Do I need any kind of separator / release agent when casting concrete in shuttering plywood forms?
I've seen this done with melamine-coated boards. I would make sure that the plastic veneer of the boards you're using is one solid piece. Family Handyman indicates you don't need any special chemicals to get it out of the form


  To remove the form, pry off the long sides and then the short sides. Pry against the form base rather than the concrete. If you have to pry off the form base, use a plastic putty knife; metal will mar the surface