Physicochemical and structural effects of electrolyte‐induced delamination on polyethylene teraphthalate‐coated steel plates

Abstract

This research evaluated the in situ physicochemical changes and alterations occurring in an electrolytic chromium coated steel (ECCS), surface protected by polyethylene teraphthalate (PET) copolymer, after inducing a fracture on the coating in an acid acetic-acetate medium. The delamination was characterized in the front of the failure by means of anodic and cathodic electrochemical mechanisms, and the resistance and degradation of the metal-polymer composite's substrates were analyzed by means of Raman vibrational spectroscopy. The application of an electrochemical cell to generate in situ delamination, simulating the formation of pores or artificial defects, provided information on the activity inside the substrates of the PET-coated ECCS composite as a result of the effect of the acetic acid. The anodic delamination mechanism is based on the diffusion of the electrolyte through the metal-polymer interface and the pre-existence of pores on the polymer layer. The cathodic delamination mechanism is based on the mechanical action of the gaseous hydrogen as a result of the reduction of H þ .

Characterisation of nanometric chromium coatings in metal–polymer composites

“…Hence, the metallic chromium layer requires a minimum thickness in order to completely cover the steel, which depends on the deformation level of the material, to avoid failures and formation defects during manufacture. 12 In practice, the lack of continuity of the layers (Cr 0 and Cr 2 O 3 ) at certain points 10 facilitates delamination of the PET polymer protective coating and prevents chemical bonding. Thus, the design and manufacturing controls are highly important in metalpolymer materials employed in applications subject to deformations.…”

“…3), before the mechanical experiments were conducted, and showed variations preventing homogeneous deformations of the material. The literature reports that maximum polymer elongations are in the order of 10%9, 10 under thickness discontinuities. Figure 3 shows that the minimum and maximum thicknesses encountered for the PET polymer were 64·7 and 70·8 μm, respectively, with an average 68 μm.…”

Degradation of metal–polymer composite submitted to uniaxial deformations in 3.5% NaCl solution

“…However, the originality of the present study was to experimentally demonstrate that not always there is a linear effect resulting from uniaxial deformations and much less in a saline medium; it has been significant only for the 25% deformation strain. The changes in the potential and net charge transferred demonstrated variable behaviours for the 5-25% deformation range (Figures 4 and 5), due to the microstructural complexity of the composite, and the anodic and cathodic mechanisms involved [13,14]. That is, the deformations mainly affected areas of the chromium layers on steel; an assumption made because of the observable marks on the PET polymer caused by the morphological changes of the layers; it is evident that such layers crack and fracture (Figures 8, 10 and 11) in thin sheets under very aggressive environments (3.5% NaCl) and show discontinuities in certain areas, allowing low-deformation changes to exhibit increased activity in the layers.…”

“…The axially deformed samples (5-25%) were electrochemically tested and characterised; when observing their morphological changes (especially at extreme deformation), they showed evidences of degradation in the electrolytic chromium and PET polymer layers by the electrochemical activity of the saline solution [13,14].…”