Dr. Barry Ornitz wrote about this in several groups about twenty years ago.  Do a search on "Barry Ornitz radio plastic" and the same with "radio plasticiser" and you will get quite a few hits on his methodology.  And of course he had the lab at Kodak to do material analysis.  His conclusion was that you can't put the genie back in the bottle.  The closest I've come without resorting to etched brass material has been by using a a TLC 5500T credit card lamination machine with a 15 Mil thickness credit card "pouch".  I had to get a better machine to do it well - the first one I bought didn't get the thicker 15 Mil credit card material hot enough. Below is one of the results, this for a WWII pulse analyzer.  (The original is on top...)



73,
Mike  KC4TOS