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I work in 3D printing. One of the materials we use is polyethylene terephthalate glycol-modified, or PETG. It is a pretty good material, both in strength and appearance. It is melted and pushed through a "hot end" nozzle, typically either brass or hardened steel, at about 230 degrees C.

Unfortunately, it is rather sticky, and tends to accumulate on the hot metal surfaces, where it slowly degrades due to the heat. The resulting residue is black, and somewhat hard to remove. I have tried blowtorching it, which works with polylactic acid (PLA), but that just results in the same black substance.

I have seen recommendations to use either acetone, dichloromethane, or phenol. Other substances like toluene are recommended - some say they work, some say they don't. However, all of these seem to be recommended for dissolving/welding the plastic in its original form. There doesn't seem to be any advice for dissolving the residue after it has degraded from heat, at which point its chemical composition has changed.

From my research, the residue may be composed primarily of acetaldehyde. I was not able to find information (that I can understand as a lay person) about how to dissolve that.

So far, I've tried putting a brass nozzle caked with PETG residue into a 50C acetone bath for an hour. A little of it came off, but not much. The ideal solvent would attack the residue so completely that it would come off without too much force. The inside bore of the nozzles (the melt zone) is typically on the order of 1-2 millimeters, so the best option is to use an abrasive cleaning filament. Something tougher, like a wire brush, is not possible in that confined space, as far as I know.

If anyone has a good answer, I'll spread it around the 3D printing community, so you won't just be helping me. Thanks in advance!

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  • $\begingroup$ Do you know if the PETG is amorphous or crystalline? I was wondering if the heat exposure and rate of cool down might be changing the solid form on cooling. There are so many options to try it's hard to know where to start. For (fairly) innocuous substances, I would try DMSO, sulfolane mixed with about 5% water, silicone oil or a strong solution of lactic acid. I would try 350 cps grade for the silicone oil, it's cheap and not volatile. $\endgroup$ – Beerhunter Oct 28 '16 at 0:10
  • $\begingroup$ According to Wikipedia, PETG is amorphous. The plastic is melted quickly (less than a second) in the hot end, may heat further from friction as it is pushed out the nozzle (typically 0.4 - 0.5mm), and then it cools (either from ambient air temperature, or from room air being blown over it by a cooling fan). This doesn't generally cause a problem. However, small amounts often cling to the hot end nozzle and may degrade. Additionally, if the hot end is left idle (heated up but not extruding), it could potentially sit there around 230C for hours. $\endgroup$ – 626Pilot Oct 28 '16 at 1:05
  • $\begingroup$ If the residue comes from really long overheating, it might be partially carbonized. In this case it CANNOT be dissolved in anything except strong oxidizer that can eat metallic parts they come into contact with. $\endgroup$ – permeakra Aug 26 '18 at 23:41
  • $\begingroup$ Anyway! I'd try toluene, xylene and similar aromatic solvents. They might work. If they don't, stick with mechanical cleaning, unless you can use ceramic/glass nozzle. In THIS case I would consider some aggressive oxidizing solutions. $\endgroup$ – permeakra Aug 26 '18 at 23:46
  • $\begingroup$ Blowtorching is a nice option if your nozzle can survive it. If it can, use blowtorching without hesitation. It is easier and cleaner than any solution/solvent. $\endgroup$ – permeakra Aug 26 '18 at 23:48
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It is difficult to tell when you consider PETG overheated (how long? what temperature?). Thermal degradation likely produces several reaction products each of which having different solubility in different solvents. So I don't know whether I ever encountered "overheated" PETG during my own 3D printing experiments.

But I have had very good experience with Tetrahydrofuran (THF), which I happened to have in my basement for a long time (beware of peroxides!) and I have finally found an application for. It dissolves freshly printed PETG (and glue parts together) as well as the residues on the print nozzle.

Side notes: Acetone is wellknown for being absolutely useless for dissolving PETG and I can confirm this from my own experience. All you can expect is to roughen the surface a little bit.

You can read several reports that say dichloromethane is not working as a solvent for PETG. I have found a report that claims Cyclohexanone is working. But I haven't got personal experience with these both. Toluene neither.

But in general, the best method for cleaning nozzles is brute force, i.e. pyrolysis by bringing the (brass) nozzle to red heat with a gas torch. Fast (takes only a few minutes) and reliable (absolutely no residues, expecially at the nozzle hole). One thing I have noticed is that it is a good idea to polish the nozzle with finest steel wool after pyrolysis, especially the inside. On the inside this polish reduces friction for the filament (the brass gets "hazy" after heating it with the gas torch). On the outside, having a shiny surface may reduce emissivity/absorbtivity a little bit, which helps keeping set temperature during printing.

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