I’m not going to really rehash things in depth from my prior post An in-depth look at why some filaments become brittle - #7 by Ken-N-Texas
But the big thing to note with that post is basically the brittle some of of us is seeing in some filaments is it becomes brittle over time. I researched the issue, listed sources in the post, and basically it comes down to an additive (plasticizers) evaporating off the filament. This additive is used to make the filament flexible and without it or it being in a too low amount. The filament becomes brittle. Heating it up helps for a short bit during printing. But depending on how bad it is, it might be impossible to print or it will break right after it is done printing.
Since then there has been some questions on this and I was able to research this more. Note I’m still learning about this. It is extremely hard to pull all the info on this and you basically need to know exactly what to look for.
What filaments has this problem?
PLA and PVC. PLA is generally worse for this issue.
In the raw state, PETG, ABS, ASA, TPU/TPEs, and Nylon doesn’t have this problem. Note this is focusing purely on additives leeching from the filament, and not brittle due to other things.
How long do I have?
This is a major unknown. The problem is manufactures don’t let others know about the “special sauce”, and then even if it came out the ratio, what it added, etc changes over time. Like the problem isn’t just knowing the additives to add flex. But other additives and how they might react with the ones we need for flex.
To be honest, if I had the money, resources, etc. I would push for this to be figured out. Basically have a team study this, NDA used, and then use it to figure out why some filaments last longer than others, and so on. But ya…
What is known is some colors are more of a problem than others. But it isn’t an always. For example, black is a color many run into problems with. But at the same time with some batches, the black can actually last way longer than other colors. And without knowing the “special sauce”, it’s largely an unknown on why.
Does storage matter? Can a vacuum bag help?
The higher the temp, the more of a problem. Storing the filament in a freezer plasticizers will still evaporate. It is just slowed down some. The rate is hard to say because of the “special sauce.” Putting it this way, unless if your freezer can get down to -273.15°C, then you can’t stop it. BUT, if you do want to slow it a freezer WILL slow it down by a lot. 40-50 times compared to typical room temperature conditions. Note I use the following to figure out the 40-50x
k = A * exp(-Ea / (R * T))
Note the math can be wrong, but at the end. It shows there is a reduction.
The problem is you MUST vacuum bag your filament if you do this otherwise you will deal with condensation. And this means you need to let the filament come to room temperature before using it.
For those wondering about if freezing will damage the filament. No, and it can extend the life of it. Studies have shown that freezing PLA filaments, specifically at temperatures as low as -24°C, successfully stops the natural physical aging process of PLA for an indefinite period without affecting its mechanical properties or structural integrity.
Natural Ageing of PLA Filaments, Can It Be Frozen? - PMC (note the study focuses more on the polymer’s own internal molecular rearrangement and not on the additives leaving it. Additives which we are focusing on with this post and is needed for flex)
But with that it needs to handle carefully because it becomes brittle due to the cold. Which again is another reason why you need to bring it up to room temp before using it.
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Vacuum bag
This is an iffy thing.
The vacuum environment itself can paradoxically accelerate the volatilization (outgassing) of plasticizers from the filament. This is because the reduced pressure inside the bag creates a strong driving force, pulling these volatile compounds out of the filament matrix. Therefore, the vacuum does not slow down the rate of plasticizers leaving the filament; rather, it encourages them to leave.
So a vacuum bag actually increases the rate it is loss. There is no known practical method for consumers to reintroduce lost plasticizers into brittle PLA filament to restore its original properties. There is industrial methods.
For the net release of plasticizers from the filament to significantly slow down or effectively “stop” (i.e., reach a dynamic equilibrium), the partial pressure of the plasticizer vapor in the sealed headspace of the container would need to approach its equilibrium vapor pressure at that given temperature (typically 25°C for ambient storage). For the net transfer of plasticizers to slows down, the partial pressure of the plasticizer vapor in the sealed environment would need to reach these extremely low pressures, typically in the range of fractions of a thousandth of a PSI (e.g., 0.0000058 PSI to 0.000044 PSI), or even practically 0 PSI for some plasticizers.
ELI5:
A vacuum environment accelerates the loss of plasticizers from filament due to the strong pressure gradient. However, once the concentration of plasticizer vapor in the sealed space reaches equilibrium with the filament, the rate of loss slows dramatically. In contrast, storing filament in an open room allows the vapor to continuously escape into the surrounding air, preventing any buildup that could slow further outgassing. This means you’re not benefiting from any equilibrium effect in open-air storage.
- The vacuum increases the initial rate of plasticizer loss.
- The slowdown happens only when the vapor pressure of plasticizers in the container approaches equilibrium.
- Open environments never reach that equilibrium because the vapor disperses freely.
Why is this important? Some people put their filaments in and out of storage often. Remember, each time you put it under a new vacuum it doesn’t have the plasticizers gas to slow it down. So each time you do this, it losses it’s protective barrier. It isn’t going to make or break anyone, but it is important to note.
Note there is some escape when it comes to this. This is a known problem with these systems and why sealed filaments can become wet over a long time. Like if water can get in, then guess what can get out.
But what if you want to do pressured containers? Like the vacuum does hurt it some, but what if you use a pressure container to prevent this from happening?
This is possible, but you need the pressure to be hundreds to thousands of PSI. This is the range where scientific studies have observed a noticeable hindering effect on molecular diffusion and outgassing in various polymers due to the physical compression of the material and the increased resistance to molecular escape. Basically a range that is completely unrealistic, and likely would cause even more damage to the filament and yourself.
What to look for when it comes to wetness?
The following is a project I’m working on. I took some bad filament and splice it with other bad filament. I forgot to check if one of the ones was wet, and it turns out to be. But this gives a perfect example of what to look for. As it shows what a dry filament is like even if it brittle and then it starts completely having problems as it goes into the wet filament from the splice.
This is a close look at 1 of the strands. I took it off and a close picture to show the bubbling. This is signs of wetness.
Basically when you see this you need to use a dryer.
My advice from my last post still stands.
- Measure the weight of the filament.
- Dry
- Measure again.
If there is some weight loss, then repeat. If the filament is still brittle and there is no weight loss, then it is likely the above that is the problem. And it is better to try to find a way to use it now as it is only going to get worse.