None of the ref images are working for me for some reason, so I can't see exactly what it is supposed to look like, but I'll try to offer some advice anyway.
Instead of trying to glue the blade directly onto the staff, I would recommend cutting a slit into the pvc pipe to slide the blade into. That way it isn't able to just pop off if it gets hit against something on accident. Also, one of the strongest glue I know of is Gorilla Glue. It bonds pretty much anything to anything, but be careful and use it sparingly because it expands.