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Organic coatings are the single most widely applied materials to protect metallic substrates against corrosion. Therefore it is important to understand how a coating can guarantee the protective performance during service life. In this study it is tried to find how viscoelastic properties can affect the protective performance of a coating. An epoxy resin (Araldite GY 783) was cured with a mixture of two types of hardeners (a polyether polyamine and a cycloaliphatic polyamine) in four different mixing ratios (i.e. 20–80, 50–50, 70–30, 90–10) to achieve various adhesion behaviors, water permeability and viscoelastic properties. Samples were exposed to humidity in testing chamber for 300 days and adhesion was measured at wet and dry conditions over time. After drying, adhesion loss and recovery were evaluated by pull-off test. Electrochemical behavior of coatings was studied by electrochemical impedance spectroscopy (EIS). A series of impedance spectra of coatings during exposure to humidity were recorded and their protective properties were compared. The results showed a correlation between protective properties and viscoelastic behavior of coatings. It was found that a sample with higher percentage of cycloaliphatic hardener has higher elastic modulus (1275 MPa) and a sample with higher percentage of polyether poly amine hardener has the lower elastic modulus (465 MPa). Additionally It was found that a sample with excellent initial protective properties (|Z| = 10 10 Ω cm 2 ), higher elastic modulus and low initial water permeability (0.308 g/m 2 hr) may quickly fail because of the adhesion failure after wet cycles. [ABSTRACT FROM AUTHOR]

Two different approaches were used to modify a UV-curing resin based on polyester chemistry, namely molecular and nano-particular approaches. In the molecular approach a hydrophobic compound, glycidyl neodecanoate, was reacted with the resin and was fixed on the polymer backbone. In the nano-particular approach a nano-clay was used to modify the resin in a physical manner. The electrochemical properties of the coating films were investigated using electrochemical impedance spectroscopy. In all cases a broadening of the complex plane graph in the direction of real impedance axis was observed. It was necessary in all cases to incorporate a finite length warburg element into the equivalent circuit to account for this broadening effect. The presence of this element was attributed to an intermediate case of anomalous diffusion of charge carriers through the dense polymeric network of the UV-cured films. EIS investigations of the UV-cured films show that both molecular and nano-particular modifications cause the electrochemical properties of the film to remain constant for a longer immersion time compared to unmodified resin. [ABSTRACT FROM AUTHOR]

Highlights: [•] First time codeposition of a nano ZnO and a cathodic electropaint. [•] First time report on nano ZnO as an additives in cathodic electropaint for enhancing the corrosion resistance of coating. [•] Using EIS technique to evaluate the effect of presence of nano ZnO particles in the cathodic electropaint. [Copyright &y& Elsevier]