Influence of TiO2 pigment particles on chromate ion transport in epoxy films

Transport of active species (i.e., ions) leaching from pigment particles incorporated in a polymer matrix is the main mechanism behind the anticorrosive performance of protective coatings. Understanding this mechanism is necessary for the effective design of the systems utilizing pigments less toxic than the most efficient chromate salts. It was demonstrated that anticorrosive pigment particles can themselves facilitate the transport of active species via the pathways formed after pigment leaching from a coating. It was also suggested that other paint components, e.g., certain additives, pigments, and fillers can be involved in the formation of transport pathways. Investigation of the possible influence of inert pigment (TiO2) on creating the pathways for chromate ion transport in polymer coatings was the primary objective of this work. In an experiment mimicking the transport of pigment species (i.e., chromate ions), a model epoxy coating containing particles of a single pigment (TiO2) was exposed to a chromate solution (aqueous, or with the addition of acetone as a polymer swelling agent). It was shown that the chromate ions can be transported in the epoxy film preferentially via the TiO2 particles/polymer matrix interface.