Does Acetone Dissolve PLA?

by | Feb 15, 2021

Yes, acetone can dissolve PLA but only under certain conditions. You might get better results with other solvents, but there isn’t one that reliably works for all PLA filaments.

PLA is an excellent 3D printing material, but it does not offer a lot of post-processing options. After all, sanding PLA prints to make them smooth is a lot harder than smoothing with a solvent, like in ABS with acetone.

The question is – would it be possible to use acetone to smooth PLA prints via dissolution? If not, is there any other solvent that achieves the same objective?

chemical solvent

When Do We Need to Dissolve PLA

To quickly answer this question, let’s look at how ABS benefits from being soluble in acetone. With this unique characteristic, You could smooth ABS print via acetone dissolution. You can subject ABS to an acetone vapor bath. The process takes just a few minutes and requires little effort.

In contrast, the most popular way for smoothing PLA is sanding. Although technically simple, this is a process that takes a lot of time and manual effort. If you had to dissolve multiple PLA prints, you would surely appreciate having a less tedious alternative using a solvent.

PLA dissolved in an appropriate solvent can also be used to weld two PLA pieces together or fill in gaps or cracks. That is the same concept as in ABS, as ABS filaments can dissolve in acetone.

Being able to dissolve PLA can also come in handy when cleaning nozzles clogged with PLA residue. If you have leftover PLA in your print bed, a suitable solvent can also help as a cleaning aid.

Considering how heavily acetone is used for solvent in 3D printing, it is worth exploring how it can dissolve PLA. Should that prove unsuccessful, are there any other solvents that we can use?

Is PLA Filament Water-Soluble?

With any discussion involving solvents, it is always worthwhile to consider water as an option. Commonly referred to as the “universal solvent,” water is a highly polar molecule that can bind to a wide range of compounds in a process called hydrolysis. However, how long this process takes will depend on several factors.

In the case of PLA, its water solubility is significant to support the biodegradable material claims. The biodegradability of PLA has become one of its major selling points in the 3D printing industry. However, this fact has become heavily challenged in recent times.

Theoretically, water should be able to dissolve PLA. However, breaking down a polymer like PLA to its monomers via hydrolysis is a prolonged process. At this point, the question becomes this – can water dissolve PLA within a reasonable time frame?

A lot of people have already done water solubility experiments with PLA. Two of these are particularly interesting:

  • Put one PLA print in a water cup at room temperature, and it is away from direct light for 3.5 years. PLA came out relatively unscathed, retaining good durability and close to its original color.
water-dissolve-PLA

Put PLA part in water 

  • Submerge several discs of PLA in a 70 °C water bath with continuous mixing. After seven days, all of the PLA discs ended up cracking or breaking apart. However, they were still solid.
Based on these results, it appears that temperature and circulation are critical components in dissolving PLA in water. Even then, it will take several days before the significant dissolution of PLA will happen. This experiment proves that water is unlikely the solvent for post-processing PLA prints or cleaning PLA residue.

Why Acetone Could Dissolve PLA

Now that we know water has limitations as a solvent for PLA let’s switch the discussion to acetone.

Acetone is an organic solvent and is considered one of the most critical solvents in households, industries, and laboratories. In 3D printing, acetone mainly uses to dissolve or smooth ABS.

1. Chemical Compatibility

Theoretically, acetone should be a compatible solvent for PLA. It bases on the fact that acetone is an organic solvent and that PLA is an organic polymer. The solubility of lactide (the monomers of PLA) in acetone has been relatively well-documented. It follows the “like dissolves like” rule of chemistry.

However, the real-world application of this concept is not that simple. When lactide monomers come together to form a PLA polymer, they become much more chemically stable. In this form, PLA is no longer as easily dissolvable by acetone. This stability becomes even more enhanced when PLA shifts from amorphous to a more crystalline structure.

Numerous 3D printing hobbyists have already tried dissolving PLA filament in acetone with no encouraging results. The result is often changing the PLA texture to something rubbery and splitting along the layers. There was no absolute dissolution, nor was there smoothing of the layer lines.

2. The Effect of Molecular Weight

chemical-structure
A promising study done by researchers back in 2013 explored the use of low molecular weight PLA as a delivery system for ovalbumin adsorption in vaccines. For this to work, nanoparticles made of PLA had to be manufactured via the solvent displacement method.

Using PLA with an average molecular weight of 9.3 kDa, the researchers could completely dissolve 50 mg of PLA in 10 mL of acetone. This experiment works because low molecular weight PLA polymers consist of shorter polymer chains. This structure makes them more available to chemical attack by solvents.

The problem is that most PLA resins sold in the market have relatively high molecular weight values. The numbers vary but are generally in the range of 50 and above. This type is ideal in 3D printing as it also gives the PLA filament enhanced strength and flexibility. However, if you can find a PLA filament with a low molar mass, that would be a good candidate for acetone dissolution.

Tips for Dissolving PLA

If you’re using acetone for dissolving PLA, then there will be specific safety measures that you will need to take. After all, acetone is still a solvent that volatilizes at room temperature and is flammable.

1. Safety

Assume that there are acetone fumes in the room and wear breathing and eye protection. You may also wear gloves when handling acetone, although the risk of skin absorption is low.

2.Ventilation

Exposure to acetone fumes becomes a problem if it happens regularly and at very high levels (about 1000 ppm or higher). To avoid an accumulation of acetone fumes, make sure to work in a room with good ventilation.

3. Time

Even with breathing protection, you should keep to the minimum time when exposed to acetone fumes. If you plan to submerge PLA in an acetone solution, make sure to place the container in a room that evacuates people and has good ventilation.

4. Flammability

Acetone is a highly flammable compound, whether in liquid or gas form. Make sure not to have any possible sources of ignition in the same room when working with acetone. Even an electrical spark could be a problem, so you may want to unplug any unnecessary devices.

Other Solvents That Can Dissolve PLA

1.Tetrahydrofuran (THF)

Tetrahydrofuran (THF) is one of few solvents compatible with PLA. Brushing it directly on the surface of a PLA print is quite effective in removing layer lines. You may need to do this several times to get good results.

THF is a powerful solvent and a highly toxic chemical. Handle it with extreme care. Wearing gloves, goggles, and breathing protection are very important.

2. Chloroform

Chloroform or dichloromethane mainly uses for vapor treatment of PLA.

Chloroform fumes are hazardous and could link to several types of cancer. Working with a fume hood is ideal, but you can also do this in a room with excellent ventilation.

3. Ethyl acetate

Ethyl acetate is a far safer and easier-to-obtain alternative to THF or chloroform. It is another option for the vapor bath treatment of PLA with mostly successful results.

Just like acetone, ethyl acetate fumes can cause respiratory irritation and nausea. It’s best to do the vapor bath treatment in a well-ventilated place.

4. Sodium hydroxide

Lastly, a solution of caustic soda or sodium hydroxide (NaOH) cites as being able to dissolve PLA completely. This material has a significant effect in dissolving PLA supports used in an ABS print. The very high pH in a caustic soda solution encourages the chemical reaction of PLA with NaOH.

As with the other compounds in this list, NaOH is a hazardous material that can irritate the skin, eyes, and respiratory system.

Summary

There is no clear consensus yet on which solvent is best for dissolving PLA. While acetone has potential, there are still other factors that need to be considered. These include the molecular weight of the PLA material and its degree of crystallinity.

Other solvents such as THF or ethyl acetate may be viable alternatives. However, these solvents are also quite hazardous are not as readily available as acetone. Make sure to work with the proper safety gear and practices if you plan on doing solvent treatment for PLA.