Polyethylene terephthalate (PET) is a polymer coating that protects the electrolytic chromium coated steel (ECCS) against aggressive electrolytes like NaCl. It is widely accepted by manufacturers that NaCl has no effect on the PET coating, which is inert. However, we showed that there are some effects at the structural level, caused by vibrations, and facilitated by defects on the layers. The vibrations occurring during the transportation of food containers produce delaminations at given points of the metal-polymer interface, known as antinodes, which in turn may produce PET degradation affecting food quality. The former can be determined by electrochemical measurements, and the changes in composition or structural order can be characterized by Raman. The present work applied this latter technique in experimental samples of PET-coated ECCS sheets by performing perpendicular and parallel analyses to the surface, and determined that it constitutes a new potential methodology to determine the behavior of the composite under the above conditions. The results demonstrated that the delamination areas on the PET facilitated polymer degradation by the electrolyte. Moreover, the Raman characterization evidenced the presence of multilayers and crystalline orderings, which limited its functionality as a protective coating.

This research evaluated the degradation performance of metal-polymer laminates. The material employed was an electrolytic chromium-coated steel (ECCS) sheet, protected by polyethylene teraphthalate (PET). This composite was submitted to uniaxial deformations simulating those occurring in the formation of containers. Later, it was electrochemically tested in 3.5% NaCl w/v solution and characterised by scanning electron microscope (SEM). Finally, an evaluation of the degradation activity was made to determine the potential performance of the composite in canning applications. The results indicated that the deformation-degradation correlations of the layers depended on the plastic deformation, strain energy, surface quality of the PET polymer free from defects (with respect to a control sample), lack of continuity of the chromium oxide layer at the interface level due to the generation of microcracks, grain deformation in the metallic layers -both of ECCS and chromium layer -due to the generation of Lüder's bands, loss of adherence detected by electrochemical tests and surface morphological changes of the protective polymer by uniaxial deformations.