"And if I put the lid back down, you can see that the relative humidity almost instantly
rises again.
Oh hi. This episode I'm going to be proving that PLA gets wet, along with sharing quite
a few other observations I found on the way. This is a good one, so take a seat and grab
some popcorn! Let's get started.
The filament dryer in this episode has been provided free of charge by Sovol. The terms
of the exchange in exchange for showing it in the video are on screen, so thank you sovol
for providing this and enabling me to do a lot of what's in this video.
I wasn't going to touch the idea of wet filament with a barge pole, in fact, I've actually
done this before, well I've actually done videos about moisture before but very few
people watch them, which is fine. I guess.
Anyway to get to the point, here's some background. I did not believe that PLA filament can get
wet. Why? Well, I've never suffered from any moisture
related issues, so of course it didn't make sense for PLA to be able to absorb water from
my environment. Maybe in some far away lands where there's weird looking birds it might
be a problem but no, not here in sunny dry england.
But then I started messing around with this dryer. You might be wondering, why on earth
are you reviewing a dryer if you don't believe in wet filament, well short answer is that
I do believe that moisture affects filaments like this PVA here, so I needed a way to dry
this.
Anyway, the problem is, well, watch. I put this reel of PLA that's been open a while
into the dryer, while the dryer is hot, and close it, and the air inside gets...wait for
it...
...more moist!
To understand what's going on, we need to step back a bit and look at the theory. I've
been advised by at least three separate people that I absolutely shouldn't open this can
of worms but you know how it is, I don't listen. I'll plough through this quickly so you don't
notice the mistakes.
Relative humidity is a percentage value representing a proportion of the amount of humidity the
air can hold. This changes with temperature, and pressure, but we'll ignore the second
one because it's convenient to do so. Hotter air can hold a LOT more moisture, here's a
graph that proves it. I didn't draw this. It's from an important science..book.
But that means that a volume of air that's sealed inside a container, when heated up,
if you're measuring the relative humidity, that reading will go DOWN. Why? Well pay attention,
I literally just explained that. But the amount of water in that container in grams per meter
cubed doesn't change at all.
Now this sovol dry box is different to every other dry box I've seen because they've put
a gasket around the lid and there's even airtight thingies on the top and back. What this means
is that I can do exactly that experiment and plot a graph. Here it is. And luckily the
relative humidity does indeed go down as the air heats up. If I bothered to leave this
to cool down it would be the other way round and I'd be able to see how airtight it is
but I'm on a deadline so let's not.
But because it's a sealed container, well, as you saw at the beginning, I can put a reel
of filament in, and if it's already up to temperature, I can nearly instantly tell you
if there's moisture in the reel or not. You can do this over and over, put filament in,
close it, watch values go up, open it, watch them go down. The moisture isn't appearing
from another dimension, it's from the filament, or I guess initially from your hand but let's
ignore that because we have more tests!
What I did before with heating up the empty box and making a graph is now useful, because
I can do the same thing with a reel of wet filament and see the difference.
There's a huge difference, but can you see it?
It's important to note that I was doing these experiments during a relative heat wave in
the UK which was totally messing with my initial conditions, so ignore the start temperature
and the gaps in the chart. Humidity varies a LOT throughout the day as I discovered,
so it's nearly impossible to start with the same values, but that's not what I was looking
for. What I was looking for, was new moisture appearing while I heated up the chamber.
If you do this with used silica gel, it's pretty obvious, you get actual condensation.
Silica gel is insanely good at adsorbing, yes with a d, let's not go into that, so much
so that it literally lets out steam when you heat it back up. And yes by the way storing
silica gel in a box with wet filament does dry it - I don't want to make the video 10
minutes long so you'll have to take my word for it.
But moving on, I thought I'd do some measurements of temperature vs humidity for a few reels
of filament and I found some surprising things, to me at least, being a moisture denier. If
I show you the full graph for all the filaments I tested before I literally ran out of open
reels, they nearly all have this tiny flick up at the end, and you can see some diverge
when they get over 40C.
To be clear as to what you're looking at here, the relative humidity at some point when the
air around the filament heats up, the relative humidity goes UP. There's no way this is possible
for a closed box of air which is why thankfully we didn't see that with the baseline, it would
have taken some serious explaining, but with every single reel of filament, it happened
and to my mind it means exactly one thing - they're all expelling moisture into the
air. I even saw some signs of the brand new filament REMOVING moisture from the air when
cold, but then adding it while warm, which was quite amusing but when you think about
it, it's exactly what the silica gel would do so it's pretty much an expected behaviour.
Anyway I want to address a couple of things. Firstly, this is not a good way to dry filament.
As I showed you earlier, you can open and close the door and keep repeating the process,
this is because you're in a closed system, you need convection to remove the air and
give you some more air, so that you can continue to remove more moisture. The dryer actually
has a fan in the back which is really cool, and if you check the manual you will see more
evidence that they know what they're talking about because they actually tell you to prop
the lid open when drying. If you have a filament dryer that mostly seals and you're not doing
this then you're really just warming up your filament.
Once your filament is dry, seal the box and it keeps dry. Very clever. You can even put
some dessicant in to deal with any tiny leaks.
Second thing I wanted to address was raised by one of my patreon patrons and they are
absolutely right. The diagnostic process of sealing filament in a warm sealed space and
monitoring the humidity does not tell you how much moisture it has. To do that you would
need to use more sophisticated methods. I didn't really look into whether the equilibrium
point is any vague indicator of how much moisture there is although if you look at the graph
for the PVA you can see it's obviously more hygroscopic but this was beyond the scope
of the video, maybe for the future.
Something else I didn't really look into was the effect of drying on printing. Well, A
really good example of this can be found on filamentstories' channel which I've put a
link to in the description, it's a really good channel, go check it out. I did do a
brief test also with one very old reel of PLA and was able to reproduce a definite difference.
So what is the take away here then? What's to learn? Well, firstly I've totally changed
my stance on storing and drying filament. Previously I would have told you to protect
from dust but ignore moisture, with PLA at least. Now I would advise you to store in
sealed bags with dessicant.
Secondly, I think it's worth considering that nothing is really dry or wet, as we've seen
from the evidence. I feel like you can always get more moisture out of a reel of filament,
and I also feel like there will be an acceptable level of moisture in the filament, in fact
Joel from 3d printing nerd implied as much in a tweet response to me when I mentioned
this, and I am inclined to believe this fact presented too, the idea that a filament has
to be fully seems arbitrary, but the thing I think is important is that it's a scale,
not a binary value.
And finally, I think there is merit in owning a dry box or a way to dry filament, I polled
you all, and the bulk of you either had or were interested in a dry box, I might do another
poll and see if these values change, that would be fun, but I do think drying filament
before printing or before putting it away is worth considering.
Of course you absolutely don't have to buy a dry box like the sovol one that I have here,
you can achieve the same with any heated volume, in fact you can dry filament on your printer
bed if you want, and while I think it's worth the money because of the seal and the humidity
display it's essentially up to you how you do it.
Of course, in making this video I had to ignore or simplify a LOT of the complicated stuff
to do with this topic, I do know I've done that, for better or worse, but hopefully it
has been of some use. Let me know in the comments whether any of this has changed your mind
on how to store filament or if you think I'm right or wrong. Also did you think this was
more interesting than a basic dry box review, because that's something I'd like to know.
As usual links or corrections below in the description. I've got a couple of REALLY good
videos coming up which I'm keeping a tighter lid on than this dry box has...sorry...so
make sure you are subscribed, I will see you next time!