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I am trying to print a tank to be used with my RC engine. The material that I have to use needs to have the following properties:

  • It needs to be possible to seal the final print so that it is not leaking any fluid
  • It needs to resist methanol, nitromethane (a solvent like Acetone) and lubricating oil at room temperature. It can get discolored or have other changes from the fuel, but it must not be able to compromise the sealing.

I first - foolishly - just printed it with ABS as I do for every fluid container as I can nicely seal it with Acetone. After almost being done with it a friend told me to check the chemical resistance of ABS and as you might guess methanol and nitromethane completely desintegrate it, almost like acetone itself, so that was a waste of time/material.

Next I considered using Nylon. It shows exactly the chemical resistance against all the fuel components I need, however I could not find any (easily available) option to seal the print after printing and after printing a small test container and pouring in some water it leaks after half a minute, so unless I find a way to seal the Nylon containers interior this is also not an option.

I checked various epoxies but the few that I checked all showed poor resistance against methanol/nitromethane.

What I could not test yet but seems like an option is using HDPE. I am using PET bottles to transport the fuel sometimes so it definitely is both resistant and - in theory - watertight, however I am not sure how I can seal an HDPE print, so I am not sure about my first requirement with HDPE. EDIT: I found that Limonene dissolves HDPE and is relatively harmless and easily obtainable. Maybe it can be used to seal the HDPE print surface?

Hence my question: Is there a material that can be printed on a regular desktop printer (heated bed, nozzle up to 255°C) that satisfies both my requirements above or am I "doomed" to buy a moulded plastic fuel tank?

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  • $\begingroup$ PLA would probably do okay resisting the chemical (it's notably resistant to acetone and similar), but might not have the temperature resistance you need to sit next to an engine. $\endgroup$
    – Joel Coehoorn
    Commented May 25, 2021 at 21:44

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Most commercial blow-molded fuel tanks for model airplane fuel (methanol or ethanol, nitromethane or nitroethane, and some combination of castor, mineral, or synthetic lubricating oil) are made from HDPE. This material isn't commonly seen as filament, in my limited experience, but it ought to be possible to arrive at settings that will give a liquid tight tank without further sealing if you can find some. As you note, limonene might be used to smooth/seal HDPE prints, but likely won't be necessary if your settings are right.

You might want to test PETG filament for its resistance to your fuel mix(es) -- this material is available as filament, prints with settings little different from generic PLA (in my experience, higher nozzle and bed temperature, and a little more bed clearance for the first layer), with good layer adhesion and, with a good print, is liquid-tight as printed. It's not particularly flexible (as is the case with HDPE), but since you can customize the shape of your fuel tank, it may work for you -- or it may be more flexible in vase mode, as PLA is.

Sealing PETG may be as simple as baking it (similar to "heat treating" PLA to increase print strength, albeit again at a higher temperature) -- this partial remelting will ensure that layers are adhered throughout the print, which (presuming you have avoided under-extruded areas) should be all that's needed to make a printed tank liquid tight.

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  • $\begingroup$ What temperature can you bake PETG without distorting your print? $\endgroup$
    – Perry Webb
    Commented May 24, 2021 at 13:33
  • $\begingroup$ Great answer, I have already ordered some HDPE yesterday to tinker around and I did print a water container once with PETG but could not get it liquid tight from the print itself, however with much more experience now I might give it another go as I just recently ordered a new roll of PETG. Ill add another comment later with the results that I saw with both materials. $\endgroup$
    – Yanick Salzmann
    Commented May 24, 2021 at 13:45
  • $\begingroup$ @PerryWebb Not sure, haven't tried baking either PLA or PETG -- just seen it in videos as a legitimate fix for layer adhesion limitations. I'd probably start with the same amount hotter than recommended PLA baking temp as you use for printing -- that is, if you print PLA at 200 and PETG at 235, then bake your PETG 35C hotter than you'd back PLA. Bed it in salt and it'll be a little less prone to warp, too, especially if you can constrain the salt (tightly fill a can with a screw-on lid, for instance). $\endgroup$
    – Zeiss Ikon
    Commented May 24, 2021 at 13:48
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    $\begingroup$ After some tinkering with settings (5 wall lines, 5 top/bottom layers, ironing on top, 110% flow, 0.28 Layer height) I got a completely liquid tight print with PETG and it has been holding fuel for more than a day without any leaking or absorption, so the perfect solution. $\endgroup$
    – Yanick Salzmann
    Commented May 26, 2021 at 6:36
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As a supplement to the answer (doesn't fit well in the comments). This site https://www.filamentive.com/chemical-resistance-of-3d-printing-filament/ lists PETG has have a very high restance to alcohol, a high resitance to fuel

Is PETG UV Resistant?

In the long run, it is now a well-known fact that it will almost always come out on top when it comes to objects and builds that have to be resistant to ultraviolet (UV) radiation. I.e., UV resistant. This is why it is ideal for objects that have to be kept under the harsh mid-summer sun. This is because UV radiation has minimal effect on it as compared to PLA and ABS. -- From https://makershop.co/petg-uv-resistance/

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As a supplement: there may be a (flexible) fuel tank sealing liquid coating (or perhaps a liner?) that could be used inside the tank.

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