Effects of prolonged saline water exposure on the peel strength of polyurea/monel 400 interface

This study investigates changes in the peel strength of polyurea/monel 400 interfaces after prolonged exposure to saline water. The monel family of alloys is extensively used on marine structures due to its resistance to corrosion, and polyurea has shown considerable promise as a coating material for marine structures to mitigate the damage from blast loading and provide corrosion resistance. In the present work, polyurea was cast on sandblasted and chemically treated Monel 400 bars, which were subsequently immersed in saline water at 70°C for 2, 5 and 8 weeks, respectively, to accelerate the aging process. This high-temperature exposure corresponded to 19, 48 and 76 weeks in the real-life service environment. The peel strengths of the interfaces were measured using the fixed arm peel test at two angles: 90° and 180°. The adhesive energy was computed from the experimentally determined peel strength using models developed by Kendall and Rivlin. The surfaces exposed by peeling were analyzed with the use of an optical microscope to determine the different failure modes at the interfaces. Finally, employing degradation kinetics, a degradation model was established and used to calculate long-term adhesive energy and the degradation rate of the interface. Results showed that prolonged exposure to saline water leads to a drop in the peel strength. For 180° peel test, an 83% decrease in the peel strength of the polyurea/monel 400 interface was observed after 8 weeks of exposure at 70°C. Both peel angles gave similar adhesive energies for the same exposure durations indicating the independence of the adhesive energy on the testing angle. The elastic term contribution to the adhesive energy for all experiments was less than 5.5%. Lastly, the exposure time dependence on the adhesive energy followed first-order degradation kinetics.