Keeping your thermoplastics dry is the first step to a successful print -- without it, none of your settings, adjustments, or troubleshooting will do any good.
Most thermoplastics (as opposed to thermosets) are hygroscopic -- meaning they absorb moisture from the air. Nylon is well known for this -- being a difficult, warpy material, it's also known for saturating with moisture very quickly, resulting in stringy, less-than-acceptable looking prints.
Nylon is hygroscopic, meaning that it absorbs moisture right out of the air surrounding the material or directly from water if it is submersed. The higher the humidity, the faster it will absorb moisture. Immersing nylon in water will cause it to absorb moisture extremely fast.
Moisture absorbed onto the surface of the nylon resin or part can generally be removed by drying for 3 or 4 hours. However, for moisture that has absorbed more deeply, a much longer drying time is needed, sometimes up to 24 hours or more.
Essentially, this is an issue only because we are melting plastic, and extruding it at temperatures above the boiling point of water.
When plastic is melted with moisture inside, the water molecules turn to steam, and create popping noises, and visible gaps or bubbles during the printing process. Absorbed moisture has been shown to act as a plasticizer, reducing the glass transition temperature and strength of plastic – which is a reversible effect.
This causes a ‘loosening’ of the molecular attraction which causes a reduction in mechanical properties and an increase in fluidity. The equilibrium moisture content (EMC) of a hygroscopic material surrounded at least partially by air is the moisture content at which the material is neither gaining nor losing moisture.
The value of the EMC depends on the material and the relative humidity and temperature of the air with which it is in contact.Because of all this, with almost all the high-performance filaments, like PEEK, PEI, PPSU, and PPS, the filament must be dried before processing (extruding)
Bake the filament spool at 120ºC for 12 hours, in a convection-style oven (toaster oven, conventional, lab or vacuum oven)
Use a pressure chamber to immediately pull -30PSI of vacuum on the spool, immediately after baking, while still hot, and vacuum for about 1 minute at -30 PSI, while agitating spool inside chamber(move it around, give it motion -- this activates moisture molecules and boils them off in the vacuum).
Next, move the spool to the chamber, and include desiccant in the chamber to absorb any extra moisture from the air. These materials soak up moisture very quickly (in minutes -- not hours). An advanced option is to run a line of Nitrogen or Argon into the filament chamber, maintaining slight positive pressure, forcing all oxygen/moisture out of the chamber. This allows for the longest print times.