Functional waterborne polymer dispersions for high performance anticorrosion coatings
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The design of thin and multifunctional waterborne latexes for anticorrosion application has been carried out in this thesis. Poly(MMA-co-BA) waterborne latex (MB) with phosphated functionalities (provided by using a polymerizable phosphate surfactant) was synthetized in order to trigger the formation of a passive thin iron phosphate layer at the metal-coating surface during its application. In fact it was found that phosphate waterborne latex was able to phosphatize the steel surface when cast onto low carbon steel and dried under slow drying rate (T=23 °C and RH= 60%) leading to excellent anticorrosion protection in harsh conditions of salt spray chamber. In an attempt to increase the barrier properties of this initial waterborne phosphate containing latex, the incorporation of high hydrophobic perfluorooctyl acrylate (POA) into the polymer composition was targeted. However, despite the enhanced hydrophobicity and the presence of iron phosphate layer at the coating-substrate interface, the coating cast from PMB was not able to protect the metal substrate against corrosion in the harsh conditions present in the salt spray chamber. In order to overcome the poor anticorrosive performance of POA nanohybrid latexes containing ZnO nanoparticles and phosphate functionalities was prepared. Unfortunately, the encapsulation of ZnO nanoparticles produced just a slight enhancement of the corrosion protection and these results indicate that the incorporation of ZnO nanoparticles is not enough to overcome the problem of the lack of coalescence of polymer particles observed for film cast from PMB latexes. The incorporation of hydrophobic Stearyl Acrylate into the latex composition was implemented as alternative and the synergic effect of enhanced barrier properties and substrate phosphatization allowed an enhancement of the corrosion protection with respect to the initial system based on MB. Finally, the incorporation of phosphated waterborne latexes (MB, SA40 and SA50) into commercial paint formulations for direct to metal (DTM) application provided paints with comparable anticorrosion properties to a commercial DMT paint but without the use of corrosion inhibitors.