Brittle PLA filament

After the printer sitting unused for several weeks with a spool of PLA Basic filament mounted, I found that the filament had a break in the feed tube.

Pulled out the end still attached to the reel. I removed the tube and found a second break in the remaining piece. Most concerning was that the pieces were very brittle.

The end of the section still on the reel was brittle also.

I would estimate that about 5" of filament from the hot end back was brittle, while the rest of the filament in the tube seemed ok.

?? Any idea whatā€™s going on here?

K

Some filaments fair well but some will go brittle over time when they absorb enough moisture, older and/or cheaper filaments particularly suffer from this. A session in a dryer can rescue some, it canā€™t hurt, Iā€™ve had odd spools that Iā€™ve taken a dozen winds off before I came onto ā€œfreshā€ filament that wasnā€™t so exposed.

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I take it we are talking about PLA ?

PLA does not like moisture and it does not like getting too dry either.
Both could be the case if not used for a long time and left in the tubes.
I had an old roll, stored in a sealed bag with silica gel that was unusable after about a year.
Couldnā€™t even get it off the roll without breaking.

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Well, now, that is interesting. Like probably everyone else by now, Iā€™ve heard the exhortations about how itā€™s much better to drive the moisture out of PLA before printing, but this is the first time Iā€™ve heard that PLA being too dry could also be a problem. Up until I read that, my plan was to dry PLA and then store it in a sealed container at as close to 0% RH as possible.

Any rules of thumb as to how dry is too dry? What minimal level of RH should I aim for?

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If you mean this in terms of printing PLA than really dry (under10%) is best.
But the filament does not get extremely brittle if it is bone dry - it does so over time.
And from my old rolls I know that having a high moisture content, like when a bag had a hole, makes the filament brittle as well, especially if you than try to dry it.

Comes down to aging I guess.
For a printed part this is no issue as the plastic already underwent changes during the extrusion.
A bit like bending an annealed copper rod - as new quality PLA.
Have it tempered and hard and trying to change the bend makes it crack.
From what little I can observe I would say it is mainly the outer most layer of the filament that turns brittle as glass.
The inside still seems to be flexible, not that it would help LOL

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Thanks for the replies.

Yes, PLA Basic-- Bambuā€™s own brand.

The weird aspect is that the break and brittleness occurred only inside the PTFE feed tube. The rest of the reel, exposed to the environment, appears to be unaffected.

The printer had been off, so no locally generated heat.

K

The AMS feed system does put very small indents into the filament which can weaken the filament and give it a stress point for it to fail. You can feel the feeder indents in the last part of the filament when if you remove it from the AMS. Not saying this is the root cause but it is good to be aware of this.

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Is it in an area where it could have gotten UV damage? When I think of plastic becoming brittle, itā€™s on the suspect list.

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?? No. Inside the house, inside the PTFE tube. 70 F room temp, 30% humidity.

Is it possible the PTFE itself has an degrading effect on PLA?
Or UV light gets through the PTFE tubing causing that section to become brittle.

I learned recently, that PLA is not influenced much by moisture, but UV kills it. Was it exposed to sunlight? Then this would be my first bet.

Could it be that itā€™s breaking inside the PTFE tube because being more straight than on the spool is effectively stress too? My guess would be that when itā€™s being spooled in the factory while still fresh and warm the spool shape becomes its ā€œresting shapeā€.

As for the cause, I saw some youtube video (donā€™t remember which channel sorry) that mentioned it can also be an issue when thereā€™s a moisture difference between day and night (like in a garage). That repeated cycle can cause damage.

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Thatā€™s a very good point.

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I have seen a few rare people suggest that it can get too dry, but I wonder how true that actually is. If that was the case, I would probably have some major issues because I dry all my filament until it stops losing weight. But I havenā€™t hand any issues that would indicate Iā€™ve dried them too much.

One place I read suggested that drying it over and over again would eventually cause it to lose certain heat sensitive chemicals that could effect the printing and cause it to get brittle. The drying over and over again part seems a little more plausible, but I am still doubtful.

I bought flashforge adventurer 5m Pro, it came with a sample spool of PLA burnt titanium, 250 grams.

