Hello,
if "smooth polygons" causes issues, it's typically a problem of the mesh.
For sharp edges, the facets should link to separate vertices (even if they have the same
coordinates), to model a surface, there should be just one vertex.

Usually that problem can be fixed by exporting the object from the modeller with
certain options set / unset. (For blender: Use the object modifier "Edge Split", and check
the option "use modifiers" in the .obj export. If the default selection of "sharp edges" does
not work for you, you can set them explicitly (in blender))

Best regards,
   Michael