RIASSUNTO
ABSTRACT
In the coatings industry, the development of a durable water repellent / superhydrophobic coating is of high interest to provide greater protection from water/moisture, therefore reducing steel corrosion especially for offshore applications. This study reports the performance of a volumetric water repellent topcoat and a two coat system composed of the water repellent topcoat on the top of an epoxy zinc primer. The anti-corrosive performance of the water repellent coating was evaluated by salt spray tests and the volumetric superhydrophobic effect by contact angle analyses. The preliminary results show a significant improvement on the anticorrosive properties compared to a standard coating material. The two coat system was evaluated up to 6000 hours in salt spray test; 7200 hours in blister box and sea water immersion test, and up to 10080 hours in ageing resistance test. The thermal crack resistance and flexibility of the system were also tested. The two coat system has shown excellent anti-corrosive properties for extended times of exposure and outstanding mechanical performance, making it a suitable candidate for areas exposed to aggressive environments such as offshore platforms.
INTRODUCTION
The interest in superhydrophobic or water repellent coatings has increased during the last years, driven by the potential industrial applications of these surfaces in different areas. Several techniques have been employed to create superhydrophobic coatings, and the majority rely on the generation of a coating surface profile or chemically modifying the coating's surface.1-4 However, when these surfaces are damaged, the superhydrophobicity is usually lost and consequently their inherent water repellent properties. Therefore, a volumetric superhydrophobic / water repellent coating could represent a breakthrough technology in the coatings industry.
In this paper, the performance of a volumetric water repellent polyurethane coating is evaluated. The volumetric water repellency was studied by contact angle analyses. Salt spray tests were performed to compare the corrosion resistance of the water repellent polyurethane coating and the corresponding standard. The performance of a two coat system composed of an epoxy zinc-rich primer and the water repellent topcoat was evaluated in terms of anti-corrosive and mechanical performance. The test methods used in this work make part of the most common standards to qualify a coating system for an offshore application. These include salt spray test, blister box test, sea water immersion test, ageing resistance test, flexibility, impact and crack resistance. The two coat system was evaluated for normal and extended times of exposure. The two coat system has shown excellent anti-corrosive properties and outstanding mechanical performance, robustness and durability.