Forensic characterization and discrimination of automotive Vinyl wraps using ATR-FTIR and Raman spectroscopy with chemometric classification

Automotive vinyl wraps are an increasingly more common vehicle surface material that may be encountered as trace evidence in investigations. Despite their growing prevalence, no framework for the examination of vinyl wrap materials by vibrational spectroscopy has been established. This study used attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and Raman spectroscopy in combination with partial least squares discriminant analysis (PLS-DA) to classify automotive vinyl wrap samples. Vinyl backing and adhesive layers were examined from commercial vinyl wrap samples representing various manufacturers, colors, and surface finishes. Principal component analysis demonstrated complete inter-class separation for ATR-FTIR backing spectra while Raman spectroscopy provided complementary discrimination driven primarily by inorganic pigment composition. PLS-DA roll level classification models achieved overall accuracies of 77%, 73%, 70%, and 45% for the ATR-FTIR adhesive, ATR-FTIR backing, Raman backing, and Raman adhesive models, respectively. Misclassifications were predominantly confined to within-class roll-level confusions rather than between product classes. Sequential examination of all four confusion matrices revealed that the combined analytical workflow reduced the number of indistinguishable sample pairs to a single within-class misclassification.