Dissolving PLA used as support for ABS prints

Success: I tested with an ultrasonic cleaner and laboratory grade Sodium Hydroxide @ 60°C and got a surprise result:
[www.vinland.com]
Bertho

Very interesting ! I have a dual extruder project and I want to use it to print soluble support structures. I planed to do the same experiments once my dual extruder is functional.
Does the ultrasonic pulses makes a lot of differences or a heated bath of sodium hydroxide is enough to dissolve the PLA ?
Is the sodium hydroxide has to be laboratory grade ?

I expect that the ultrasonic cleaner will make a big difference.
The grade is not important. I happened to have it available and I wanted to know accurately what was used for the testing. Sometimes store cleaners are mixtures but I do not think it is critical.

This is how 3D Systems does it, right?

[www.youtube.com]

Ultrasonic + Caustic Soda for 3 hours....

That is exactly what I wrote and I included the link to that video.

Can you try with the heater on but the ultrasonic switched off ?
If it works too, (it will certainely takes longer) we can build a dirt cheap support removal device by modifying a kitchen appliance.

I initially heated samples in my first set of tests but not for a long time. Afterwards I left the samples in the solution for several weeks but there was not a significant change in appearance. So in summary, it looks like ultrasonic is needed.

Maybe if it was at boiling temperature but that adds significant risks and also possibly warping the desired object from the heat.
Bertho

Are ultrasonic cleaners that hard to make? these instructions seem easy enough:

[deiwhy.blogspot.ca]

It sounds reasonable but audio power amps are not made to continuously operate at those frequencies and can easily overheat. There is no mentioning of tuning the system so it will be resonant. Many ultrasonic generators required a counter weight mounted to the other side of the transducer to operate efficiently. Plus you must have the unit tied to a PC if you do not design a separate signal generator.
So in summary, more work than it sounds like in the simplified description.
By the way, I have designed several commercial ultrasonic products that were marketed years ago.

Small ultrasonic cleaners does not have a heater function and the timer is very short. The smallest ultrasonic cleaner with heater function cleaner I found (Velleman VTUSCT5) has a capacity of 2l but the timer's maximum is 30min only. I don't have the space or the usefulness for a bigger one.
It seems the ultrasonic pulses are mandatory, so I think I will need to buy this 2l cleaner and hack it to increase the timer maximum, but it is clearly stated on the manual that this cleaner is not made to run continuously.

Eventually, I made an hot plate/stirrer :
The cardboard case is temporary, I will make a wiki about it once finished.

The PLA support is dissolved in 6H30 (heating-up included) with 100g of sodium hydroxide dissolved in 500ml of water at 60°C.
I also put other filament in the bath :

From top to bottom :
-Test part (GRRF white PLA / black ABS)
-GRRF white PLA
-orbi-tech transparent PLA
-GRRF transparent blue PLA
-GRRF soft PLA
-GRRF LAYWOOD

The soft PLA isn't affected so much and LAYWOOD isn't affected at all by the sodium hydroxide, so we can make rubbery or wood-like complex parts using PLA as support
For the next test, I will increase the temperature to 80°C to speed-up the process.

Thank you for the update.
It will be a nice finished product.

At 80°C, the support is dissolved in 3Hrs
And I lowered the concentration to 50g / 500ml

Edited 1 time(s). Last edit at 04/15/2013 05:27PM by Petrus.

This is sweet. I just happend to have a large heated ultrasonic cleaner. Now I don't need to buy PVA as support - as that is more than twice the price of PLA.