What is the science behind vacuum sealed bags over just sealed bags?
 
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How do you store your filament most often? Poll is created on Jan 30, 2024

  
  
  
  

What is the science behind vacuum sealed bags over just sealed bags?  

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Rick Lohr
(@rick-lohr)
Trusted Member
What is the science behind vacuum sealed bags over just sealed bags?

I understand that there is less air to hold humidity, but no one seems to worry about that with dry boxes that are oversize.

I'm assuming there is desiccant in whatever method you choose.

Thanks

Rick

This topic was modified 3 months ago by Rick Lohr
Posted : 30/01/2024 2:28 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

You've summed it up, less air less humidity. Halve the air then there is half the water. Yes you need desiccant so what water is in there will go into that rather than the filament.

One other minor advantage of vacuum bags is that it easier to see if you have sealed it properly, if it starts relaxing after you remove the pump, it's not sealed.

If you are thinking of get vacuum bags, make sure you get an electric pump.

Posted : 30/01/2024 2:42 pm
EastMemphis
(@eastmemphis)
Estimable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

I "vacuum" seal my bags by sucking the air out of the bag with my mouth. Not perfect but at least most of the ambient air is removed. I consider this to be "just sealed".

Printables: https://www.printables.com/@EastMemphis_905139/models

Posted : 30/01/2024 2:56 pm
cjameshuff
(@cjameshuff)
Eminent Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

You're technically removing some moisture that would otherwise get absorbed in the filament, but the volume of air in the bag only amounts to a small amount of moisture. It does make it clear the bag is still sealed, and they're easier to stuff in a box or shelf when they're not in big pillowy bags of air.

Posted : 30/01/2024 3:27 pm
EastMemphis
(@eastmemphis)
Estimable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

The absolute best thing to do would be to first vacuum out the air, then refill with a small amount of pure nitrogen. That would help keep outside air from getting into the lower pressure bag.

I just use my mouth as it's the closest vacuum pump at hand and doesn't require any time to setup or use. But I agree with your assessment.

Printables: https://www.printables.com/@EastMemphis_905139/models

Posted : 30/01/2024 3:54 pm
Rick Lohr
(@rick-lohr)
Trusted Member
Topic starter answered:
RE: What is the science behind vacuum sealed bags over just sealed bags?

Thanks for the quick responses.  I was wondering whether the vacuum did anything to draw moisture out of the filament but that has not been mentioned.  I would think that amount of air in the bag would be trivial to humidity control.  I do see value in knowing it is sealed and making it fit into the box easier.

Posted : 30/01/2024 4:12 pm
EastMemphis
(@eastmemphis)
Estimable Member
RE:

In order for the vacuum to draw moisture out of the filament, it has to be a high torre vacuum, and to have a heat source, typically at least 45C. Then you're really cooking. The vacuum in a bag is just less pressure than ambient. It would be difficult to draw a high vacuum in a bag and not collapse the spool.

Printables: https://www.printables.com/@EastMemphis_905139/models

Posted : 30/01/2024 4:17 pm
JP Guitars
(@jp-guitars)
Estimable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

If you got sufficient vacuum then the vapour pressure inside the filament would be higher than that in the surrounding atmosphere so the water would migrate out to equalise the vapour pressures. But in the real world that would be impossible to achieve as the reel would likely collapse and the bag would be unlikely to be able to resist the external pressure.

Posted : 30/01/2024 4:18 pm
cjameshuff
(@cjameshuff)
Eminent Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

The basic idea's physically sound, the numbers just don't work out to it mattering much. If ambient humidity is 50% and you vacuum down 0.2 atm, that's effectively 10% humidity. But 50% relative humidity at 25°C under 1 atm is 11.5 milligrams of water per liter. That's basically a drop of water, and 0.001% of the mass of a full 1 kg spool per liter of trapped air, if every last bit of it was absorbed. Just squeezing out the excess air will give you the vast majority of the benefit, and tossing in some dry dessicant will probably do more than trying to pull a significant vacuum on the bag. (And it'll keep working if the bag gets punctured.)

