You can identify plastic by setting fire to it, making observations of flame colour and smell, etc, and then consulting a chart like this: http://www.boedeker.com/burntest.htm. Best to do it outside of course.
There are machines that can do this, but they are very expensive.
They are handheld X-ray fluorescence devices “xrf guns” and they cost a few grand, but they can give you a detailed breakdown of the elements in something without destroying it. Or using fire.
Ha, you had me freaking out there for a minute.
I really want an xref gun, but they cost $$$$$
That links is selling a service where you send your sample to them, they scan it and send it back.
For little things that might be fine, but for big chunks of metal, not so much.