There’s a lot of information out there regarding this topic, and the truth of the matter is that it depends on a lot of conditions, since in some cases PLA will become brittle and break down fairly quickly, while in some others it will last for years underwater without getting damaged at all!
In this article, I will go over if PLA will dissolve in water, what conditions need to be met for this to be the case, if it absorbs water, and how you can make it waterproof, if at all. But here’s the short answer if you don’t have time to read the whole thing:
In order for PLA to dissolve in water, a lot of conditions have to be met, such as a high water temperature, exposure to UV light, and the presence of specific biological activity. In most cases, PLA won’t break down or become brittle in water for years unless the temperature of the water is relatively high, or if sunlight is able to come in contact with it.
Will PLA dissolve in water?
PLA is a type of bioplastic. It is made from potato, corn, rice, and other similar plants and vegetables. Although it is water-resistant, it is not like other plastics made from petrochemicals which can last in water for 500-1000 years. PLA breaks down much more quickly in water than traditional plastics, and that breakdown can be sped up by certain environmental conditions.
Environmental variables that will influence how much a PLA 3D print dissolves in water include filament brand, processing additives, biological activities, and external variables including UV light, temperature, and the oxygenation of the water itself.
Pure water will not affect PLA prints. However, under the above mentioned conditions, it will start to degrade at a much quicker pace than other plastic types.
In addition to this, organic matter like bacteria and inorganic materials like mineral salts degrade the polylactic acid (PLA) polymer chains in impure water, causing them to break down into much smaller chains called 4 monomers. When the plastic gets to that size, microorganisms can start to eat it, which is actually called composting but is commonly mistaken as “dissolved in water”.
Therefore, if the necessary conditions or chemicals needed to decompose the biodegradable PLA are not present in the environment, your PLA prints will never be affected by water.
At worst, it will swell since PLA, as well as most other filaments, is hygroscopic, meaning that it absorbs water, but you can dry off the excess water and bring it back to its original state.
Does PLA Absorb water?
PLA filament is mildly hygroscopic, which means that it absorbs water (Slower than other filaments). This means that both the filament and the finished prints will swell up and become brittle over time. In order to avoid this from happening, you should store the PLA in plastic containers or ziploc bags with silica gel packets.
PLA absorbs water and will weaken when it does. The more moisture in PLA, the weaker it will become. A wet PLA print will have a rougher texture and more imperfections like blobs, bubbly texture, and stringing. It will become brittle and lose flexibility which means it will be more likely to break and less likely to bend. The adhesion between the individual layers of the print will also be compromised.
A wet PLA print can be brought back to its original form and toughness by drying it in a filament dryer, kitchen oven, or fruit dehydrator.
This is also why you don’t want to print with PLA that has been sitting in a humid room, since the printing process itself will be compromised and the results will be far worse.
So, always try to store your filaments properly, either in a sealed bag with moisture absorbers, or in a specially designed storing box.
How to make PLA Waterproof
I’m going to tell you four ways you can waterproof your 3D prints.
1) Print thicker layers
If you want to avoid leaks, you might want to try printing with thicker layers.
Printing layers that are a little bit thicker than average can reduce the chance of leaking for the simple fact that if the layers are thicker, water will have a harder time getting through because there are fewer spots where it could potentially penetrate.
The fewer interfaces there are in the print, the more likely it is that all liquid will be contained as there will be fewer places for it to leak out from. Just adding an additional 0.150 mm thickness, will ensure that the interfaces between your layers are as few as possible.
If you choose to use a wider extruder, you’ll be able to print layers that are thicker quite easily.
2) Over Extrude
Overextruding is an effective way to waterproof your print, but it does considerably reduce the visual quality of the outer shell.
You can waterproof 3D prints by slightly over extruding the filament when printing. It allows the filament to bond better with previously printed layers. It also works well with prints that were printed at a higher temperature as the layers are more likely to adhere to each other.
This solution may not work for you if you’re creating a product that requires very precise dimensions and that needs to look polished.
3) Add More Perimeters
Increasing the perimeters or shells of your model will waterproof your 3D print better without significantly impacting visual quality. It is possible to prevent leaking altogether by adding an additional 4-6 shells as they will create a strong barrier.
4) Print Less Complex Models
You can waterproof your 3D models very effectively by simplifying their geometry during the design process. The more intricate or complex your 3D print, the more possibilities there are for some imperfections to appear, and therefore there might also be more places for water to leak through your print.
Simplifying your model will help waterproof it and at the same time make it stronger, easier, and faster to print. When you have overhangs, sharp corners, or complex details in your design, there’s more room for error in terms of gaps and layer adhesion.
5) Use wax to make the Print Waterproof
Wax can help make your 3D print watertight, and you don’t really need any specific kind of wax, even crayons will work.
Make sure to clean the surface of the print using a small brush, then use a heat gun or a double boiler to melt the wax, or any other object you can think of that would melt it, and then using a brush apply it on the print.
After doing this, let it sit for a couple minutes until the wax has completely cooled down to finally remove the excess wax with the brush.
If done correctly, your print should now be watertight.
Can you use PLA objects in Aquariums?
PLA is a bioplastic. It is non-toxic, making it an appropriate choice for use in your aquarium, but there are some important factors to consider when using PLA filaments in aquariums to minimize harm to your fish or other aquatic pets.
PLA itself is safe, some PLA manufacturers use dangerous additives which can jeopardize an aquarium’s aquatic ecosystem. If you want to prevent PLA prints from putting dangerous chemicals in your tank you should avoid printing with PLA that’s not marked food-safe or that has not been reviewed appropriately for aquarium use.
Don’t print using any PLA filament that is a composite of materials like flex PLA, glow-in-the-dark and wood-fill. Choose the natural PLA or white PLA (which is clear and has a slightly yellow tinge).
PLA is biodegradable, so it will eventually decompose and the PLA plastic will break down and crumble away over time due to the unique conditions of the fish aquarium. This is especially true for saltwater tanks.
A 3D print made from PLA needs post-processing to keep from completely breaking down, such as waterproofing. Post-printing treatments are important for protecting the prints from decomposing. They also give them proper surface finishes.
Some people claim that in just two or three weeks, your PLA prints will completely break down in water. But there definitely is a lot of controversy surrounding this topic.
While PLA will become more brittle over time, this is mostly cause because of UV radiation, and not because of it coming in contact with water, unless the water is sitting at around 70 degrees Celsius. In this case, the prints break down quite fast!
So, essentially you can create prints out of PLA and use them in water, so long as they don’t get hit by sunlight all day long. I’ve seen PLA prints survive for over three years in water without any noticeable decomposition.
I hope this information was useful!
Have a wonderful day!