Environmentally friendly hybrid coatings for corrosion protection: silane based pre-treatments and nanostructured waterborne coatings

This thesis considers a nanotechnology approach based on the production of metals pre-treatments and organic coatings (a complete protection system at all) designed from the nanoscale. The final aim is to develop protection systems with improved corrosion protection properties and a low environmental impact. In particular, multifunctional silane hybrid molecules were used to design sol-gel pre-treatments for metals and to modify the inner structure of UV curable waterborne organic coatings. In the first part of this thesis thin (hundreds of nanometers) sol-gel films consisting of an experimental mixture of hybrid silicon alkoxides molecules were applied onto aluminium and hot dip galvanized (HDG) steel for the development of effective and environmentally friendly corrosion protection systems A chemical and electrochemical characterization of the sol-gel films highlighted their good corrosion protection properties both for aluminium and HDG steel. To test the effectiveness of the sol-gel coatings as coupling agent between metallic substrates and organic coatings (paints) both a powder coating paint and a cataphoretic coating paint were applied on the silane pre-treated substrates. The electrochemical measurements and the accelerated tests carried out on these protection systems proved the capability of these sol-gel conversion coatings to improve the corrosion protection properties of the traditional protective cycles. The performance of the silane pre-treatments was also compared to commonly used surface conversion coatings for metals. The result of this comparison evidenced that the corrosion protection properties ensured by the sol-gel conversion treatment is comparable or higher than most of the commonly used pretreatments. A study about the incorporation of inorganic nanoparticles into these sol-gel films gave evidences of an improved corrosion resistance due to the addition of certain amount of montmorillonite nanoparticles in the sol-gel matrix. The same hybrid silicon alkoxide molecules used to perform the pre-treatments were used modify the inner structure of UV curable waterborne coatings in order to improve the corrosion protection properties maintaining the environmental compatibility of the protecting system. The design, application and characterisation of urethane, acrylic and epoxy waterborne UV curing coatings modified with the hybrid silicon molecules in order to obtain nanostructured waterborne films with improved corrosion resistance and thermomechanical properties were studied. The characterization proved the great potential of the silicon alkoxide molecules as a tool to modify the properties of the organic matrix of the paint: silicon alkoxides can promote the self assembly of inorganic nanoparticles into the matrix or can act as an effective coupling agent between inorganic nanoparticles and the polymeric matrix. Silicon alkoxide molecules were proved to be an efficient tool to design a protection system from the nanoscale leading to the prospective of an accurate control of the overall properties of the macroscopic systems.