I was noticing on a print I had just done that the quality was not up to typical snuff. I had just started using a roll of PLA filament that I had been keeping on a shelf without a wrapper for a couple months. How long can you store filament before it gets too hydrated from the air to print? I expected more than a couple months but perhaps I am wrong?
In theory, most filaments don't go bad within a year. However, praxis shows, that averse conditions can impact the filaments over time and age them to unusability.
Among the damaging factors is heat, but most filaments also are hygroscopic and absorb water to some small degree, or even heavily like Nylon.
As a result, it always a good idea to at least try to store filament dry. To enforce this, some use racks in a well-heated room, others are blessed with very dry weather overall. And on some locations, like the coast, you might even be forced to use dryboxes for each and every filament to try to slow the degradation of steady hot humid air leaching out the additions from the filament.
Dryboxes can keep the filament reasonably isolated from the surrounding air and so prevent moisture interacting with them to some degree. It is also a good idea to store them out of direct sunlight, as UV light might destroy color and/or the plastic. More information on why to use them is for example at this question
But fear not: most filaments - PLA included - can be freshened up again if the damage is not to prolonged! Baking them at a low temperature or storing them in a dehumidifier has worked in some climates. For PLA, keep the temperature at below 80°C. A couple of hours should get some the moisture that has seeped in out again. The Quality might not get back to that of fresh filament in all cases, but you might at least regain reasonable to good printability.
Also note, that different filaments are differently affected. ABS for example is a little less hygroscopic than PLA, while HIPS is one of the least hygroscopic filaments available.
I expected more than a couple months but perhaps I am wrong?
It depends on the filament, the shipping and the local conditions. I'm on an Island, so very high humidity.
We have several useless spools that never worked out of the box. They were shipped seafreight from China and had a couple of months journey. Only 2 spools out of 10 were useable.
With other filament seafreighted from Australia for 3 weeks filament here seems to last about a month at best, with 4 days being the lower limit so far. This is despite being kept in an airconditioned room most of the time.
We have had limited success with drying them out.
The answer is that it depends on the climate you are in or the climate in your house. The more humid, and the higher the temperature, the faster the moisture is taken up in the filament (note also that 40 % RH on a warm day has much more moisture in the air than 60 % RH on a cold day).
I have obtained a spool of filament that has been left in the garage for a few months, this spool has taken up so much moisture that it has become very brittle (unspooling will break the filament). Note that once the filament has taken up moisture, you could de-hydrate it, but it will never reach the same properties anymore as the moisture will change the molecules (shorten them), once broken they will not fuse by hydrating. It will however get rid of the water content so that there will be no steam bubbles when you print the filament.
Note that there are many types and brands of PLA, each with their own formula. The quality of the PLA has improved much over the years, implying that the moisture intake also depends on the brand and time of purchase. It is therefore very difficult to answer your question with a specific time frame, it could be months, but it could also be a week.My largest printer is located in a room where occasionally laundry is being dried, and although there is only a little ventilation, the large spools of PETG do not take up the moisture of the laundry. Basically, the moisture saturation is also depending on the type of filament.
To answer your question: it depends on the relative humidity. Generally, a few weeks in a semi-arid environment. But, it'll still print really well. If you're looking for really tight filament diameter tolerances, a week or even less could change the diameter .001 or more if there is moisture in the air. I've used PLA that has been exposed to air for a few months and it's been fine, but with small issues.
If the filament has absorbed too much moisture, you'll typically hear popping coming from the hot extruder as the water is burned off at the nozzle. Sometimes steam comes out of the nozzle when printing as well with "wet" filament. Usually, you can still get great results even if it has absorbed moisture. If the filament diameter has been affected significantly, (if it jams, or the water keeps the plastic too cool when it's coming off the nozzle) you can dry it out in an oven for a few hours like @trish suggested. I keep my filaments in a plastic bag with desiccant inside a big storage bin. Probably overkill but my water softener is in the same room and introduces moisture to the air, and my a/c blows right at the setup.
Dust is probably worse because it can accumulate much faster and cause jams.
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