Tips & Tricks: Dissolving U-HIPS in Limonene

If you’re a long-time 3D printing maker (or if you read our last Tips & Tricks blog post on using support material in your 3D printing), you’ve no doubt come across HIPS as a potential material that is good for printing support structures. Many makers who use HIPS as their support material will combine it with a non-dissolvable material like PLA or PETG, then use limonene to dissolve the HIPS as a post-processing step to get their final model. But one question that we’ve been asked a fair number of times is whether or not our U-HIPS filament can also dissolve in limonene. So we put our material to the test so that we could finally provide the proper answer to this question.


For this experiment, we used U-HIPS as the support material and hPLA as the model material.


Understanding Limonene

But before we get started, let’s briefly go over what limonene is and how it’s used to dissolve materials. To start off, limonene is a solvent made out of citrus oil. Commonly the HIPS is dissolved with D or R Limonene, in a bath agitated by an ultrasonic wand. This style of dissolving support allows for clean cutaways of the support material. The chemical is able to wear away the bond structures that give polystyrene its shape and crystallinity, effectively dissolving the material away. Limonene, however, has no effect on the polyamide structure of PLA, so it doesn’t cause any noticeable change in the model material’s crystalline structure. By submerging the print with both HIPS and PLA in a bath of pure limonene, the HIPS will dissolve, leaving the PLA intact.


Experiment

Now, let’s dive into the experiment.




Materials & Equipment:

Limonene

Water

Glass vessel capable of watertight seal

Gloves and goggles

Printed test specimens with U-HIPS and PLA and PETG


Procedure:

We conducted each test by printing the same print specimen using U-HIPS as the lower half and PLA as the upper half.

Two 3D printed specimens with brown PLA on top of party pink and black U-HIPS

Even though support material is typically printed with a lower density than the model material for ease of removal, we chose to print both parts with equal densities so that we could determine the maximum limit of time it would take to dissolve all of the U-HIPS.

After ensuring that the glass vessel is clean and dry and that a proper sealing lid is ready, we poured the limonene dilution into the vessel, enough to completely submerge the printed specimen. Remember to always wear the proper protective equipment, like gloves and goggles, when working with chemicals

We recorded the weight of the printed specimen, then cleaned the piece with rubbing alcohol and allowed it to fully dry.


Then we placed the cleaned specimen into the vessel so that it is fully submerged in the limonene dilution on its side, with the U-HIPS and PLA in the same plane. After securing the lid onto the vessel, we swirled the entire vessel to agitate the solution and the object.


3D printed specimen in PLA and U-HIPS placed in a jar with limonene solution

After the U-HIPS appeared to be completely dissolved, we removed the lid, and used tongs to remove the remaining object from the solution and allowed it to dry, recording the time elapsed as well as the weight of the object after completion.


3D printed specimen to the right of jar of limonene. The bottom half of the specimen is now completely dissolved


Results:

The following data table contains our findings for the time it took to dissolve the U-HIPS support material in relation to the concentration percentage of limonene in the dissolving solution.


Through this experiment, we were able to confirm that our U-HIPS filament does in fact dissolve in a similar fashion to its raw material counterpart. We were also able to confirm that U-HIPS filament is compatible with both PLA and PETG as a support material, which means that U-HIPS can make a great substitute for conventional HIPS filament, even when using it for support structures.


3D printed specimen using U-HIPS and PETG
3D printed specimen using U-HIPS as a support for PETG

On average it took around 1-1.5 hours to dissolve 1 gram of U-HIPS using the pure limonene solution. While intending to test different levels of limonene dilution, we found that limonene was immiscible in water, so limonene and water together would not form a homogenous solution, potentially requiring a different solute like alcohol or citric acid.

In future tests, we want to determine the rate of dissolution at dilutions of limonene rather than pure limonene to help determine the most cost effective formula for support material removal.


Another interesting observation that we made during our tests was that Nebula Black appeared to dissolve faster than Party Pink. This could be due to the addition of the carbon black powder we use to give Nebula Black its color, but this is something we have yet to confirm.


As far as disposal goes, by allowing the effluent limonene to simply disassociate in an open metal container (such as a baking pan) the need for liquid hazardous waste removal is effectively eliminated, leaving only a solid plastic byproduct behind.


Limonene solution byproduct

Well there you have it folks, the question of "but can it dissolve?" is now answered!

So the next time you're looking for a supporting, dissolvable, and sustainable 3D printing material, be sure to grab some U-HIPS filament!

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