Hi David,
Infrared spectroscopy, specifically attenuated total reflectance (FTIR-ATR), should allow for qualitative identification of bulk polymer components in the liner or could differentiate the liner type. Back when I was in pharma, I used Chemir or Evans Analytical (both now bought up by Eurofins) or sometimes Jordi Labs for projects like this if I didn't have the time to do them myself. This should be a pretty straightforward project for a surface analysis lab that works in pharma or food/bev.
Not an endorsement, per se, but some details here FTIR (Fourier Transform Infrared Spectroscopy) Laboratory Services (eag.com)
Caveat: it's been over a decade since I did this kind of work myself.
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Jeff Muston
Technical Services Manager
Sierra Nevada Brewing Company
Mills River NC
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