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PLA- and PET- smoothing with dichloromethane CH2Cl2


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Posted (edited) · PLA- and PET- smoothing with dichloromethane CH2Cl2


Quick summary: dichloromethane (=also known as methylene chloride), formula C H2 Cl2, can be used to smooth the surface of PLA and PET, in order to remove or reduce layer lines, and seal tiny openings in-between the printed sausages, or seal mild underextrusion. Dichloromethane can also be used to bond PLA and PET.


Also see the Wikipedia info: https://en.wikipedia.org/wiki/Dichloromethane


Below you find a lot of photos of the smoothing-effect on PLA and PET, and of the bonding.




I just received a bottle of dichloromethane and did a couple of quick PLA-smoothing tests by brushing it on. Thus the cloakfiend-method (see his extensive tests and guidelines on the forum), but then using dichloromethane instead of acetone.


Dichloromethane works better for smoothing PLA than acetone, and makes a shiny surface, "glossification". But it is not as good as acetone on ABS. It is somewhat halfway inbetween those. It does melt the surface a bit, rounds sharp edges a little bit, and closes tiny gaps. But it does not totally remove layer lines on crude models (haven't tried fine models yet). Overdoing it, by leaving thick drops on the surface, causes molten material to ooze out. It evaporates equally fast as acetone, thus very similar in that regard.


I haven't tried vapour-smoothing yet. And obviously, I have no idea of the long-term effects yet.


Photos will come later, when I have more time and more light. I just thought I would let you know that this could be an option too.


Dichloromethane is easier to get than chloroforme, and does not require special permissions. But of course, being a strong solvent, it is poisonous as well, similar to acetone. And should only be used in well-ventilated rooms, such as a garage with open door, or outside. Or in a fume-extraction cabinet in a lab.


Edited by geert_2
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Posted (edited) · PLA- and PET- smoothing with dichloromethane CH2Cl2

Here are a few photos of before and after smoothing with dichloromethane.


Filament under test is only colorFabb PLA/PHA for now, because I have lots of old waste parts available for testing. Nozzle-size is always 0.4mm. Layer-heigts may vary between 0.1mm and 0.3mm (I don't remember for most parts, too old). Most parts are quite small, often ca. 10mm wide.


All tests were done by brushing-on. I haven't tried vapour-smoothing yet. Smoothing still continues a bit after the dichloromethane has evaporated, while the PLA is drying. So you need to stop a bit early. Similar to aceton smoothing on ABS.


It looks like multiple gently brush-ons, not too wet, is better than overdoing one big brush-on: too much liquids causes tears, and partial dullness, and more bubbles oozing out.


Generally, in the photos:

- untreated, original parts clearly show layer-lines, you are familiar with that

- mildly smoothed parts still show layerlines, but are far more glossy, and the "valleys" of the layer-ridges are smoothed

- heavily smoothed parts show very few layer lines, but get dull again if smoothing is overdone. Not only the valleys of the layer-lines are smoothed out, but also most of the tops.

- if smoothing is overdone, bubbles ooze out. Not sure why: the dichloromethane penetrating too deep, melting/liquifying material, and forming bubbles when evaporating on its way out? Maybe?

- dichloromethane penetrates quite deep: it shines through on thin plates

- if brushing-on: use a smooth brush, because a hard brush shows scratches

- the high-gloss of smoothed surfaces may show defects more than non-smoothed duller surfaces

- brushed-on liquid penetrates into seams and closes them of, bonding parts together, although I have not tested how strong the bond is

- also, brushed-on liquid closes gaps due to underextrusion. But don't overdo it, because then you get the effect of bubbles oozing out


Now the pics:


Original, untreated



Smoothed with dichloromethane. Notice the dark vertical lines, which are brush streaks, due to the brush that had hardened.



White bar: left=untreated, center=mildly smoothed, right=heavily smoothed






Heavily smoothed










Edited by geert_2
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Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

A couple more pics:





Smoothed, but overdone: see the dull area near the top



When overdoing, the holes shine through the bottom, indicating that dichloromethane penetrates quite deep into the plastic and keeps melting/dissolving it. These indents take some time to form.