Posted : 30/01/2024 5:16 pm
Diem
 Diem
(@diem)
Illustrious Member

Cheerio,

Posted : 30/01/2024 6:15 pm
Rick Lohr
(@rick-lohr)
Trusted Member
Topic starter answered:
RE: What is the science behind vacuum sealed bags over just sealed bags?

Thanks for the great responses.  Think I will be getting some vacuum bags, pump and dryer soon.

 

Rick

Posted : 30/01/2024 11:21 pm
Thejiral
(@thejiral)
Noble Member
RE: What is the science behind vacuum sealed bags over just sealed bags?
Posted by: @cjameshuff

The basic idea's physically sound, the numbers just don't work out to it mattering much. If ambient humidity is 50% and you vacuum down 0.2 atm, that's effectively 10% humidity. But 50% relative humidity at 25°C under 1 atm is 11.5 milligrams of water per liter. That's basically a drop of water, and 0.001% of the mass of a full 1 kg spool per liter of trapped air, if every last bit of it was absorbed. Just squeezing out the excess air will give you the vast majority of the benefit, and tossing in some dry dessicant will probably do more than trying to pull a significant vacuum on the bag. (And it'll keep working if the bag gets punctured.)

You are right of course, but the key aspect with vaccuum sealed bags is not so much that there is almost no air left and therefore no moisture in that air but that the vacuum sealed bags are very well sealed. It is the leaks that continuously bring new moisture and consume your dissicant. I could see that very well when comparing IKEA Samla boxes with their airtight sealed 365+ boxes. In the former the silical gel manages to soak up quite a lot of water over one year, in the latter the same silica bag looks almost pristine, even one year later. 

Mk3s MMU2s, Voron 0.1, Voron 2.4

Posted : 31/01/2024 8:16 am
cjameshuff
(@cjameshuff)
Eminent Member
RE: What is the science behind vacuum sealed bags over just sealed bags?
Posted by: @thejiral
Posted by: @cjameshuff

The basic idea's physically sound, the numbers just don't work out to it mattering much. If ambient humidity is 50% and you vacuum down 0.2 atm, that's effectively 10% humidity. But 50% relative humidity at 25°C under 1 atm is 11.5 milligrams of water per liter. That's basically a drop of water, and 0.001% of the mass of a full 1 kg spool per liter of trapped air, if every last bit of it was absorbed. Just squeezing out the excess air will give you the vast majority of the benefit, and tossing in some dry dessicant will probably do more than trying to pull a significant vacuum on the bag. (And it'll keep working if the bag gets punctured.)

You are right of course, but the key aspect with vaccuum sealed bags is not so much that there is almost no air left and therefore no moisture in that air but that the vacuum sealed bags are very well sealed. It is the leaks that continuously bring new moisture and consume your dissicant. I could see that very well when comparing IKEA Samla boxes with their airtight sealed 365+ boxes. In the former the silical gel manages to soak up quite a lot of water over one year, in the latter the same silica bag looks almost pristine, even one year later. 

The point is that there's almost no air left and therefore no moisture even without vacuum sealing. The very example you give demonstrates this...those airtight boxes aren't evacuated. The comparison isn't to completely unsealed storage.

And again, those "very well sealed" vacuum bags can easily become unsealed if the bag gets damaged. You can put silica gel in them to mitigate this, but then you've already gotten basically all the benefit you'd get from vacuum sealing them, as well as a safety net.

Posted : 31/01/2024 2:33 pm
EastMemphis
(@eastmemphis)
Estimable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

Another key point to consider is that even a bag with a leak can be extremely well sealed if it has room to expand and contract with the barometric pressure. What causes a leak to be a problem? It's the "breathing" cycle of changes in atmospheric pressure that causes the gas exchange. A very small leak can defeat the vacuum but even that leak can only exchange so much moisture from diffusion alone, and as long as there's no pressure differential, even a leaky bag will not have a change in moisture level.

So vacuum sealing, while extra groovy and technically better, amounts to more work for very little gain. For me, I just chuck a large bag (40g) of desiccant into a standard gallon (or two gallon depending on the spool) Ziploc bag, suck the air out with my mouth and then put it back on the shelf.

