Contribution of Polarized Raman Spectroscopy Imaging and Chemometrics for the Analysis of Residual Scratches on Polyethylene Terephthalate Surfaces

Abstract

Scratch testing of polymer surfaces generates complex local stress and strain fields that strongly influence molecular organization, yet the underlying mechanisms remain difficult to resolve experimentally. Understanding these processes is essential for predicting surface damage and improving material durability. In this study, the molecular response of amorphous PET subjected to plastic scratch deformation is examined by combining mechanical scratching with postmortem polarized confocal Raman microspectroscopy. This approach enables spatially resolved chemical and structural characterization of the deformed and undeformed regions. Multivariate chemometric analyses are used to extract subtle spectral variations, providing a more comprehensive interpretation than classical band-intensity univariate methods. Using this methodology, the polarization configuration most sensitive to deformation-induced structural changes is at first identified. Then, high-resolution postmortem Raman mapping reveals specific Raman bands whose intensities correlate with local scratch-induced strains, indicating chain orientation and the formation of an orientation-induced mesophase during scratch. These findings provide insights into the microscopic mechanisms governing polymer reorganization under concentrated mechanical loading. Beyond PET, this combined mechanical-spectroscopic framework offers a robust approach for characterizing deformation and damage processes in a wide range of polymers. It also establishes a foundation for future studies, including environmental effects such as temperature and humidity, and for progressively moving toward an in situ coupling of the two experimental techniques.