Outdoor sculptures are continually exposed to the elements, including acid rain. Pollutants in the atmosphere endanger the composition, color, and degree of corrosion on outdoor objects. Bronze is especially susceptible to deterioration caused by atmospheric corrosion. When unprotected bronze is exposed to acidic conditions, corrosion products-including soluble salts-are formed. These salts wash away during rainfall, resulting in discoloration and pitting. Therefore, delaying corrosion is a crucial element of maintaining outdoor bronze and is a constant battle for conservators. Coatings are often used to help protect bronzes from destructive erosion caused by outdoor weathering. Experiments directed at developing new coating systems for bronze have been a focus of research at North Dakota State University. To better understand the coatings' behaviors and respective lifetimes, the coated bronze has been exposed to accelerated weathering. The research has focused on creating viable coatings that afford protection to the underlying bronze surface while remaining removable per the needs of conservators responsible for heritage preservation. Typical polyurethane coatings are very durable and, when applied to metals, provide a high degree of protection. The disadvantage of using polyurethanes is that they are designed to be permanent and only removable by mechanical methods. Through this research, we are attempting to develop a modified polyurethane clear coat that is both protective and removable. This paper will discuss the synthesis and evaluation of the polyesters, combinatorial formulation and evaluation of the materials, as well as their potential for use in a crosslinked, removable system.
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