July 28, 2016
All plastics, including 3D printing thermoplastic filaments, are polymers. Polymer science is a vast and complex field, but it’s fairly easy to understand what a polymer is. A polymer is a material made up of multiple repeating monomers. That probably sounds like another language, so let’s put it in terms of a material you are likely familiar with – PVC.
PVC, which is short for Poly (Vinyl Chloride), is a material made up of multiple vinyl chloride molecules joined together in long chains. Vinyl chloride is the monomer, and there are many of them, thus, ‘poly’. Easy enough, right?
In fact, most of the time, the “P” in a material abbreviation stands for “Poly”. Common examples include:
Now, you likely have come across the terms ‘copolymer’ and/or ‘copolyester’ when looking at filaments for your 3D printer.
A copolymer is simply a polymer made up of more than one monomer. ABS is probably the most familiar copolymer. It is made up of 3 monomers – Acrylonitrile, Butadiene, and Styrene. Specifically, ABS is a terpolymer, because it is made of 3 monomers, but ‘copolymer’ covers everything comprised of more than 1 monomer. Other examples would be Taulman’s line of Nylon copolymers – 618, 645, Bridge, and Alloy 910.
A copolyester is formed when PET, aka Polyester, is modified. Copolyesters have gained popularity as 3D printing filaments recently – PETG, PET+, Colorfabb XT, nVent, nGen, and T-Glase are all copolyesters.
Now that we have a basic understanding of what a polymer is – a long chain of monomers - it’s time to talk about water and a process called hydrolysis.
When monomers are joined together, it’s called polymerization. This is not a one way street, though. Polymer chains can degrade and be broken down – or depolymerize - and there are various ways that this happens. One of these ways is hydrolysis. Hydrolysis is when a water molecule breaks a polymer chain. All sorts of complex chemistry occurs when polymers hydrolyze. We’re not going to get into those details, but the material properties are affected when hydrolysis occurs (they are changed anytime the polymer chain length is decreased or increased) – loss of tensile strength, change of clarity, etc.
When you extrude filament that has absorbed water, the water in/on the material vaporizes and creates air bubbles and voids in the strand of filament. This can break apart polymer chains (shortens them), weakening the material, and it creates voids in the strands of filament which weakens inter-layer adhesion. It also leaves an undesirable surface finish.
You may not know it, but it’s likely that you have already experienced the effects of hydrolysis on your 3D printed parts.
This is Taulman Bridge nylon. The left was dried before printing. The right was not dried. These were printed with material from the same spool.
The print on the left was dried before printing while the print right was not dried.
We dried the spool on the left in a vacuum oven before printing, and then left material on the right to sit out for 2+ weeks.
The dried nylon is fairly transparent. The wet nylon is nearly opaque. It may not be clear in the image, but the dried nylon has a smooth, glossy finish, whereas the wet nylon has a rough, textured finish. Both objects are tough, but the wet nylon is considerably easier to pull apart at the layers (You can also see that nylon tends to warp – regardless if it’s wet or dry).
This is MatterHackers Pro Series PETG. The left cube was dried before printing, and the right one was allowed to sit out for 2+ weeks.
The left cube was dried before printing, and the right one was allowed to sit out for 2+ weeks.
As you can see, there is a clear difference in surface finish and texture. It’s hard to tell in the picture, but the dry cube is glossy. It has a consistent finish from top to bottom. The wet cube is textured, with a satin-matte finish. The texture is where air bubbles left voids.
Wet PETG is significantly more brittle than dry, and the interlayer adhesion is significantly reduced.
Fortunately, most of the filaments we print with aren’t very susceptible to hydrolysis at room temperature without the presence of an acid or a base. They are, however, very susceptible to hydrolysis when heated to extrusion temperatures. This means that we don’t have to worry once a part has been properly printed, but we do need to take steps to prevent hydrolysis when printing.
Since many of the common 3D printing materials are hygroscopic (they readily absorb moisture from the air), we must take steps to both dry our filament and keep it dry.
Nylon, polycarbonate, and copolyester filaments are all very hygroscopic and susceptible to hydrolysis when printed in the presence of water. Nylon and PC can absorb enough water in 48 hours to ruin prints.
The easiest way is to extrude some filament and watch it come out of the nozzle. If you see any bubbles, hear any hissing/popping/cracking, or see steam coming off the filament, then it’s definitely wet and needs to be dried out.
This video shows the clear difference between wet and dry nylon. (This was Taulman 645 nylon)
If you have nylon, polycarbonate, or PETG and the spool has been sitting out for more than a day or so, then you likely need to dry it. PLA and ABS are also susceptible, but it takes quite a bit longer for them to absorb enough water to cause major issues.
There are a few ways to dry out filament and keep it dry.
First, it’s important to dispel a common myth. You cannot effectively dry filament out by storing it in an air tight container with desiccant. You can keep filament dry this way, but in order to properly and thoroughly dry it once it has been saturated, you need to actively dry it.
The easiest way to dry filament is to bake it in an oven. Convection ovens work very well as they constantly circulate hot air around the spool. This is essentially how the raw resin pellets are most commonly dried – hot air is passed over and through the raw resin pellets before they are extruded.
There’s really only one important thing to know before baking your filament. You must preheat your oven and allow it to reach the set temperature before putting the filament in. Ovens work the same way that hot ends on 3D printers work – with PID temperature control – and it’s common for ovens to overshoot the target temperature a bit. This doesn’t really affect food, but it definitely can ruin your filament by fusing the filament together and/or melting the spool that it’s on.
1) Preheat your oven to 160-180F. (Fahrenheit, not Celsius)
2) Place spool in oven for 4-6 hours
3) Remove and place in an airtight container, preferably with desiccant. 5-gallon buckets with airtight lids from local hardware stores work very well for filament storage. You can use uncooked rice as a cheap desiccant.
Filaments with lower glass transition temperatures (Tg) like PLA, use lower temperatures to dry. Lower temperatures also require more time to thoroughly dry.
That’s really all that’s necessary to dry out your filament and ensure optimum material performance and surface finish.
So if you have some spools that have been sitting out for a while and aren’t printing as well as they used to, dry them out and try again. Chances are they’ll be like new.
As always, Happy Printing!
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