Untreated text: this text is ca. 7mm high



Smoothed: it looks out of focus, but it isn't (the dust is sharp)



Untreated, close-up



Smoothed, close-up: notice the bubbles oozing out of the edge of the hole, where the dichloromethane pooled and overdid



Top 1/3rd untreated, bottom 2/3rd smoothed: although much smoother, it shows deformations better due to the high-gloss.






Bottom 2/3rd smoothed: notice how the liquid filled the gaps, and partially melted the material and bonded the parts together. I haven't tested how strong the bonding is.



So, that's it for now.





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Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

Still a couple more pics. All photos were taken with a Logitech C525 webcam, with a close-up lens in front of it.


For some applications, smoothing may be nice, but for others (such as fine text) the untreated prints may look better and crisper.


I don't know how the glossy surface of the smoothed areas would affect bonding of paint or plating later on.


Untreated text and smoothed text next to each other. The smoothed looks terribly out of focus due to the rounded edges.






Smoothed, but a bit overdone: notice the tear (dull area) near the bottom



Top part smoothed, bottom part not



Here the lower area is smoothed, and both are bonded by the liquid running into the gap.



Smoothed and bonded. Notice the bubbles oozing out here too. These plates are ca. 3mm thick.



And now that is it, as I ran out of photos.


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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    Thanks Geert for the effort and the pictures. 

    It works, but as you said not as good as Aceton and ABS, but maybe when you vaporize it, it gets smoother. 

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    Posted (edited) · PLA- and PET- smoothing with dichloromethane CH2Cl2
    17 hours ago, UbuntuBirdy said:

    when you vaporize it, there is only a small gap between a smoothed part and a totally melt down...


    Do you have any timing recommendations, to start from? Is it in the range of seconds, minutes, quarter hours, hours,...? My prints are usually 100% filled, and not too big (see dimensions below).


    Edit: and any idea about long-term side-effects? Strength, brittleness, dimensional stability,...?


    I have an old magnetic stirrer: if that still works, it could help distribute vapours evenly, so they do not accumulate on top or on the bottom of the jar, if their weight would be different from air.





    Edited by geert_2
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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    Because the gap is so small, the timings are different for almost every Pla brand... and that's why I stopped working with vaporized dichloromethane...

    I usually just correct a few imperfections with a brush, with only small local applications.

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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    Dichloromethane works for PET as well, and it is even more agressive: in one generous brush-on application, it removed all layer lines in my tests. See the photos.


    The outer layer stays soft for quite a while. Sometimes it gets a bit milky, but that goes away with time, and/or can be wiped off the day after.


    Pro: much smoother surface, no layer lines anymore. And internal features such as watermarks in transparent/translucent PET become better visible.


    Contra: the tiny bubbles... And the fact that I have no idea about long-term effects: deformations, changes in material characteristics,...?




    All photos: material is PET (brand ICE, from Trideus in Belgium), and layer thickness is 0.1mm if I remember well. Watermark text is 3.5mm caps height, 0.5mm leg-width, and sitting about 0.5mm inside of the model, thus hollow letters.


    Top one = treated with one generous brush-on application. Bottom one = untreated.



    Left area = untreated, right area = treated



    The bubbles... They start forming some time after the application. Looks like degassing in the still very soft, half-molten plastic. The CH2Cl2 is highly volatile, like ether.



    More bubbles in the treated one... The text is a hollow watermark, sitting about 0.5mm in the model.



    Smoothed part (top) looks better and is better readable from most angles.



    Left = treated, right = untreated



    Another view of the watermarked models.



    Another angle. Even though there are bubbles, the treated one (top) looks way better than the untreated (bottom). One application removed all layer lines. What is still visible, are the tiny gaps deep inside the material, in-between the printed sausages.




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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    A couple more smoothed compared to original 3D-prints. These are in translucent PET too. In real life the difference is even bigger, but it is hard to get on photo. The thumbscrew is standard nylon, M4 thread, 16mm wheel. Layer-heigth was 0.06mm.









