Polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) as additives of organic coatings to prevent corrosion

The aim of this work is to compare the protection against corrosion imparted by different conducting polymers when these materials are used as anticorrosive additives in the formulation of conventional epoxy paints. Specifically, the polymers employed as anticorrosive additives are polyaniline emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with carbon black, polypyrrole composite with carbon black and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate). Initially, the structural, thermal and mechanical properties of the unmodified epoxy paint as well as the modified coatings, obtained by the addition of 0.3 wt.% of conducting polymers, have been characterized. After this, controlled accelerated corrosion assays in an aggressive solution medium were developed using coated steel panels. Results indicate that the protection against corrosion imparted by the formulations modified by the addition of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate), polyaniline emeraldine salt and, especially, polyaniline emeraldine base is significantly higher than that of the unmodified paint. In contrast, the use of conducting polymer composite with carbon black reduces the efficacy of the coating. Results indicate that some conducting polymer compositions should be considered as a suitable alternative to replace inorganic anticorrosive pigments currently used in paint formulations.