Printables: https://www.printables.com/@EastMemphis_905139/models

Posted : 31/01/2024 2:39 pm
Thejiral
(@thejiral)
Noble Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

 

Posted by: @cjameshuff
 
The point is that there's almost no air left and therefore no moisture even without vacuum sealing. The very example you give demonstrates this...those airtight boxes aren't evacuated. The comparison isn't to completely unsealed storage.

And again, those "very well sealed" vacuum bags can easily become unsealed if the bag gets damaged. You can put silica gel in them to mitigate this, but then you've already gotten basically all the benefit you'd get from vacuum sealing them, as well as a safety net.

Uhm, yes, I am not sure I am getting what you are getting at here. It doesn't really matter if the containment is evacuuated or not because the amount of moisture in the given volume of enlcosed air is negligible. But if your container or bag is not sealed, moisture inside the container/bag can contiously equilibrate with the ouside and thereby there is a slow but continuous resupply of moisture which slowly consumes your dessicant. 

Not sure what you are advocating here. I am actually agreeing that some well sealed containment with some dessicant is good enough for long term storage. Even not so well sealed containment like Samla boxes with dessicant works but there you may have to rejuvinate the dessicant once a year or so.

Mk3s MMU2s, Voron 0.1, Voron 2.4

Posted : 01/02/2024 11:58 am
Zappes
(@zappes)
Reputable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

I'll put it this way: I strongly doubt that vacuum packaging makes any difference with regard to the moisture. But at least it is trivially easy to spot it if your bag has a leak so that you can replace it. 🙂

My models on Printables
Posted : 01/02/2024 4:23 pm
galshemesh
(@galshemesh)
Active Member
RE: What is the science behind vacuum sealed bags over just sealed bags?

I just ordered recently a pack of vacuum sealed bags off Amazon, which also comes with a low powered automatic pump. I really like it, though I do find the Prusament filament bags with the zipper to be of much better quality. Too bad Prusa they add a vacuum pump hole on them so we could re-use their bags to re-seal our filaments inside; would be much better for the environment instead of tossing them away. Hope they will see this comment and consider it.

Posted : 04/03/2024 10:46 am
Zappes liked
Zappes
(@zappes)
Reputable Member
RE: What is the science behind vacuum sealed bags over just sealed bags?
Posted by: @galshemesh

I just ordered recently a pack of vacuum sealed bags off Amazon, which also comes with a low powered automatic pump. I really like it, though I do find the Prusament filament bags with the zipper to be of much better quality. Too bad Prusa they add a vacuum pump hole on them so we could re-use their bags to re-seal our filaments inside; would be much better for the environment instead of tossing them away. Hope they will see this comment and consider it.

That would be really great. They could even sell the filaments either in a resealable plastic bag with the valve or just shrink-wrapped in foil - if you already have the bag, there's no need to buy one again for the refill. Oh, and all filaments should be sold as refills - I'm drowning in empty spools and I hate the plastic waste.

My models on Printables
Posted : 04/03/2024 10:49 am
galshemesh
(@galshemesh)
Active Member
RE:

Exactly. Since I'm quite new I haven't run-out of my Prusament filament just yet, but yes - having empty plastic spools is not economic friendly; would very much like to be able to order only the filament without the plastic spools if I already have empty ones - this should also lower the cost. Prusa could use hard cardboard in the shape of a spool to hold the filament in place during shipping, which you can then move to your plastic spool and toss away the cardboard for recycling.

As for the plastic bags: I really saw their current bags as a total waste since it already has a nice zipper on them which you can re-use to seal other stuff in. So why not add to it a pump valve hole to make it more practicle...? I suppose that if they read this they will surely consider this, as they're making everything in-house and always evolve and improve.

This post was modified 1 month ago by galshemesh
Posted : 04/03/2024 11:24 am
Zappes liked
Rick Lohr
(@rick-lohr)
Trusted Member
Topic starter answered:
RE: What is the science behind vacuum sealed bags over just sealed bags?

I wonder if you could buy just  the pump interface to put on any bag?

Posted : 04/03/2024 1:50 pm
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