[Alx0101]

Hello everyone,

I cast jewelry as a hobby using the lost wax process. I use a resin material to 3-D print the models of my rings. The rings are created with a base or stand that is not part of the design so I dissolve that base material using an isopropyl alcohol bath. However after repeat usage, eventually my isopropanol bath becomes saturated with the dissolved resin material and I would need to replace the isopropyl.

So I was wondering if there is something I could measure to determine if the isopropyl is oversaturated? I was thinking about measuring the pH but maybe that isn't the correct property that I am looking for. Any and all suggestions are welcome.

Thanks,
Alx0101

[chenbeier]

Resin is organic material, a pH measurement makes no sense.Maybe mesure absorbance if the alcohol get change in colour. But IPA is cheap why not use every time fresh alcohol for cleaning.

[wildfyr]

Weight some out, let it sit in an open cup or gently heat it, and see what solid is left over after evaporationr. You need to determine for yourself at what level of solids you need to replace the isopropanol.

[Borek]

First of all: pH is a property of water solutions, you can't measure pH of IPA.

[Enthalpy]

The viscosity of the solution would tell how much of viscous resin is dissolved in the thin alcohol.

While evaporating the alcohol and observe the residue is a more direct and quantitative method, viscosity is faster and wastes no alcohol. In both cases, one must determine how much dissolved resin is acceptable to the use.

The measurement lets flow the liquid through a funnel and measure the time it takes. The small diameter must be chosen so that the liquid takes around 10s or more to flow through. Or better, compute the Reynolds number blah blah blah.

For accuracy, the exit of the funnel must touch the liquid at the downstream container.

[Enthalpy]

Why not recycle the alcohol before each use?

By distillation, you leave a little bit of alcohol behind containing concentrated resin, and the alcohol obtained after condensation is knowingly pure and ready to use. No measurement needed.

Beware this is badly dangerous. I nearly killed myself with a similar game. Better do it outside.

And be vigilant during the distillation, as too concentrated resin in the retort over the heat source would decompose and possibly leave a stinky compound difficult to remove.

By the way, isopropyl alcohol is a big fire hazard even at room temperature. I hope you have already thought through, prepared and trained how to extinguish its fire (no water!) and leave the room. Be paranoid: things do go wrong.

[Enthalpy]

I didn't expect isopropyl alcohol would dissolve the resin. It's my usual choice to clean a plastic part without dissolving it. Acetone dissolves polymers like ABS far better.

[Enthalpy]

The proper method industrially would dissolve the resin using solvent vapour. Very much like dry cleaning of clothes: boil the solvent, let it condensate on the part to dissolve. This brings clean solvent on the part and leaves the dissolved resin in the liquid. If you prefer, it's dissolving and recycling the solvent in one step.

Though, I feel it far too dangerous at home. If the vessel is closed, boom due to overpressure. If it's open, boom due to air+vapour mix. It would need a non-flammable solvent, but most are banned now for being carcinogenic. It also needs a special design with several stages of varied temperatures and compounds.