PLA degradation

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1

You might have noticed at times that PLA can get surprisingly brittle.
Even just left in the teflon tube and coming from a sealed box it can just snap into small pieces.
Sometimes removing a few metres from the spool gives less brittle filament but sometimes the entire roll went bad.

I tried some dirt basic tests while using a lot of PLA for my prints.
A length off the new roll going right into a zip bag and another one into a zip bag with some blue beads.
Also a bit into a properly sealing glass jar and of course just out in the open air next to the printer.
Yes I also put some into a teflon tube and another with the ends sealed using some modelling clay.

Don’t know what I expected but the results were more confusing than defining.
Some samples got very brittle very quickly, some are still flexible and strong today - over 4 months later.
So I wondered if moisture, air and such are too blame or if there is much more to the issue we face at times.
I got reminded of this night vision scope I bought years ago that just kept draining the batteries during use within half an hour…
It’s soft outer shell turned into a sticky and almost slimy stuff just by being kept in the box…

UV is bad, we know that but why does PLA not behave like PLA when being tested?
Well, turns out matte PLA survives longer than standard PLA but silk can be either long lasting or going bad quickly, seems related to the level of shine.
So the additives play a role here…
Some might ‘evaporate’ or degrade over time, changing the properties of the filament.
Some might react to what is in the environment, like solvent fumes, cooking, whatever - we don’t know because we don’t know what it is the filament.
With the teflon tubes I noticed that it seems to be a myth that the teflon affects the PLA in a bad way.
Far more stressful is the banding in the tube.
Samples I got in there in line with the curvature lasted quite long while those I forced in the opposite bend direction cracked quickly.

Ever checked nice and clear PLA with some polarising films?
Nicely reveals any stresses like it does with glass…
Hmmm…
If ‘see through’ PLA shows stresses everywhere, what are the chances this is not the case for normal PLA ?
The stuff is rolled up at elevated temperatures so it all goes on nicely and won’t just jump off the roll once you free the end.
Quite the opposite, it snaps right back onto the roll.
Means it IS fixed in this particular state and changing it causes additional stresses.
Made me wonder about all those using re-winding as an option…
Ever tried warming the PLA up for this job, preferably in some controlled way?
And on the other end - how much does drying a roll of PLA affect this and those additives in the filament?

2

PLA is different from most other plastics. Nylon, for example, gets more flexible when it’s absorbed moisture. PLA, however, gets brittle when it absorbs moisture. So much so, it’s been known to break in to tiny pieces while still on the roll.

If you want to evaluate brittleness in PLA, you have to control for the moisture level in your samples. If they’re not all the same, your results will not correlate and your conclusions will be misleading.

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3

I did, more or less, including samples stored with desiccant and coming from fresh rolls as well as dried ones.
I wanted to rule out to usual moisture problems as I often experienced old PLA failing despite having been stored perfectly dry.
As you said, PLA IS different, being ‘organic’ and all that.
And with so many blends of it out there it is harder than ever to find just one source of the breaking issues.
I have a roll of PLA that is now about 5 years old, always stored in the open as I had no use for it.
Came with bubbles inside…
Despite all that it is still flexible, still resists kinking…
On the other hand I had to throw out 2 rolls after they were stored in a sealed box with desiccant for about 6 months.
They were stored with PETG but I doubt that made a big difference.
Just weird that there seems to be no consistency between brands and types of PLA.

4

Well, every filament blend uses it’s own mix of chemicals, and manufacturers all pretty much consider the specifics to be proprietary. So comparing different filaments is kind of a “fool’s errand”. You have no way to quantify the variables that matter. As you’ve observed, one filament might be extremely tolerant of environmental conditions, while another is not. I don’t think you’re going to find one rule that can be applied to them all.

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