I kept the empty containers of IPA with the expectation of emptying the FormWash and then taking them to the dump for disposal. But I was busy and the containers just sat around for awhile after I used the siphon that comes with the FormLabs to refill them.
I noticed that the resin sank to the bottom of the containers and I could just put the top-most level of each container back into the FormWash. Not perfect but it means I’m using a lot less IPA than expected.
I suspect that if I actually clean the inside of the FormWash out instead of just stopping when the siphon isn’t bring much IPA out I’ll get even more use out of the IPA.
A solution of Alum in water is used to catch the resin and make it sink to the bottom. This works quite well. Unfortunately at the same time you dilute the IPA with some water. I tried pouring the Alum directly into IPA, but it didn’t want to dissolve. My used up IPA now washes better, but not nearly as good as fresh IPA. I used for a kind of pre-wash now.
The resin settles out very quickly, 48 hours or so it all it takes for the completely opaque IPA in my first-wash bucket to become completely clear with a thin layer of “powder” at the bottom. That “powder” is what the bottom of a wine bottle (“punt”) is designed to capture, too. Pour off the clear liquid and when the resin material starts to flow over the edge, stop pouring and dispose of the little bit remaining that’s now nearly 100% resin.
I just submerge filter cone in the IPA bucket and after 48 hours I remove the filter with maybe 80% of the resin coming out with it. What’s left isn’t crystal clear, but it doesn’t need to be.
Let’s just remind people (again) why resin and IPA can’t be separated without distilling.
Uncured resin is a mixture with four main constituents:
1/ a Monomer
2/ a Linker
3/ Liquid fillers
4/ Pigments and solid fillers
In the presence of UV light, the first three of these react together to form a solid. When liquid resin is mixed with IPA these three liquids will dissolve and, if allowed to settle, the pigments will fall out of suspension.
If there is a strong solution of resin in IPA then the molecules of the three liquid constituents will be close enough to each other so that UV light will trigger a reaction and the whole solution will form a solid gell. On the other hand in a weak solution, the molecules will be far enough apart not to be able to react and the solution will appear to be similar to pure IPA, though the specific gravity will be higher.
All this is part of the basic thermodynamics that rules the Universe, a high entropy mixture cannot be separated without the addition of energy. In this case, the energy is the heat needed for distillation.
Well, i would say it works to some degree:
I made a mixture of IPA with 10 wt% resin and exposed it to uv light. A syringe and steel wool was used as a filter.
The 6.88 g of mixture separated into 6.25 g filtered liquid and 0.44 g filter residue. That doesn’t look so bad (64 % reduction). But the dry weight of the filter residue is only 0.17 g (25 % reduction).
