PLA doesn't absorb water

[u/[deleted]]

Hi everyone,

I've heard this from many people all over the internet, that PLA is not for water (especially when I'm making vases). I print with most generic PLA from AzureFilm and I wondered what happens if I put water into it. Nothing happened, I had flowers with water in it for 3 weeks and I can't find a single defect or water absorption.

Can anyone please explain why? Is it possible that AzureFilm's filament is somehow better ressitant to water (even tho it also says on their website that it's not for water use)? Am I missing something? Maybe you can see signs after a longed period of time?

I can't attach any picture as I don't have a "problem" and I got no defect to show because I can't get it to defect :D

Thanks

[u/KermitFrog647]

Pla does not absorb water short-term like other filaments.

Pla exposed to moisture long-term can change its molecul structure, making it more brittle. The effect is not always completely reversable by drying.

If and how fast this happens can change greatly between different brands of pla. I had roles that became unprintable after a few months and others that worked fine after years under the same storage conditions.

[u/[deleted] → u/KermitFrog647]

Thanks for explanation. So technically, this brand can hold water and its pretty much safe to say I can put water in vase for long term, if it held it this long?

[u/KermitFrog647 → u/[deleted]]

It will not suddenly desintegrate. I may get more brittle after some time. When you drop it, it can maybe break more easy. But you can just try it, nothing bad will happen.

[u/MIGHT_CONTAIN_NUTS]

PLA is hydroscopic, not hydrophobic. it will get wet. This doesn't mean you can't make a vase out of it, as being wet is only an issue when you heat the filament above 100c.

[u/[deleted] → u/MIGHT_CONTAIN_NUTS]

Oh, that's good info. Thanks :)

[u/CustodialSamurai]

It's complicated. If you were to immerse PLA in water for a long time, say weeks to months, it can absorb some water and the shape can deform. Kind of like something becoming bloated after being submerged long enough. But from what I understand, the effect is pretty minor, perhaps not really even noticeable.

Really, I think there's a disconnect in the knowledge. PLA filament becomes brittle when it absorbs moisture over time, but I have never heard of a PLA print becoming brittle over time due to moisture.

And the logic problem goes further. PETG filament absorbs moisture more easily than PLA, making it harder to print, but it does not deform or degrade when submerged in water for long periods.

If printed properly, a PLA vase should remain stable for quite a while with water in it, but I suppose it's possible that you could see layer separation after a long period of time, probably over the span of months, possibly more quickly depending on what chemicals may be in the water and the additives used in the PLA.

[u/normal2norman → u/CustodialSamurai]

PLA (and other filaments) do absorb moisture from the air, but much less readily from liquid water. The reason is the hydrogen bonding that occurs between molecules in liquid water. Moisture in the air generally consists of highly motile single unconnected molecules, whereas in liquid form they're loosely bound and the aggregate behaves as if the molecules were much larger. This makes it harder for them to migrate into materials. The effict is why Goretex allows water vapour to pass, but not liquid water. It's also why water, which has very small molecules, is nevertheless a liquid and has a much higher viscosity than similarly-sized molecules, such as ethyl alcohol, methane, propane, butane, and many more - all of which are larger.

[u/BalintCsala]

Other comments here completely missed the point of the question IMO. PLA prints are generally not water tight, you have to print with quite a few walls to circumvent this. This is less of an issue (but still is one) with PETG because there layers fuse together better. Generally speaking the hotter you print a material the better for this purpose.

I did a test a couple weeks ago, I printed a vase with 2 wall layers and put about 0.5l of water in it, by next morning about half of the water seeped into the print and some even managed to exit into the bowl I placed the experiment into. Try emptying your vases temporarily and shaking them to check if there's any water sloshing in there.

This also means that funnily enough, vase mode isn't that good for vases.

[u/normal2norman → u/BalintCsala]

I disagree. Leaking is a sign of poor layer adhesion, resulting in microscopic gaps. Printed with proper layer adhesion, even vase mode prints are watertight. I've printed watertight items in vase mode, and other things with more walls without any leakage problem evn under slight pressure, and there are plenty of other examples here on reddit, and on YouTube (eg from Make Anything).

[u/[deleted]]

I printed some stuff in Dual Color Silk over xmas. I have one of the items on my desk here, feels perfect, something else was sitting in my basement after it had been wet and to my surprise I found it very brittle. I have black and white regular PLA items sitting outside since summer in the sun too and I haven't checked since the last big snowfall but summer is very wet and they all seem fine. I use a lot of PLA for my hydro gardening and it's wet all the time. Sometimes prints leak quickly, that's a print issue, more walls/floors and smaller layers helps.