Does anyone have deeper knowledge in what % RH you need to store say Nylon filaments at to keep them from absorbing moisture?
Zero will work.
@mark_warlick Zero is a pretty unrealistic level unless we start doing dry nitrogen purging / vacuum drying with equipment way more expensive than most people’s printers… I am more after a level that is “good enough”.
I have so far only used untreated Nylon, which absorbs water like crazy (of course, Taulman is much better). I usually keep it in a container with a pound of desiccant, but I am also living in a foggy city. If the desiccant is fresh and the container somewhat sealed, the electronic hygrometer I’ve put in the container is showing an error reading, so it is too low for it to measure.
Since I am printing this Nylon rarely, usually the leaky container makes the RH rise to 20% again or so; then the Nylon works a lot better when I put it through a drying-cylce with a fruit-dryer before use:
https://plus.google.com/u/0/+HennerZeller/posts/7NfCLHyZKSd
@Erik_Cederberg
A vacuum pump and some seal a meal bags should be sufficient to your needs.
I also have a fruit dryer and believe that a day or two of max heat makes a difference. I found a three year old spool of ABS, which may not absorb much moisture, but after three days in the heater, seemed to work far better than I expected.
I haven’t printed anything with nylon yet, although I have a full spool. I opened it to pull some out for nylon nozzle cleaning, then used a FoodSaver™ vacuum bagger to close the remainder of the spool, including a dessicant bag.
The nylon that I use for nozzle cleaning turns into carbonated nylon as it exits the nozzle. The tip of the nozzle could be used for feeding a sauna, there’s so much steam coming from it, but I don’t protect the short length as there’s no real need to do so.
The food dehydrator does wonders for dessicant, both bag and loose form. Some of my loose stuff had turned nearly clear. After a couple hours in the food heater, it was so dark, I was taken aback for a moment.
I’ve learned of a product called Bloxygen (http://www.rockler.com/bloxygen-gas-for-preserving-unused-finishing-materials) which is argon in an aerosol (incorrect term) can, used ostensibly for removing oxygen and moisture from cans of paints and adhesives and other products. Argon is heavier than air by 39% and is drier than air. I’ve not done research regarding the humidity factor, however. One would hope that the air that is displaced by the argon gas also takes the suspended moisture with it.
I see now that this stuff may be the answer I desire for Gorilla Glue becoming impossible to use shortly after opening.
In terms of 3D printing, I’m hoping to have time to make some experiments with a gasketed bin organizer. One filled with argon gas (80 cu. ft. welding tank) and one filled with ordinary air. Dessicant beads in the bottom of each for a week or a month, to see if one is drier than the other.
Paying US$12 for a tiny can isn’t cost effective for protecting bins of filament, but an 80 cu. ft. tank can fill many for far less money.
http://www.rockler.com/bloxygen-gas-for-preserving-unused-finishing-materials
@Henner_Zeller Interesting, so 20% is obviously humid enough for the Nylon to experience printing problems, so we need a storage with 10% or less humidity?
@Erik_Cederberg it’s an equilibrium thing. The more humid the air, the more moisture will be in the nylon. Industrial plastic extrusion guidelines say you want as close to zero moisture in the nylon as you can get, or less than 0.2%. That requires very, very dry air to maintain. I can’t find an equilibrium curve but I’m thinking less than 10% RH will be required for that since equilibrium for nylon in regular indoor air of 30-65% RH is 1.5-2% water content.
My moisture sensors only go down to 16% so I can’t tell you exactly what the RH is for my nylon drybox, but I find that silica desiccant is not aggressive enough, and the nylon will actually pull moisture out of the silica. Any moisture that gets into the drybox will go to the nylon, not the silica. I use calcium chloride (damp-rid) in a polypropylene tub after putting the filament through an oven drying cycle and that works really well. Polypropylene has very low permeability to moisture – much better than a vacuum saver type bag or ziplock. And the calcium chloride grabs water more aggressively than the nylon does.
I found this table in a paper from BASF: http://www8.basf.us//PLASTICSWEB/displayanyfile?id=0901a5e180004880
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I looked at a Psychrometic Chart to get the moisture content for air @ 23C and 1 ATM.
30% = 0.005 kg/kg
50% = 0.0095 kg/kg
62% = 0.0115 kg/kg
100% = 0.0175 kg/kg
10% would be 0.0015kg/kg @ 23C
According to this site, you need to get the dew point of the 80C air used for drying down to ~0C to get the moisture content in the Nylon down under ~0.2%
If i read the Psychrometic chart right, you would need to have less than 0.0035 kg/kg water to bring the dew point down to 0C
This would also mean that the RH of the 80C air used for drying need to be really really low… 80C air with a dew point of 0C is About 1.3% RH according to this calculator: http://www.sugartech.co.za/psychro/index.php
The 16C dew point they show gets the nylon down to 0.25%, that is closer to 4% RH.
This is all at 80C tough, the question is if it is the same equilibrium by weight at room temperature, because then it would be OK with a 22% RH at 23 C, or if we need to go by the RH and down to <5% RH for dry storage.
http://www.toray.jp/plastics/en/amilan/technical/tec_007.html
Looking at this chart from https://www.sorbentsystems.com/desiccants_charts.html, it is easy to see why the silica gel does not work well, it looses almost all of its h2o capacity when going to low humidity levels, while CaO performs well down to just under 10% humidity.
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But we can also see why Silica gel is so widely used, it is way faster at removing the initial amounts of moisture:
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I found a euilibrium chart, even if it is a bit low-res it gives a idea. This means that you have to store Nylons at somewhere between 5% and 10% depending on the type to keep the moisture content to 0.2%
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