The best solvent to smooth PLA is 1,3-dioxolane.
At least according to my calculations 😅 (yeah I’m kind of a chemist who loves math).
Anyway, I won’t give you a lesson about why 1,3-dioxolane is the best solvent for PLA. You can go check this wikipedia page to know more about this solvent.
What you should know is:
- 1,3-dioxolane is commonly used in paint solvent formulation and dissolve a lot of polymers/plastics,
- This solvent is very good at dissolving many organic compounds and our body being mainly organic 🤪 it’s not suprising that this solvent can be harmful for your health. However, it is less harmfull (not CMR) than other solvents described in literature to smooth PLA such as THF or Chloroform. And thus, it deserves more attention.
There are many articles/tutorials written out there about post-processing techniques for 3d printed objects in PLA, but most of them do not highlight how good 1,3-dioxolane is to smooth PLA:
- 1,3-dioxolane is mentioned in a peer-reviewed article by Sato, S., Gondo, D., Wada, T., Kanehashi, S. and Nagai, K. (2013), Effects of various liquid organic solvents on solvent‐induced crystallization of amorphous poly(lactic acid) film. J. Appl. Polym. Sci., 129: 1607-1617. doi:10.1002/app.38833. However their conclusion is quite limited (quote: “PLA films are soluble in polar aprotic solvents”) and fail to highlight why 1,3-dioxolane is particularly a good fit with PLA.
- BrittLiv has written a very detailled 12-steps tutorial on instructables that I highly recommend you to read. It’s well explained and she mentions also safety concerns which are critical when handling solvents, even for those with moderate toxicity. However, she didn’t investigate 1,3-dioxolane for smoothing PLA, probably because this solvent is not easily available commercially. In this article I’ll give you a few tricks on how to get this solvent.
Safety First
Before I continue, I want to take the time to discuss about the safety concerns associated to handling solvent and especially 1,3-dioxolane.
According to its MSDS, 1,3-dioxolane causes serious eye irritation (H319) meaning you have to wear protective glasses and use it in well ventilated area.
Also, it is highly flammable liquid and vapour (H225) meaning you have to handle it away from any flame or ignition source and again in a well ventilated area.
So please protect yourself, wear your Personal protective equipment (PPE): glove, glasses and mask (you should get used to it with the covid19 situation around here 😉
Bad Matt is not protected to handle solvent (reading glasses do not count). 
Use specific gloves, a good respiratory mask and protective glasses. 
Good Matt is well protected to handle solvent.
Note: do not mistake 1,3-dioxolane with 1,4-dioxane. The names may be close, those are two very different chemical compounds with different polarity and toxicity!
How to get 1,3-dioxolane?
I’m familiar with two producers of 1,3-dioxolane:
- BASF is a global producer of chemicals and this solvent is part of their Intermediates division.
- Lambiotte is a producer of chemicals, mainly from the acetal chemical family. They are located in Belgium.
If you are a company and are authorized in your country to buy/handle/sell chemicals so you can probably contact these companies or their local dictributors to buy 1,3-dioxolane in bulk.
If not, you can look at product such as paint strippers. I hope by sharing this info with the community that we can identify more products containing 1,3-dioxolane.
The only commercialy available product I found containing 1,3-dioxolane is the Paint Stripper spray can from Montana. They do not advertise this product as being able to smooth PLA but as a general purpose paint stripper for graffity or DIY.
As you may know from my other articles on this blog, I’m a big fan of Montana paint spray cans for painting miniature scenery and terrain. That’s how I found out this product and I was quite happy to discover in the MSDS of this product that it contains 30-40 % of 1,3-dioxolane among other solvents. That’s not as good as pure 1,3-dioxolane but still I immediately thought it might do the trick (and it did as you will see below).
For my friends in France, you can buy this product on Allcity website.
For my friends around the world, I don’t know. Let me know in the comments if you find this product (or other similar products containing 1,3-dioxolane) in your country and I will update the list 🤗
1. Smoothing with Montana paint stripper spray
Here is a quick experiment I did using Montana paint stripper spray. For those following me on IG, I’m currently working on a Kessel game board for Star Wars legion and I needed some pipe connectors. I 3d printed a dozen “Industrial pipe components for Warhammer40k” by ComradeQuiche available here on Thingiverse and used it as a test for this experiment. This model has a curved shape that makes it hard to sand and was thus a good way to see how this paint stripper could affect the surface.
In term of 3d printing settings, I used an Alfawise U20 with 0.4 mm nozzle, 100 micron z layer resolution and Sunlu PLA+ filament.
The original untreated piece, a pipe connector with a curved shape 
I sprayed three layers of Paint stripper waiting a few minutes between each 
I covered the piece with a glass to slow dow solvent evaporation 
The piece after drying, the surface change to white due to partial solvent‐induced crystallization as described in literature 
To better compare I applied a layer of brown spray paint 
Left: untreated, right: treated with paint stripper
As you can see it’s far from being perfect but it definitely has an effect on the piece and I’m pretty sure with a more dedicated formulation we could have product specifically designed for 3d printed PLA object smoothing using 1,3-dioxolane.
2. Smoothing with pure 1,3-dioxolane
I also tried to use pure 1,3-dioxolane on another piece of the same model. In this experiment I simply dipped the piece in pure 1,3-dioxolane for 1 min.
Please note that when handling this solvent you need to use glassware and/or stainless steel only as it will dissolve most plastics. Pay attention if you want to use a brush as it can also dissolve most synthetic hair.
The original untreated piece, a pipe connector with a curved shape 
I poored pure 1,3-dioxolane in a glass cup 
I dipped the piece for 1 min 
The surface is way smoother, layer separation is less visible 
To better compare I applied a layer of brown spray paint 
Left: untreated, right: treated with 1 min in pure 1,3-dioxolane
3. Smoothing with mixture of 1,3-dioxolane + 7% PLA
Last experiment was to use a mixture of 1,3-dioxolane with 7 wt. % of PLA. I used misprints that I cut in small chunks and let it dissolve in 1,3-dioxolane overnight. Due to the molecular weight distribution of PLA, the solubility is partial so you need to shake it before use. This time I only did a quick 10 s dip of the piece in the mixture, then let it dry.
The original untreated piece, a pipe connector with a curved shape 
Quick dip of the piece for 10s (time to take the picure) 
While not as smooth than 1min dip in pure 1,3-dioxolane, the result is quite promising 
To better compare I applied a layer of brown spray paint 
Left: untreated, right: treated with 10 s in mixture 1,3-dioxolane + 7 wt. % PLA
As you can see with these three experiments, it’s far from being perfect and it’s more exploratory than anything. My objective is to share this info with the community to open new possibilities together. I’m sure we can develop product that are better adapted for post-processing 3d printed PLA objects. Imagine if we could have access to a whole range of paints specially formulated with 1,3-dioxolane. This would open up a wide range of application I’m sure in the 3d printing world. Let me know what you think in the comment ^^
Take care and happy making
Matt
PS: Here is the link to the instructable tutorial Smoothing 3d Print PLA With 1,3 dioxolane
Simple as WaR 
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