Does humidity degrade PLA filament?

I have recently started having problems with printing PLA - the nozzle gets jammed. I have put this in another area of the forum [forums.reprap.org] but it suddenly occured to me that tall of the sympoms could be explained if my PLA filament was degrading in such a way that higher melting point crystals were forming in the PLA and these were blocking the nozzle.

All of my rolls of PLA have been open for some months and my printer is in a garage where the humidity is about what you would expect.

Any thoughts?

Mike

I can set the oven in my kitchen to low temperatures. I have dried my PLA by putting it into the oven at 50 degrees C for three hours with success. My wife doesn't like it much though!

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

I know that PLA will degrade with humidity, but the question I have is will this degradation cause blocking of the nozzle?

Mike

I'm not sure PLA will actually degrade at room temperature with humidity. "Degradation" implies a chemical change to the molecular structure. PLA will certainly absorb water since it is hygroscopic. You should dessicate it prior to using it if you're worried about that. Also, I have read that water will hydrolyze PLA at melting temperatures (much like pyrolizing, a.k.a. burning, but with the attachment of hydroxyl groups).

If sufficiently hydrolyzed, I'd imagine it could clog your hotend.

Edited 1 time(s). Last edit at 10/10/2013 11:19AM by iquizzle.

Ah! now we are getting places. Previously there were too many possible reasons why my nozzle is now getting clogged but didn't before. Reasons like: Stepper motor torque reducing (possible loss of magnetism with time/temperature); changes in current from the Pololu driver; Unrecorded changes in speed, temperature or other parameters in the print; new points of friction or stickage of the filament in the feed path to the hot end. Not to mention bit-rot in the code and being abominated by some deity and many other reasons that I have not thought of.

My experiance seems to chime with those of others on these forums, and other clues that there may be something going on here are found in the wide range of reports about any given hot end. Perhaps PLA changing with time has helped to muddy the waters.

Picture showing PLA from a freshly cleaned nozzle and after a few hours of printing with strange spiral pattern.


Picture showing yellow inclusions in PLA from a nozzle giving lots of back pressure.


To investigate this I will try cutting two good lengths (ca 100M) of PLA and bake one out in a fruit dryer at 50C for 5 hours and compare the prints.

Hopefully I will be able to avoid sacrificing to the Great Zog and the Flying Spaghetti Monster.

Mike

Hmm, no luck with drying the PLA. There is negligible difference between two prints - with and without drying. Not only that, but it is now happening with ABS.
As I have run drills down from both ends there should be nothing to block it. I made and used a variety of nozzles to this design without this progressive blockage before so I will make up a replacement.

Mike

Maybe it is dirt clogging your nozzle, have you thought about using a sponge or cloth clamped on the filament to clean it and wipe off any dust or particles before going in to the extruder kind of like this?

Nice idea Josh_mp5, but I have solved it. The problem was a plug of plastic which had built up in the hot end - every time the hot end was stripped the PTFE liner was changed - and each time the gap got bigger, finishing at about 2mm.



All is back to normal - except I have disturbed every setting in the book and will now have to recalibrate.

Mike

leadinglights Wrote:
-------------------------------------------------------
> Nice idea Josh_mp5, but I have solved it. The
> problem was a plug of plastic which had built up
> in the hot end - every time the hot end was
> stripped the PTFE liner was changed - and each
> time the gap got bigger, finishing at about 2mm.
>
>
>
> All is back to normal - except I have disturbed
> every setting in the book and will now have to
> recalibrate.
>
> Mike

This is why I stick the ptfe all the way up to the nozzle exit

quote 'This is why I stick the ptfe all the way up to the nozzle exit '


pfte needs to be held in place, likely by an extruder wall, or better a threaded insert. this can be made of metal because if hot zone is built correctly this end should never be much more than room temp.

which brings me to another discussion. fan should always be partially blowing on the cold region of extruder. else get a separate fan.

Edited 3 time(s). Last edit at 10/17/2013 04:59AM by jamesdanielv.