The Waterborne Symposium 2025

Co-Author: James Rawlins

Abstract

The effective mitigation of corrosion through the application of protective coatings is of paramount importance, impacting both economic and safety outcomes.  Historically, the detection of coating failure and the ensuing corrosion has largely depended on visual inspection and destructive testing methods, which do not adequately predict onset or service lifetimes.  Current methods also lack correlation to specific polymer characteristics that govern corrosion resistance.  This research introduces a novel, nondestructive method that combines Electrochemical Frequency Modulation (EFM) and Confocal Laser Scanning Microscopy (CLSM).  By studying epoxy-amine coatings through a range of tailored glass transition temperatures (Tgs), ranging from high (269 °C) to sub-ambient (4 °C), these research results work contributes to the predictive modeling of coating lifetimes and advances our understanding of the relationship between polymer properties and performance in mitigating corrosion.
Previously, we have shown that the more hydrophilic a crosslinker was, the faster micro-blister formation around a predefined defect occurred.  Micro-blister with delay times varied from 47.5 to 5.5 hours for coatings with increasing hydrophilicity.¹  These results showed that a coating with a Dry Film Thickness (DFT) of 45 μm reduced micro-blistering and exhibited slower corrosion rates compared to the same materials at 5 μm DFT. These results emphasized the role of mechanical beam integrity and corrosion resistance and confirmed that coatings that limit swelling in water and delay physical state changes during immersion were dramatically better at reducing corrosion activity. Example, a coating designed with a high glass transition temperature (Tg) of 269 °C showed less than 3% swelling under all conditions and preserved mechanical properties, including a storage modulus of 2416 MPa, after exposure to corrosive environments. The results indicate that strengthening the mechanical robustness and reduced swelling and physical state changes (such as from glassy to rubbery) for a given coating during exposure are crucial for corrosion control and substrate protection.