Mar 6, 2016 | By Andre

When it comes to 3D printing materials, they all differ in one way or another. PLA and ABS, two of the most popular materials used in the desktop 3D printer market might look very similar but in reality react different to external stimulus.

ABS has a higher melting point but also cracks easier on big prints under certain conditions. PLA smells nicer while printing but can’t be acetone smoothed like ABS can. And since PLA is corn based, it is also biodegradable and will degrade over time unless kept in dry spaces while ABS, being petroleum based, will keep its form for much longer.

But how much do PLA 3D prints really break down over time? If experience taught me anything about storing PLA plastic it’s that you can leave it out as long as you want and nothing will happen.

It seems others aren’t as convinced. Moisture-free filament containers have made their way to thingiverse and have even successfully funded on Kickstarter. Moisture in PLA, or so its said, is to be blamed for filament swelling, jammed hot-ends, steam forming while 3D printing and weaker overall 3D printer output.

I’ve never experienced such PLA related sorrow in all my years of keeping 3D printer filament spools out in the open but it seems the debate rages on thanks to a few accidental experiments and subsequent chatter on Reddit.

In late February of this year, a reddit user linked to his blog post suggesting he accidentally left a white PLA print in a jar of water in 2012 and forgot about it until very recently. To his surprise, it was discovered that absolutely nothing had taken place in terms of the PLA 3D print degrading in the water filled container.

But wait, Bill Waters, another blogger had himself an accidental experiment and the results were drastically different. In his case, he 3D printed a filter basket for his fish tank but wasn’t happy with the size so after a week 3D printed another one to use.

Having kept the first version out in the air while using the second one in his fish tank for a year, he was able to show how exposure to water broke down the plastic in one, but not the other. As the below photos show, the water-soaked basket had degraded rather obviously over the short span of a year.

So what’s the real answer when it comes to PLAs biodegradability? Even Bill Waters ends his post on an inconclusive tone after noting another PLA 3D print that was left in the same fish tank did not decompose in the slightest. He suggested that its possible that the amount of bio-matter flowing through the basket via its filter might have been more responsble for the material breakdown than the moisture itself.

At the end of the day, it seems as though moisture is to blame for some PLA based 3D prints breaking down but not for others. Factors such as temperature, light, biological activity, filament brand, pigment, processing additives and a whole slew of environmental variables can also play a role.

While skimming through the Reddit thread on the topic, user blargscar had a rather compelling point that stuck out to me more than the rest as making sense.

He writes that:

PLA will absorb water, meaning water molecules diffuse between polymer chains causing volumetric swelling. PLA will NOT be affected otherwise by pure water. When in the presence of certain compounds that are in soil, the polymer chains actually degrade into smaller and smaller pieces until they are (approximately) tetramers (4 monomers). At this size, the PLA can begin to be eaten by microorganisms in the environment causing it to compost. So unless these chemicals are present in the environment that the PLA is in, it will not be affected other than swelling, which can be remedied by drying it with desiccant in a box or through heating to a low temperature (<50C) and letting the water evaporate out naturally.

It seems like after all these years, people continue to get different results when it comes to PLA and moisture in the air as the primary catalyst to the material’s decay. Like I said, I’ve never witnessed any moisture based decomposition on any of my 3D prints or filament. I’ve used four year old PLA and it fed through my 3D printer and printed as if brand new. So I don't know, what do you think? If you have experience with PLA and its consistency over time, feel free to contribute your stories and observations as a comment below.



Posted in 3D Printing Materials



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the_minidude (ZA) wrote at 1/13/2017 8:26:41 PM:

After 3 years, all the PLA printed parts on my printer are breaking and falling off the printer. The printer is exposed to a daily dose of sunlight as it sits next to a window. The humidity fluctuates here between single and high double digits dependent on season. Summer it rains 5 days out of 7. Temperatures range from 8 degress celsius to 40. However, I'm pretty sure it's not the humidity or temperature that's the issue but rather the sunlight. I have an equivalent age roll of white ABS that I can no longer use as it is too brittle and some of my older printed parts in ABS are all suffering from becoming brittle. Mostly anything that has been exposed to UV. UV seems to be the biggest issue and by inspecting my printer more closely... the parts closest to the window are crumbling the most whilst some of the parts at the back of the printer sow no signs of aging (all printed the same time from the the same reel but degrading at vastly different rates, but all exposed to the same levels of humidity but differing levels of UV I've switched to using PETG as it just prints way better and easier than ABS or PLA once you get your settings right. It's incredibly strong with remarkable layer adhesion and suffers very little shrinkage and almost no warping. So if you want a solution to prevent your filament absorbing moisture or are worried about it's longevity, try a different type of filament. PETG is impervious to almost everything I've tried on it including leaving a part on the window sill for a year exposed to direct sunlight most days.

