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I'm a maker and I've been interested in 3d printing for years.

I have found a technique for dissolve the PLA supports in a model printed in 3D in HIPS

  1. I have printed the model in HIPS and the support in PLA
  2. I have put the 3D model in a ultrasonic cleaner in the solution with water and sodium hydroxide

(1 liter H2O + 200 grams NaOH)

The PLA has dissolved after 3 hours with temperature 65° and 1 hour of ultrasonic sound.

I attach a youtube link with a similar experiment

https://www.youtube.com/watch?v=uWYn5wJ72zY

Is it possibile use another substance / solution less dangerous and less toxic?

In theory, the PLA is biodegradable. Is it correct?

Ps: I want use this combination of materials HIPS for model and PLA for Support.

Thank you in advance for the answers.

enter image description here

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    $\begingroup$ Ethanol? (And what is toxic here?) $\endgroup$ – Karl Sep 30 '17 at 18:22
  • $\begingroup$ Hello, I know that sodium hydroxide is dangerous for vapor. $\endgroup$ – Emanuele Sep 30 '17 at 19:21
  • $\begingroup$ I have tried with denatured alcohol in temperature 23° but didn't work. Do you mean pure alcohol for drink? What temperature? $\endgroup$ – Emanuele Sep 30 '17 at 19:24
  • $\begingroup$ by dangerous do you mean hazardous? $\endgroup$ – A.K. Sep 30 '17 at 19:33
  • $\begingroup$ Yes, I mean hazardous. I have tried a lot substance: Petrol, Acetone, trichlorethylene, denatured alcohol. But unfortunately no one worked. :( After I discovered that the sodium hydroxide can solve the PLA because has Ph basic (14 Ph). Do you think there are another substance? $\endgroup$ – Emanuele Sep 30 '17 at 20:20
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When I started 3D printing I did some trials to dissolve PLA. I tried acetone, caustic and some other solvent. The only one that worked very well at room temperature was methylamine in water.

Unfortunately, it is not a product to use at home. Caustic is corrosive, but the vapours of methylamine can irritate the eyes and the respiratory system. It should be used in a fume cupboard.

It is very effective because instead of a saponification, the amine reacts with the ester forming an amide, which is much more efficient.

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alphonse is right: What you get with NaOH (or KOH) is not dissolved PLA, but a solution of saponified lactic acid. The good news is you can just pour that down the drain as long as we don't speak of many liters per day and your sewage gets treatment and doesn't just flow into the next river.

You can calculate the amount of NaOH needed from the mass of the PLA printed. I'll leave that little stochiometric exercise to you, just use a reasonably small excess of NaOH.

With any organic solvent (if it works), you will soon sit on liters of waste for which you have no legal and affordable way of disposal.

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Simple Solution to Dissolve PLA is THF (Tetrahydrofuran) whose preferred IUPAC name was changed in 2013 to oxolane. It is used in the Pool industry, as well as in 3D Printing, and vinyl printing (like Vehicle wrapping)

See https://en.wikipedia.org/wiki/Tetrahydrofuran

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It is true that a mist of aqueous sodium hydroxide can be hazardous to eyes or lungs (or other mucous membranes, even skin when present in large amounts for extended periods of time.) (It is not true that NaOH vapor poses any significant risk at or near room temperature, including at 65°C) My first suggestion would be to stop the use of the ultrasonics, and try gentle stirring instead. If you must use an ultrasonic bath, then it should be sealed to prevent leakage of the mist into unprotected areas. There are many other chemicals which can provide a high pH. I doubt your explanation that it is simply the pH which "dissolves" the PLA is correct. Na+ will react with PLA to form the salt in a de-esterfication reaction. It is possible that KOH may be more effective, either on a mass or a cost basis - you'd have to try it. The most obvious high pH chemicals are NaOH, KOH, and Ammonia (NH4OH/NH3(aq)). You could try mixed salts such as Sodium bicarbonate or sodium biphosphate to increase the metal ion concentration (there are also known catalysts for the desterification reaction, one well known one is iron (but many catalysts may discolor the plastic). De-esterification also occurs in acidic conditions. You should consider the use of sulfuric acid or acetic acid (perhaps even hydrochloric acid) as well as the bases I've mentioned. In either case (acid or base), any residual contamination (due to poor rinsing or even absorption by the remaining part) can cause various structural and aesthetic problems over time. Be warned. To answer your question in general (I do not have any specific experience with PLA), NaOH will be quite effective, it is unlikely that other possible bases,(lye, dry lime, CaO, Ca(OH)2 is another one you could try, I just recalled it), or even KOH will improve your situation. CaO has obvious advantages in terms of both waste disposal and possibly for effects of aging, but it is also less soluble than K/Na hydroxides, so might be more difficult to rinse away, and it may not result in equally effective decomposition. (And note that your principle waste problem is the PLA waste.)

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    $\begingroup$ Would you mind structuring your answers a bit? You always write terrible text-worms. $\endgroup$ – Karl Sep 30 '17 at 23:09
  • $\begingroup$ I'll bet the calcium salt of lactic acid precipitates and gives a horrible slime. Don't. $\endgroup$ – Karl Sep 30 '17 at 23:29
  • $\begingroup$ Ok thanks, I think will try also CaO. But maybe NaOH make less residues. You have wrote that I can put together NaOH the Salt or sodium bicarbonate is it correct? In my solution, what quantity of Salt or sodium bicarbonate I can mix in (1 liter H2O + 200 grams NaOH) Thanks everybody for the advice. $\endgroup$ – Emanuele Oct 1 '17 at 18:47

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