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I was considering printing some pieces for my irrigation system, like tube connectors and such. I am aware that PLA is hydrophilic so I was wondering with what kind of product I could coat the pieces, non-toxicity is a requirement because it will water edible greens.

So, what kind of non-toxic product can I use to coat PLA to make it hydrophobic?

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    $\begingroup$ Amazon sells this food-grade epoxy material smile.amazon.com/dp/B01J16MYSE but you may find it difficult to coat the interior of your connectors evenly $\endgroup$ – Carl Witthoft Apr 27 '18 at 15:05
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    $\begingroup$ clear coat acrylic (quality clear "spray paint") forms a durable water-tight surface on anything you spray it on. $\endgroup$ – dandavis Apr 28 '18 at 10:13
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Before worrying too much about the hydrophilic properties of PLA, it might be worthwhile to test a fitting.

First, print a fitting and see that the freshly made print is strong enough to carry the pressure of the water, and the compression force of hose clamp you may need to connect the stiff irrigation hose to the printed fitting.

Second, soak the printed fitting in water for month or two, perhaps at an elevated temperature to match the higher ground temperature in the summer. You could put the part in a closed mason jar and leave it in the sun. You might add a little salt and fertilizer to the water to simulate ground conditions.

After this aging process, you could test to see if it withstands the pressure of the domestic water system.

You might also measure the ground temperatures where you intend to use the fittings. I find that PLA has no structural strength above about 150 degrees Fahrenheit (65 degrees Centigrade), and the inability to resist slow plastic may start at an even lower temperature. [For example, I print structural PLA parts with negative clearances and then dip them in 160 degree F water to soften them.]

If the printed fittings are strong enough but suffer from water absorption, I would either print them of ABS or coat them with an ABS coating. To make the coating, dissolve ABS in acetone until it is the consistency of thick cream, dip your fitting in the mixture, and allow them to dry. It will take longer than you think it should to dry, and the solution will take more ABS plastic than you might expect.

ABS is not generally considered to be "food safe", but this isn't a potable water system. The FDA lists ABS as conditionally food safe, and I would be comfortable using it to irrigate my lawn and vegetables.

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  • $\begingroup$ As I won´t use it in a lawn but for my pots, im using 5v pumps which don´t put much pressure on tubes, also if they are durable enough I can reprint them once in a while but still coating seems a good option to me. $\endgroup$ – Petar Petrov Aug 4 '18 at 0:14
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PLA will biodegrade over time. ABS would last longer, and stand up to higher temps.

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  • $\begingroup$ Yeah but its toxic, and I don´t have the enclosure for printing at those temps. Plus I don´t have ABS. $\endgroup$ – Petar Petrov Aug 8 '18 at 22:37
  • $\begingroup$ There are probably enough toxins in the soil, that it wouldn't matter anyway. There are toxicity issues in all filament. You don't know what charming extras the manufacturer put in there. You could also consider Nylon filament. $\endgroup$ – EvilTeach Aug 9 '18 at 13:14

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