Dissolving PLA (or not)

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Dissolving PLA (or not)

Postby orcinus » Thu May 09, 2013 1:43 am

Brace yourselves, this is gonna be a fairly long post.

I'm sure everyone's familiar with the Kickstarter project aiming to bring an automated 3D print finishing station to the masses. According to the authors, it works on both ABS and PLA. For ABS they use acetone, while for PLA they suggest using MEK - methyl-ethyl-ketone, also known as butanone.

Now, i've been hunting around for something that might dissolve PLA for quite a while. For finishing purposes, but things like nozzle cleaning as well. Here are some of the things i've found out:

1) DCM, a.k.a. dicloromethane or methylene chloride is proven to work and work well. There's one tiny downside - it's potentially cancerogenic and teratogenic (according to animal test data, but no studies on humans). It's also ingested and absorbed through skin fairly easily.

2) MEK, a.k.a. methyl-ethyl-ketone or butanone, was claimed to work, but according to many does not. According to the 3D Refiner people, it works in their machine because it's delivered as an aerosol and under pressure. I don't buy that, you'll hear why later. It's fairly safe, or perhaps slightly less safe than acetone (which is a normal byproduct of human metabolism). It's *possibly* teratogenic in rats, according to some studies (with a fairly low n).

3) Acetone does not work for PLA, pretty much according to everyone. Which is a shame, because it's the safest of the bunch and most widely available (cheapest too). However, i've had some luck with it despite what everyone seems to think about PLA's resistance to it - i use it to clean my heated bed and i've managed to smooth a print with acetone vapours once.

4) Sodium Hydroxide, a.k.a. caustic soda or lye, is proven to *break down* PLA, but not dissolve it. It will readily eat through PLA, given enough time and agitation (an ultrasonic bath works well), but it's useless for smoothing - it just hydrolyzes the PLA.

5) This article suggests using Weld-On #4 and #5. Both are methylene chloride based, so it's absolutely no wonder they're doing their job. What i'm finding interesting is that they don't behave the same due to other components by which their composition differs.

6) There were some mentions of xylene and toluene. Not much testing has been done, but as far as i know (they're common ingredient of garden variety paint thinners), they don't do a thing. I don't think anyone did any tests with vapours and high temperatures, though.

7) iFeelBeta a.k.a. 2printBeta used to have a PLA dissolving mix of their own, based on isopropyl alcohol, potassium hydroxide and aluminium hydroxide. Isopropyl alcohol does nothing. The rest more or less does the same lye does - it eats the PLA, it does not liquefy it so it's absolutely useless for smoothing (but good for stripping PLA-based support).

With that out of the way, let's move onto issue #1 - MEK vs. DCM. As it turns out, most people in the RepRap and MakerBot communities keep confusing DCM for MEK over and over again. Even i did it at the beginning. They are two completely different solvents - i can't stress this enough. They behave differently, their toxicity is different, their smell is different. One does really dissolve PLA, the other does not. The industrial solvent 3D Refiner people are suggesting (Kleen Strip branded, if i recall correctly) is actually DCM (plus some other things), NOT MEK. MEK is not a "high strength industrial solvent" as some label it, nor is it insanely toxic or cancerogenic (at least according to data thus far). It can cause eye and respiratory tract irritation, but hey, which organic solvent can't?

Now for issue #2 - is acetone useless for PLA? No, it is not! But it doesn't do the same thing it does to ABS. Not nearly. The reason i can use it to clean my heated bed is - i'm using it on a hot heated bed! The reason my smoothing test worked (sorry, no photos, i've destroyed the test object before i could test it) was because i've kept it in HOT acetone vapours. Depending on the purity of the acetone, behaviour can change too. With too much water in it, the PLA will likely crack and split. If it's fairly free of water, it will work, and the best way i can describe its effect is - it lowers the PLAs glass transition temperature by A LOT. It softens it so it's soft and maleable at room temperatures.

Curiously, for some filaments this is enough to get them smoothed out, while for some it doesn't do much.

In case you're interested in the solvents mentioned above, here's where you can find them:
1) DCM - some paint thinners (check the labels) - sometimes available in bulk for mixing proprietary thinning and cleaning agents, not available at all in some states and countries (due to its health hazard status)
2) MEK - nail polish removers (check the labels) - curiously, sometimes you'll find it (in a mix with acetone and isopropyl alcohol) in nail polish removers labeled as "oil-based" (and no, they don't mix MEK with oil, at least i never found such a product)


DISCLAIMER: Be extremely careful when experimenting with organic solvents. They typically have a very low flash point, meaning they'll ignite VERY easily. You could just lose an eyebrow, or you could burn the skin off your face or damage your eyes. They are also strong irritants, so use them in well ventilated areas ONLY. Some are highly toxic, so avoid ingestion by any means - that includes the skin.
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Re: Dissolving PLA (or not)

Postby orcinus » Thu May 09, 2013 1:57 am

And now for some photos...
Three days ago, i've let some PLA bathe in MEK to see what will happen:

Image

Left bottle contains a bunch of gray PLA (Natureworks 4032), the right one a single piece of Ultimachine silver (Natureworks 4043, i believe).
Two days later, i've checked up on the first MEK bottle. This is what it did to the gray PLA:

Image

Not much, right? Well, not exactly...

Image

Here's the silver PLA. Note the "scratches" - those were made by light fingernail pressure:

Image

I've then soaked the silver in acetone for one extra day. Note how the fingernail cuts expanded and smoothed out somewhat:

Image

And yes, it bends as easily as the "soft" PLA that's been making the rounds lately:

Image

Finally, the most interesting aspect of the MEK/Acetone soak:

Image

That's the same bit of filament, stretched to about 5/3 of its original length just by pulling on the ends.
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Re: Dissolving PLA (or not)

Postby cozmicray » Thu May 09, 2013 4:48 pm

Weld-on #5 seems to do it but is discontinued and contains some nasty stuff.

Weld-on #5 contains:
Methylene Chloride(75-09-02), Glacial Acetic Acid (64-19-7), Methyl Methacrylate Monomer (80-62-6)

I have seen posts on net that shows it works, but also needs about 12 - 24 hours to work.

It would be nice to have a solvent to clean up PLA.

So far I have used heat --- a torch!

And nylon even worse!
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Re: Dissolving PLA (or not)

Postby orcinus » Mon May 13, 2013 1:37 pm

The nastiest stuff in WO #5 is methylene chloride.
WO #4 contains it too, as does pretty much any other product that successfully dissolves (not breaks down) PLA, unfortunately.
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Re: Dissolving PLA (or not)

Postby DonaldJ » Mon May 13, 2013 7:11 pm

Riddle me this:

If one of the big marketing points of PLA is that it's bio-degradable (it's made from corn starch!), why is it so difficult to dissolve? There's been some heavy chemistry thrown at it. Do you need bacteria or microbes?

I noticed that no acids were used. How about something approaching stomach acid (HCl, muriatic acid)? I'd try it, but I have no PLA.
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Re: Dissolving PLA (or not)

Postby orcinus » Mon May 13, 2013 7:35 pm

Oh, breaking down (degrading) PLA isn't a problem.
Acids shouldn't work, i think, but lye will do that. Even water will do that, given enough time.

There are also enzymes that can eat it rather quickly or in a very controlled and timed fashion (it is for those reasons that it's a pretty useful material for temporary implants or growth matrices, from what i've read).

Dissolving it in the sense of "reversibly liquefying" it, the way acetone dissolves ABS, now *that's* a problem...
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