Effects of surface roughness, texture and polymer degradation on cathodic delamination of epoxy coated steel samples

The Scanning Kelvin Probe (SKP) technique was used to investigate the effects of surface roughness, texture and polymer degradation on cathodic delamination of epoxy coated steel. The cathodic delamination rate of the epoxy coatings dramatically decreased with increased surface roughness of the underlying steel substrate. The surface texture of the steel substrates also had a significant effect in that samples with parallel abrasion lines exhibiting faster cathodic delamination in the direction of the lines compared to the direction perpendicular to the lines. The cathodic delamination kinetics of epoxy coatings previously exposed to weathering conditions increased with prolonged exposure due to pronounced polymer degradation. SEM observation confirmed that the cyclic exposure to UV radiation and water condensation caused severe deterioration in the polymer structures with surface cracking and erosion. The SKP results clearly showed that the cathodic delamination of the epoxy coatings was significantly influenced by the surface features of the underlying steel substrates and the degradation of the coatings.

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► Cathodic delamination of epoxy coated steel samples was studied using SKP.
► Delamination of the coating decreased with increased substrate surface roughness.
► Delamination of the coating was faster on the substrate with parallel surface scratches.
► Delamination of the coating exposed to weathering conditions increased with prolonged exposure.