CNC kitchen on drying with desiccant- https://www.cnckitchen.com/blog/cyo43tzz88uqge65xgwz0wv8yvv3rs
https://www.reddit.com/r/3Dprinting/s/q4ynPjmASl
This is everyone's monthly reminder that "Hygroscopic" and "Hydrophilic" are two different classes of material.
Hygroscopicity is a mechanical process and does not involve bonds that need to be broken. PLA filaments are hygroscopic, as are most thermoplastics. Think of it like a sponge soaking up water - it's just entering voids in the material.
Hydrophilicity is a chemical process that involves bonds that need to be broken. Nylon is hydrophilic, as is polycarbonate (slightly).
Both are important, as non-hydrophilic plastics like PETG and PLA can have strongly hygroscopic structures introduced by additives and the process of extrusion.
Heat is not required to reduce the water content of hygroscopic plastics, but it accelerates the process by increasing the vapor pressure of trapped water.
Heat is required to reduce the water content of hydrophilic plastic filaments. Bonds have to be broken.
No condescension is intended, it's tangled in a lot of jargon and is a bit of a nightmare to get clear info on.
( Fan, N. X. (2008). Mechanics of moisture for polymers: Fundamental concepts and model study. 9th. Int. Conf. - IEEE, 22, 1–14. https://doi.org/10.1109/esime.2008.4525043
Sperling, L. H. (2005). Introduction to Physical Polymer Science. John Wiley & Sons. )
https://www.reddit.com/r/3Dprinting/s/1ejli6Ju34 Hydrolysis causes irreversible polymer damage. You can dry it out a few times and not notice much difference. Performance degrades with every hydration and drying cycle, some H20 bonds on polymer surfaces, and dried filament has higher surface area. After around 5 years PLA stored in atmospheric humidity will become too brittle to print with, no matter how many times it's been dehydrated. Keep dry filament dry, or dry it then print it fast.
https://www.reddit.com/r/3Dprinting/s/8DG0zSL6Sf
Hi, I am a polymer chemist, and can shed a bit of light here. None of this is to say that the state of the filament isn't a contributor, or even the main contributor, to the problem, but there are legitimate chemical changes too. Water causes hydrolysis in the PLA backbone, which reduces the molecular weight of the polymer. Generally, as molecular weight of a polymer increases, the mechanical properties increase with it, so if it is reduced, so are the mechanical properties. There are two major ways this can happen; slowly over time, as PLA is fairly polar and interacts with water, so it will take some up over time, and the second would be when you are actually printing (processing) the polymer. The increased temperature makes whatever water is there able to hydrolyze much more quickly, so even if the filament isn't actually hot long, it takes much less time to degrade the molecular weight. I honestly have no clue what proportion of the problem each of those "pathways" has, so am not sure which would be a more practical problem, the storage, or making sure it is dry before processing.
I do have an off the cuff explanation for why drying could make it more brittle too, though. While water can cause the covalent bond breakage in the PLA polymer, it can also act as a plasticizer(which is often a desirable thing, but not in this case since the "plasticizer" is also able to degrade the polymer). This means that, only when the water is still actually present, intermolecular interactions between the pla and water can make the plastic more flexible (decreasing the modulus). When OP removed the water, I'm guessing it shined a light on the degradation that had already happened. I don't think the OP made a mistake by drying their filament. If they run it through their heated nozzle, my guess is the water would just compound the issue at the extruder head, they just wouldn't know it until they either had issues printing or had a brittle product.
If you have any questions or need any clarifications let me know, I'm happy to explain as best I can!
