If by chance you mean Coroplast, flash and CA is the least obtrusive way to go. In lieu of the torch, a good scrubbing with mineral spirits and a Brillo pad will also remove the manufacturing residue.

The problem is not with the adhesive, but with the fact that there is a thin film of oil/grease on all surfaces of the Coroplast. Once that film is gone, you can use Goop, CA, contact cement, even polyurethane glue to stick it together.