i would fill em with alcohol one by one swish em around until you have absorbed your goodies. transfer to the next bag and repeat. drip the bags empty into a bowl or something and then toss the bags out.
Sandwich bags were not designed the same use as the volcano bags were (designed to be safe for food uses under oven like temperatures.) Sandwich bags used under normal everyday uses? Probably totally safe to use. to use in your cooking process to remove the actives? I wonder...
When cheap plastics are heated they will give off tiny bits of plastic into your solution in this case the edibles! I don`t think that is a good idea!
Just beware if you do that.
another safe method would be to take a nice big glass surface and lay it down on a table. then beat the hell out of your bags, I would turn em inside out, and put them on like gloves and then clap rubs etc... then just scrape up your collected powder off the glass
you might be surprised with the return