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I know that it's said the PLA becomes brittle when kept in a humid environment, but my case is slightly weirder:

I have rolls of 1.75 mm PLA that I bought years ago and they are fine. But if I leave my spool fed inside the PTFE (Teflon) tube of my 3D printer, that part that is inside the PTFE tube, and only that part, gets brittle. The filament spool is always (even when stored) in open air.

Is it still the humidity that somehow is better kept inside the tube, or is there a weird reaction of PLA with PTFE?

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  • $\begingroup$ I have this exact problem, and mine is in a dry box. $\endgroup$
    – user77232
    Jul 23, 2021 at 14:28
  • $\begingroup$ I don't have a dry box. Filament spool is always (even when stored) in open air. $\endgroup$
    – Nicu Surdu
    Jul 27, 2021 at 11:38
  • $\begingroup$ I have the exact same problem with a PLA roll that is 3 years old. Breaks in the PTFE tube, but only if it has beend inside the tube for 1-2 days, the rest of the rest of the roll prints just fine. Any update on this? $\endgroup$
    – Stiefel
    Apr 30 at 17:03

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I'm having the exact same problem - it is enough to leave the filament inside the PTFE tube for an overnight and the next day the filament inside the tube is so brittle that I'm not even able to eject the filament without disconnecting the tube and getting out all small pieces of filament manually... but from my experience, it affects only cheap PLA filaments (like Creality ST-PLA) - I never had such issue with other types of filaments (ASA, PETG) or higher-quality brands of PLA (e.g Fillamentum, Filament PM...).

BTW - there is a video on YouTube demonstrating the same issue:

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  • $\begingroup$ Hi Dominik and welcome to SE.3D Printing. SE websites are driven by questions and answers, your answer is more a forum style "Me too" comment to another question where you ask for help to start a discussion. This is not what the answer section should be used for. Please read the help center, accessible through the button with the question mark at the top right menu. Please take the tour and also have a look at the questions and answers to understand how SE works. $\endgroup$
    – Greenonline ♦
    Nov 27, 2021 at 16:18
  • $\begingroup$ Apologies for the standard comment above. However, your post doesn't really answer the question, and will probably end up being deleted. You could post answer question, and refer back to this question using the URL - however, as you say, you have the exact same issue, so it would end up being closed as a duplicate - unless you add why the proposed solution (in the other - partially incomplete - answer) didn't work. Or a place a bounty on the question. $\endgroup$
    – Greenonline ♦
    Nov 27, 2021 at 16:26
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I have this exact problem as well. I am feeding filament from the dry box through the tube into the top of the hot end. After approximately 2 days I would notice that the filament is broken somewhere close to the hot end. I don't believe that it's just humidity.

I suspect that the filament being brittle and being made to conform to the PTFE tube's shape, having been recently on a spool, is causing the breaks.

As a result, I'm going to write a small script that will heat the hot end and eject 200 mm of filament every so often.

EDIT: Whilst the script works, the filament would just break somewhere else lower down in the tube. Therefore the amount of filament that would need to be extruded periodically would be just wasteful. A better solution would be to unload the filament, either manually or automatically (somehow).

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  • $\begingroup$ I don't have a dry box. The filament in the open air doen;t get brittle, wile the one in the PTFE tube does ... $\endgroup$
    – Nicu Surdu
    Jul 27, 2021 at 11:37
  • $\begingroup$ Did your script work? If so, can you post it in the answer..? $\endgroup$
    – Greenonline ♦
    Nov 27, 2021 at 16:23
  • $\begingroup$ @Greenonline, no because the filament would just break somewhere else further down in the tube. It's not a practical solution. I suspect that I would have to have some sort of "unload" mechanism, to retract the filament into the dry box. $\endgroup$
    – user77232
    Nov 29, 2021 at 14:53
  • $\begingroup$ That's a shame. Thanks for the update though :-) However, does that mean that your answer isn't really a solution (apart from your suspicion of the brittle filament)..? BTW, could you edit your answer and add that last bit of info in your comment to it? Thanks. $\endgroup$
    – Greenonline ♦
    Nov 29, 2021 at 15:00

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