Dynamic mechanical analysis of novel polyurethane coating for military applications

Three polyurethane coatings were evaluated using DMA to investigate the relationship between dynamic mechanical properties and durability properties of coated test panels. The current polyurethane solvent-based formulation, used as a chemical agent resistant camouflage top coat on all military tactical vehicles, was investigated along with newly developed water-reducible (WR) polyurethane coatings. The WR coatings offer significantly reduced volatile organic compounds (VOCs) compared to the solvent-based system, and thus represent environmentally compliant coatings. DMA investigations revealed that the two classes of polyurethane coatings exhibit different dynamic mechanical properties, which are attributed to different cross-linking mechanisms involved in film formation. The more uniformly cross-linked solvent-based coating provides the best chemical agent resistance but the poorest mechanical properties. Properties measured using DMA were sensitive to the degree of isocyanate to hydroxyl indexing in the WR formulations as well as the drying time of coatings prior to evaluation. DMA investigations indicated that longer cure times at ambient temperature (6 or more months) may adversely affect the mechanical properties of the solvent-based system and potentially enhance chemical agent resistance of the WR coating. Further studies involving aged coatings are planned.