TC wrote at 11/28/2016 11:18:47 PM:

Can anyone tell me if a PLA printed model with withstand being a feature in a homemade snow globe (i.e. a mix of water and glycerine). Am hoping to do this with some children soon but don't want their models to degrade afer a short time! Any advice / opinions would be greatly appreciated!

Nathan wrote at 7/21/2016 6:48:19 PM:

Andre, Its great you haven't had any problems. But then where are you? what geographical location? What is the average temperature and humidity levels that the PLA has been in? (inside a temperate and humidity controlled building, or open and exposed to (outside) elements and day/night and geographic temperature swings. Again don't misunderstand, its great your having success, but without more information and details, there is no way to make any comparisons. Same too with the other data, if those who are having problems are providing their location and environment variables, their results aren't going to help anyone. Data, but data with context helps.

Bart wrote at 3/17/2016 10:08:46 AM:

I also use PLA in bathroom, moreover I like to take long and hot showers. After two years it didn't event turn yellow. I think humidity isn't enough to degrade PLA but a soil would do the job.

MadDavo wrote at 3/8/2016 7:52:11 AM:

The author of the article says he has not experienced the effects of humidity on PLA and that his PLA has not suffered any degradation by leaving it out in the open for extended periods. However, the author has not stated where he is located nor the typical atmospheric conditions to which his PLA is exposed at his location. I am located in Sydney which has a warm climate and is often humid near the coast. I find that the quality and printability of my PLA is GREATLY affected by humidity. Spider-webbing, brittleness, inter-layer adhesion, bubbling - are all affected on different PLA brands and colours to various degrees. All my PLA is now stored in air-tight containers with dessicant. Furthermore, I have taken to drying PLA using a food dehydrator before printing. I find the quality of prints is greatly affected by these mitigation techniques. The relative humidity at my location is commonly above 60%.

JuKu wrote at 3/7/2016 4:17:44 PM:

A printed hook for shower stuff failed at the point of most stress, while the rest of the part was fine. Maybe stress is a factor?

Julio wrote at 3/7/2016 2:34:29 PM:

Problem with the fish tank is the composition of water and the flow. It's not the same to leave a print in a container with no flow and mostly clean water than in a tank with a constant flow and chemicaly complex water with many degrading backteria. I agree, PLA is not so un-resistant. In fact, I've had much more trouble with ABS because of environment humidity.

scott macdonald wrote at 3/7/2016 1:53:30 PM:

I have at least 8 open rolls that i switch back to from time to time. it can be over a year before I use them again with colours like Green and Pink. In a room that i often have a lot of condensation close by on the window. I have not yet noticed any obvious change in the printing ability or size of the filament..

Koen wrote at 3/7/2016 10:18:14 AM:

One year into 3d printing I was curious about the bio degradability and designed the absolute worse use case for an pla object in my house. A toothbrush holder. This has been placed in our bathroom (temperature swings, high levels of moisture and exposure to air, stress by clamping a toochbrush). 3 years in the object is 90% ok. Small cracks appear on the stress points. Most likely the stress cracks would have appeared in a dry temperature stable environment.

Define your PLA wrote at 3/7/2016 9:58:33 AM:

Hundreds of manufacturers and colors, each with it's own little twist on exact chemical composition that probably even changes over time if you would use the same color of the same manufacturer for a few years... There is just no real baseline to make any sort of statement about biodegradation with the core parameters of filaments shifting all over the place. I've had filamants that already had problems beeing exposed to sunlight (UV) for a few years, and others seem to look like new even if they were abused with much more extreme exposure to the elements.

Syed, EZ3-India wrote at 3/7/2016 5:04:47 AM:

Same here, printed with 2 year old PLA filament and it still extrudes and builds like new.

Wonko wrote at 3/7/2016 1:01:34 AM:

Living in a dry climate it is not unusual for our humidity to be in the single digits. In fact it is not uncommon to have humidity levels in a home that would be lower than well kilned furniture. I don't believe that I have to worry much about PLA swelling. I would propose the Oreo test. If you can leave your Oreos out on the counter and they aren't a mushy unpalatable mess by the next day, you are probably good to leave your PLA out. If you live somewhere that you have to use a sealed cookie jar, or eat them within hours of opening, you had better protect your filament.

Buster Tap wrote at 3/6/2016 7:47:03 PM:

In our case, oil attacks ABS but the PLA just resists it. We have jigs and fixtures on metal cutting machines that have been in place for well over a year with no decomposition. ABS components have swelled and cracked in the same situations, attacked by the coolant.

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