If I had it,, I would cut a tiny strip from one edge and hold it with tweezers in front of an iron set on high just to see what happens !! If it melts or anything similar,, you would know its probably 20th century !!
If you are close to a large city,, maybe take it to a museum and see if they have an idea !! Check out Mt Vernon Historical Society !! They may know what it is,, send pics if you can !!