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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
    Commented Oct 28, 2016 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
    Commented Oct 28, 2016 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
    Commented Aug 26, 2018 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
    Commented Aug 26, 2018 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
    Commented Aug 26, 2018 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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  • $\begingroup$ "Overheated" for PETG in 3D printing would typically mean hours to weeks at up to 260°C. $\endgroup$
    – Technophile
    Commented Jan 16, 2020 at 20:36
  • $\begingroup$ I see for melting point "melting point of brass (900 to 940 °C, 1,650 to 1,720 °F)" and the temperature of red hot brass "525C -- 975F -- Red heat, visible in the daylight, 581C -- 1077F - Red heat, visible in the sunlight, 700C -- 1292F - Dark red, 800C -- 1472F - Dull cherry-red, 900C -- 1652F - Cherry-red". Presumably keep it down to dark red? $\endgroup$
    – Technophile
    Commented Jan 16, 2020 at 23:40
  • 1
    $\begingroup$ I admit that "red heat" was a little vague. What I meant was the one you barely see at the lower end of the temperature range. From the capabilities of my hot air gun (causing about the same 'redness' as my gas torch) I'd estimate that to something around 500°C, but of course not sure because I didn't check it with the thermal camera. $\endgroup$
    – oliver
    Commented Jan 17, 2020 at 21:32
  • $\begingroup$ As to getting 'overheated': weeks is certainly not true for the sample of PETG filament I have had. Don't know anything about its purity of course. Say 1 hour seems realistic to me (gets slightly brownish after a decent print job). $\endgroup$
    – oliver
    Commented Jan 17, 2020 at 21:35
  • $\begingroup$ Thanks for the temperature clarification! Re the 1 hour time duration, please clarify, seems likely we are talking about different things. Print duration often exceeds an hour (I did a 16 hour print recently, hardly exceptional). It seems to me that at least the average 3D printer enthusiast is unlikely to remove and heat the nozzle to red hot after every print, or interrupt prints every hour, so I must have misunderstood. $\endgroup$
    – Technophile
    Commented Feb 25, 2020 at 16:23

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