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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    This can also be used for bonding PLA and PET. Or bonding can be an undesired side-effect if you are not careful enough. But I don't know if the bond will hold forever, how strong it is compared to the material itself, or if it is susceptible to shocks (like cyano-acrylates: they can be knocked apart) or to heat-decomposition.


    Here a few pics of the bonding.


    Also note that the smoothing removes layer lines, and seals underextrusion if not too bad, but due to the high-gloss and reflections, it might make the surface look rougher than the dull raw print before, in some cases (see the sphericons).

















    When rolling downhill, these sphericons roll straight down first, then take a sharp corner sideways and go back upwards a little bit, and then go down again,  repeating this zigzag cycle.


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    Posted · PLA- and PET- smoothing with dichloromethane CH2Cl2

    I thought I would add a few safety recommendations, as not everyone may be familiar with handling chemicals. (I have worked in the chemical industry with highly explosive and agressive chemicals, although very long ago.)


    When using chemicals like dichloromethane (=ethylene-chloride), ethylene-oxide, acetone, xylene, ether, and similar solvents, use good precautions.

    - Always use safety glasses. Not just any safety glasses, but the kind that look like diving goggles. So the spats can not fly parabolically behind it and still get in your eyes, as with normal glasses.

    - Always use good fume extraction, so you don't smell and don't inhale the chemicals. If unavailable, use it outdoors in the garden, or under an open carport. I have known 2 people getting cancer from inhaling xylene (another good solvent) regularly for prolongued amounts of time, disregarding our safety warnings, saying we were idiots.

    - Gloves might *not* be a good idea, contrary to popular belief. It depends on the glove-material. Most solvents go through latex and silicone gloves: silicone is watertight because it repells water, but it is definitely not oil-tight and not solvent-tight: they seep through quickly. That is why you need to impregnate a silicone mould with silicone oil first, before casting solvent-based two-component plastics. Then the solvents can not penetrate so deeply, extending mould-life. So, don't trust general-use gloves.


    If you get highly volatile liquids on your bare hand, such as ether, acetone, dichloromethane, ethylene oxide, xylene, and similar, they will evaporate immediately, feeling very cold. This may cause dryness and whitening of your skin. This is not good, but at least they don't penetrate deeply and don't do much internal damage, because they evaporate way too fast.


    However, if you wear gloves, and if the solvent would penetrate them (that is why they are *solvents*), then it can no longer evaporate and will keep penetrating your skin deeply for a very long time, maybe hours. This could do a lot of internal flesh damage and cause severe chemical burns. You may not feel these burns: some products like ethylene-oxide may take hours (sometimes up to 12h) before you become aware of the burns. But then it can not be stopped anymore and keeps going. And they may cause cancer on the long term too. I have known a guy who got ethylene oxide on his shoes, and even though it were "chemically resistant safety shoes", it seeped through and caused very severe burns, landing him in hospital for several weeks.


    So, if you want to wear gloves, be very sure that solvents can not go through. Don't use cheap general-use gloves.

    I always handle these products with bare hands, but I smooth only half of the 3D-printed part, up to a natural seam line. Then I let that dry, and do the other half. Or I hang the model on a wire, or on a screw, and dip it in the solvent. So I don't make skin-contact. If a drop spats on my hand by accident, it dries immediately. And I handle it in such a way that the fumes are extracted away from me (I have a fume-extraction cabinet in my lab).


    - Although dichloromethane doesn't seem to, most other solvents are highly flammable or explosive, and require only very little ignition-energy. Contrary to fuels like diesel or benzine/gasoil which require fairly high ignition-energy. Dropping a metal screw-driver can be enough to let some solvents explode (e.g. ethylene-oxide).


    Use any additional safety measures recommended by the manufacturers of the products.

    With such precautions, handling should be reasonably safe, and you can 3D-print smooth "hospital safe" models for medical use, without layer lines so they can be desinfected well. Smoothing is also very good for mould-making: it makes releasing the castings a lot easier.


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