I think??? I remember reading someplace to never mix epoxy in a container in which food was stored. I have a bunch of the plastic cups that yogurt came in. The ''good'' kind not affected by solvents, at least not acetone or lacquer thinner. All have been thoroughly washed in hot soapy water. Before I ruin a batch of epoxy (glassing a whole airplane)..... Use them or not?
I use clean yogurt cups all the time they work great, and when the adhesive hardens its easy to pop the hardened material out,I get about 4-5 mixes out of one cup before it gets a bit beat up and then I get a new one.
having 2 young boys gives me a endless supply of cups to use for various uses mixing epoxy,paint,I even use them for sorting screws there handy.
so yes there fine to use for mixing epoxy