is fairly resistant to other common solvents. (Example: Table salt (Sodium chloride) contains chloride in the name but is a far cry from chlorine gas, or the way it behaves in bleach). 

 

Posted : 09/06/2020 2:39 pm
rob.w5
(@rob-w5)
Trusted Member

I tried using soluble supports and found that to this day, I cannot get that smooth PEI sheet clean of that material.  It's gone to the back of the file, designated as "Last choice" in case my other sheets have worse problems.  So I'm not inclined to use soluble supports just for the cleanup required to go on to the next print.
Beyond that, once I have a blob of goo to clean up AND have to pick at it with dental tools/knives, I concluded I'd rather just pick at PVA/PETG with a dental tool/knives.  Messing with the blob turned out to just be additional effort and a lot more clean-up.

Posted : 23/07/2020 6:43 pm
Anachronist
(@anachronist)
Trusted Member
Posted by: @rob-w5

I tried using soluble supports and found that to this day, I cannot get that smooth PEI sheet clean of that material.

In my case, PVA leaves a mark on my powder-coated sheet, but it does peel off completely, and the sheet texture and surface seem undisturbed. The good thing is that adhesion of PLA seems to be better where the PVA had been. PLA adhesion on the powder-coat sheet has always been a problem.

Posted : 24/07/2020 6:51 am
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