Recycling IPA

I use IPA (iso-propyl alohol)to wash models after printing; this removes resin stuck to the surface, and is vital if you want to get good resolution.

Part of the action is physical - it is just washing off the excess - but put of it is that the IPA dissolves the resin. There comes a point where the IPA is saturated, and it will not dissolve any more resin. And they will happen at different times with the different components in the resin.

So at this point you need to use fresh IPA, or to somehow renew the old.

Note that letting it stand so the resin settles out and then decanting off will not work. It will only remove resin that is not dissolved; if the IPA is saturated with resin, it will remain so.

Some people distil the IPA, and this is the only way to get high quality IPA back again. However, IPA is flammable, and when you distil you will necessarily be heating it beyond its flash point. If you buy equipment designed for distilling water there is no reason to suppose it was built for flammable solvents. I am not prepared to risk a fire.

The alternative is to expose the IPA to UV light. This will cause the resin to react, to form polymer, which is insoluble, and will crash out of solution.

To this end, I have a plastic container made of clear plastic, and quite tall. I pour in the IPA, put the lid on, and leave it out in the sun. Every half an hour of so I give it a shake. If the weather is poor, leaving it out for four to five days seems to work too.

The polymer that forms is kind of like cotton wool, and you should give the container a good shake to break up the polymer, then let it stand overnight. You can the decant off the top layer of IPA, where it is clear, and filter into a suitable bottle. Give the container another good shake - a really good one this time   and allow to stand for a few days, before decanting off again.

You want to be filtering IPA that is already more-or-less free of solid as the solid will quickly blind the filter, and stop the IPA passing through it. In fact, you could probably get away with not filtering at all if you are careful when decanting.

Whatever is left in the container is virtually all reacted resin. Tip it out and leave for a while to let the IPA evaporate, then just throw away. The container will have a coating of polymer, which you can scrap out to some degree, but does not seem to matter too much.

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