Water-based & eco-friendly epoxy-silane hybrid coating for enhanced corrosion protection & adhesion on galvanized steel

Abstract

Abstract In this current study, epoxy-silane hybrid coatings were designed to investigate their anti-corrosion performance and adhesion on galvanized steel. Silanes with alkoxy group, epoxy group, amine group and thiol group were chosen to understand the role of functionalities in the performance of designed hybrid coatings. Moreover, the silanes were added at three different concentrations into epoxy polymer to asses the effect of concentration on anti-corrosion and adhesion properties of the coating films. From scanning electron microscopic (SEM) images, we observed a uniform coating without any agglomeration of coating particles over galvanized steel substrates. The corrosion performance of casted and cured films was evaluated by using potentiodynamic polarization and AC impedance spectroscopy method. The physical properties, such as, thermal behavior and thermo-mechanical behavior were studied using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) respectively. The adhesion strength between coating films and galvanized steel substrate was checked by ‘pull off’ adhesion test. It was found that due to the grafting of sol-gel coatings onto organic polymer backbone, the adhesion property and anti-corrosive performance has improved remarkably as compared to non-grafted epoxy polymer. It was observed that amino silane showed superior performance compared to thiol silane. The poor performance of thiol silane grafted epoxy coating could be attributed to some chemical incompatibility of hydrophobic and non-polar sulfur silane moiety and hydrophilic and polar waterborne epoxy polymer backbone. Addition of silane by 1 wt% and 3 wt% into epoxy polymer backbone caused improvement in both anti corrosive property and adhesion strength but further increase of the silane concentration to 5 wt% led to deterioration of protective property of the films. This drop in performance can be attributed to excessive consumption of epoxide groups in epoxy resin by amino and thiol functionalities present in silane.