Hygroscopic Materials: Patience and Proper Storage Required
If you own a 3D printer you probably have heard about the importance of drying specific types of filaments, such as ABS, nylon, or PLA, prior to printing. The reason for this is that these materials are known as Hygroscopic polymers, meaning they will naturally absorb moisture if exposed to open air environments. That is why it is important these materials are vacuum sealed prior to shipping and include a desiccant pack. This means that these materials are usually ready to print when you first receive them, but once they are removed from their packaging, proper storage and handling become very important to ensure quality prints for subsequent uses.
If you have ever printed with a spool of Nylon 6 that was not properly dried after it was left out and exposed to open air conditions for a few weeks, you may have noticed some unusual results in your final print. So why does this happen? Although we may not see it directly with our eyes, we can certainly feel it in the summer and winter seasons. Humidity, or more precisely, water vapor which is often floating around in the air we breathe or air that comes in contact with our 3D printing filaments is a common condition for many manufacturing environments. The problem that humidity poses for 3D printing is that certain types of polymers (if left exposed) will have an affinity to absorb this water (in the science world we call this a hydrophilic polymer). Water that is trapped inside a polymer when it is heated will turn into steam (a gas) and expand greatly in volume, which leads to the formation of bubbles. These bubbles are often undesirable for the 3D printing process as it can lead to a rough surface finish, poor dimensional stability or stringing in the final printed part. Not only will the bubbles cause an undesirable surface finish, but the heated water particles within the polymer can also initiate a chemical reaction process known called hydrolysis. In short, hydrolysis is no good for the mechanical properties of any printed part. Heated water molecules inside a polymer can cause polymer chains to break, which reduces their strength which is why tensile strength, impact strength, toughness will all be negatively affected.
For 3D printing, the impact of water absorption with hygroscopic materials can of course be mitigated by drying the material prior to printing, however this process can be time consuming, require special equipment, and not to mention frustrating depending on how often you utilize these specific materials and how many printers you are running.
Hydrophobic Materials: Ready, Set, Print!
Finally, there is some good news, especially if you own multiple machines or a print farm. There are some new 3D materials on the market that do not have an affinity for water uptake (also called hydrophobic), meaning they do not absorb moisture internally into the filament or pellet, eliminating the need for drying. These non-hygroscopic materials include polypropylene, polyethylene, and a few others. The latest formulations as these materials have emerged as a viable replacement for many PLA, ABS, and Nylon applications. The unique combination of lightweight, chemical resistance, impact strength, and of course eliminating the need for drying are making these materials a favorite of service providers, start-ups, and hobbyist of all skill levels. It is also important to note, no fillers or additives are added to a achieve this, the polymer itself is inherently resistant to moisture uptake.
The overall manufacturing cost when utilizing these materials is also another big positive. When you consider the competitive price point of the material itself, and then factoring in the time savings of not having to dry the material, invest in drying equipment or change out spools that have been sitting for too long, the business case becomes very compelling. Imagine owning 20 printers and not having to remove spools after each use or paying to keep them in heated dry boxes. These materials can stay in an open-air environment for months at a time with no impact to the final print quality. For large format printers, there is no need to spend hours running pellets through a dryer, you can also easily store these materials in inventory at room temperature. No need for large, heated inventory storage rooms.
Regardless of which materials you choose, it is important to look at the overall value proposition of the material and how it impacts your operations. By taking a holistic look at your operation as there can be significant opportunities for optimization through proper material selection.