Starters guide to moisture, drying and filament storage

Author: Matt Tyson/Thursday, 25 October 2018/Categories: How To

Starters guide to moisture, drying and filament storage

Contents:

Introduction
Moisture
  Symptoms
Prevention, protection and storage
Drying
  Drying Times

Introduction

The quality of your 3D printing filament plays a significant role in the success of your 3D prints. Aside from using a reliable brand, it is important to handle and store your filament correctly to ensure consistent results through the life of the spool.

Moisture

A large majority of 3D printing plastics absorb moisture from the surrounding air which can significantly impact the quality of your 3D prints. These plastics are known as hygroscopic.

As the filament is extruded, moisture absorbed in the plastic will rapidly expand, boil and rupture, forming bubbles in the extruded plastic. These bubbles can have a significant impact on the surface quality, layer adhesion and mechanical performance of your 3D printed parts.

Gear on the left printed with Nylon stored in a dry environment, gear on the right printed with wet Nylon exposed to high humidity.

Not all materials absorb moisture at the same rate. When left in the open, plastics like PLA and ABS may absorb moisture over a matter of weeks or months while more hygroscopic plastics like Nylon and PVA will absorb moisture in a matter of hours or days. Of course this is not the rule and in workspaces with higher humidity or evaporative air-conditioning some material types will absorb moisture at a significantly faster rate.

If you have been 3D printing for a while, you have likely already experienced the effects of moisture, perhaps without even knowing.

Symptoms

When you extrude a length of filament, you may hear a popping sound or notice bubbles in the extruded plastic; this is a telling sign and easiest way to see if your filament has absorbed moisture.

Dry filament on the left extrudes normally, wet filament on the right extrudes with bubbles and a popping sound.

Moisture in the filament will also impact the print quality and performance of your 3d prints. When the moisture boils and expands in the filament, small bubbles will be created between each layer line while impacting your printers flow rate. This can have a detrimental impact on the layer adhesion and mechanical performance of your parts and in severe cases will directly impact the surface quality of your 3D prints. 

Other Symptoms:

  • With some materials, moisture can also introduce more printing artifacts like stringing. Stringing can be caused by printing with low retraction settings or a higher nozzle temp than required, so if your parts are stringing it may be caused by your print settings rather than moisture.
  • When filament absorbs moisture it will also become more brittle and easier to snap. Over time as the filament ages it will become more brittle regardless of moisture so this isn't always a sure fire indication of moisture. 
  • If the extruded plastic has a very rough texture rather than specific bubbles, in some cases this can also be a sign of moisture however extruding filament with a rough texture could also mean you have a blockage in the extruder or your extruders PTFE needs replacing.

Prevention, protection and storage

As the filament will absorb moisture in environments above 20% humidity, we recommend unloading the filament when not in use and storing your spools in resealable bags with desiccant to protect the filament from dust and moisture. Some brands will package their filaments in a vacuum sealed resealable bag which makes storage really convenient. Depending how long you keep the desiccant sachets, the desiccant will eventually need to be recharged or replaced to ensure they continue to absorb moisture effectively.

Materials like Nylon and PVA will absorb moisture at a significantly faster rate. In some cases these materials will absorb moisture over the length of a single large print so it is ideal to print these plastics directly from a dry box like the PolyBox™.

We use the PolyBox™ in-house as it effectively monitors and protects up to two spools of filament, storing filament below 15% humidity. By printing our hygroscopic filaments with the PolyBox™ dry spooling system and storing unused spools in resealable bags we can eliminate the effects of moisture and prevent irreversibly degrading the filament by drying filament excessively

Drying

If your filament has absorbed moisture, you can dry your spool in a convection oven or dehydrator. Time and temperature are the two commonly discussed factors when it comes to drying 3D printing filament however there will be factors out of your control like airflow and dew point which will impact the process.

Precautions Before Drying

  • Many ovens will go above the set temperature when heating so it is important to first preheat your oven before drying the filament.
  • Drying at the wrong temperature introduces the risk of softening and melting the filament or spool.
  • When drying for long periods of time there is the chance for heat to build up above the set temperature in areas of the filament, softening and fusing the filament.
  • To dry larger spools like 2kg / 3kg a longer drying time may be needed however with the chance for heat to build up when drying for long periods of time it may be safer to dry large spools with a longer total drying time, but by drying over multiple shorter increments.
  • Excessive drying can irreversibly break down and degrade the plastic.

Drying Time (1kg Spool)

The below drying times are estimates for a 1kg spool when using an accurate drying oven. Times may vary depending on the filaments water content.

PLA (most brands): 45˚C for 12 hours

PLA (Polymaker): 80˚C for 8h

PETG (most brands): 70˚C for 8h

ABS (most brands): 80˚C for 8h

PolyCarbonate: 80˚C for 8h

PolyMide™ CoPA: 80˚C for 12h

Repeatedly drying your filament will irreversibly degrade the plastic so after drying your filament, we recommend taking the prevention steps listed in the ‘protection and storage’ section which will eliminate the need to dry your filament and ensure your filament quality is maintained from the start of the spool to the end.

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