Dynamic mechanical analysis of novel polyurethane coating for military applications

Three polyurethane coatings were evaluated using DMA to investigate the rel ationship between dynamic mechanical properties and durability properties o f coated test panels. The current polyurethane solvent-based formulation, u sed as a chemical agent resistant camouflage top coat on all military tacti cal vehicles, was investigated along with newly developed water-reducible ( WR) polyurethane coatings. The WR coatings offer significantly reduced vola tile organic compounds (VOCs) compared to the solvent-based system, and thu s represent environmentally compliant coatings. DMA investigations revealed that the two classes of polyurethane coatings exhibit different dynamic me chanical properties, which are attributed to different cross-linking mechan isms involved in film formation. The more uniformly cross-linked solvent-ba sed coating provides the best chemical agent resistance but the poorest mec hanical properties. Properties measured using DMA were sensitive to the deg ree of isocyanate to hydroxyl indexing in the WR formulations as well as th e drying time of coatings prior to evaluation. DMA investigations indicated that longer cure times at ambient temperature (6 or more months) may adver sely affect the mechanical properties of the solvent-based system and poten tially enhance chemical agent resistance of the WR coating. Further studies involving aged coatings are planned. Published by Elsevier Science B.V.