(167w) Role of the Polymer Molecular Structure and Surface Interactions on the Corrosion Resistance of Epoxy Coatings on Metals

Epoxy resins have long represented the gold standard of thermosets in terms of superior strength, excellent corrosion resistance, strong adhesion to substrates, and good thermal and chemical stability. These properties lead to their widespread use in applications such as adhesives, composites, coatings, encapsulating materials, and toughening additives. Nevertheless, these resins are facing increased scrutiny due to the hormone mimicking structure of their precursor, BPA, which is linked to several health risks. In order to come up with safer, equally performing resin candidates, one needs to understand the mechanisms of their superior corrosion protection as coatings. We will report a structure-property investigation of these mechanisms from epoxy resin molecular standpoint and the factors leading to macroscopic corrosion protection of the coating-metal system. We also examine the effect of the metal passivation treatment on the initiation and progression of coating degradation under accelerated acidic conditions. We combine optical, electrochemical, and thermomechanical approaches to reveal the key aspects contributing to the resistance and failure of the epoxy coatings. Our results show that that the coating molecular structure, even more than its adhesion to the metallic substrate, largely dictates how the coating swells, allows water and ions diffusion, and subsequently delaminates from the underlying substrate. A pivotal role in the initiation of “blistering” of the coating, which ultimately leads to coating breakdown, is placed on the elastic properties of the coating and its crosslinking density. Osmotic blistering is shown to be the main mechanism leading to coating failure in these coating-metal systems, due to buildup of corrosion products at the coating metal interface. The electrochemical processes at the interface, controlled by the metal surface composition, are interpreted via electrochemical impedance spectroscopy and energy dispersive X-ray analysis within the scope of coating corrosion resistance and degradation. These findings can be used as a fundamental guidance to tailor the formulation of the next generation safer resins which could match or exceed the excellent corrosion resistance properties of their epoxy counterparts.