Influence of aqueous sodium chloride solutions on operational properties of epoxy coatings

The main goal of the research presented in the article is to assess the impact of the destruction (degradation) of epoxy coatings, caused by the influence of a 25% aqueous solution of sodium chloride (brine), on the operational properties that determine the coatings reliability (durability). Samples of two-layer epoxy coatings (obtained from powder paints) were aged by immersing them in brine for a maximum period of 1680 h. The following criteria were used to assess the operational properties of the coatings: thickness, roughness and surface morphology, hardness, water absorption (mass increase), surface free energy. The FTIR and DSC tests performed showed a progressive development of the oxidation processes of the epoxy with the ageing period. The long-term impact of the brine resulted in the destruction of the coatings in the form of: craters, grooves, microcracks, including silver cracks. The contact of the coatings with brine also increased their: surface roughness (Ra, Rz, Rmax), thickness, mass, surface free energy, and decreased hardness and heat resistance.