After setting up printer and initially using some Bambu PLA, then anycubic PETG, I open the sealed bag of sample PLA. Printed a couple items no issues.

Hadnā€™t used the printer for a day and noticed the filament linked just outside feeder tube. Weighed filament, dried for ~12 hours at 105Ā°. Lost a gram of moisture. Didnā€™t make a difference.

Feed filament in tube, felt it catch a couple places but otherwise went on to extruder. Went to print something last night and noticed filament again snapped just outside feeder tube.

Grabbed some Bambu to install and it feed in the tube like butter, pushing out broken pieces of the FF PLA. Pretty sure thereā€™s no rescuing this sample filament.

I loved the color but would be leary to purchase an entire roll now

I use PLA now for more years than I can count.
With that comes having experienced literally every filament problem and failure you can imagine.
Brittle PLA that just snaps during printing is not just a total pain but also produced sub-quality prints as the base material has gone bad already.

I have no UV getting into the room with my printer, donā€™t use any with exposed filament either.
So while UV is degrading to PLA it probably isnā€™t the factor here.
What is though is the degradation of the filament itself.

Even a tiny amount of moisture inside PLA filament reduces the time it can be stored without quality losses.
Most plastics age and those we use for printing are formulated specifically for that purpose.
If a sealed bad of beads is recommended to be used within 2 years and within 6 weeks after opening we should not expect more from our filaments, especially hand rolled off cuts sold as samples.

I found a roll of 3mm PLA in some old box, still with a strong vacuum seal.
Couldnā€™t even unwind it by hand without literally breaking up into tiny bits and pieces.
What still makes wonder today is what really happened to protected filaments.
In the early days of 3D printing when moisture in filaments started to be of concern it was proposed to coat hygroscopic filaments.
And the idea did not stay at this stage, for a short while coated filaments were on offer.
Never had a chance to try as there were no shipping options to where I am.
They applied like a polymer coating that is heat sensitive.
In the melting chamber it blends with the filament.
They claimed ā€˜patents pendingā€™ but once it all disappeared as quickly as it popped up I could not find any patent related to it and no filament manufacturer since then even tried.
Imagine living a really humid part of the world and not having to worry about drying your filaments - wouldnā€™t it be niceā€¦

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PLA is hygroscopic but not that bad like nylon or ABS. The thing is, water molecules get in between polymer chain and break long polymer chain into short polymer chains. Even when you drive water out, the damage is done and cannot revert. This makes PLA degrade and become brittle.

I come to believe the more heat cycles PLA went through the more degrade it be. I read somewhere the recycle PLA filament must be mix 50-50 old and fresh PLA but still the performance poorly. So yeah, PLA filament does have expiration date.

I guess, once you let the genie out of the bottle, you should make use all of the wishes before the genieā€¦ expires =)

I think it really depends on brand and maybe on color.

When I started with an Ultimaker 2+ 10 years ago, I bought a big bunch of Colorfabb PLA/PHA rolls. I still have some of them, that have been open since I bought the printer. They still print like at the first day without any drying or other consideration.
The roll that came with the printer was complete garbage after 1,5 years. It was a silver PLA.

So I think there is no general rule.

So oddly enough, seems like this probably isnā€™t a moisture problem. Found a reddit thread from 2 years ago that referenced another site. (sorry, doesnā€™t seem like I can post a link here to the story, but google ā€œwhy does my PLA filament keep breakingā€ and use common sense in selecting the best result and youā€™ll find it)

This guy did an experiment and found that just being in the PTFE tube can cause PLA to go brittle as quickly as overnight! This is exactly what Iā€™m seeing, where the filament in the tube breaks into dozens of tiny pieces, but the exposed spool of filament (on my A1 AMS-Lite) is just fineā€“still plenty bendy and doesnā€™t break.

Iā€™m wondering if thereā€™s a way to get the AMS-Lite to ā€œparkā€ the filament all the way back instead of leaving it in the ptfe tubes? (ideally, automatically when unloading and not a big manual effort!). Yes it will take more time to load, but not significantly.

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Thatā€™s interesting, Iā€™d love to see the link.