Effects of Marine Environments on the Mechanical Response of Polymeric Coatings

Abstract

Polymeric materials are an important part to marine structures as they provide protection from the harsh underwater environment. While they can be used in many other applications, they can be found as a coating on propellers, boat and ship hulls, and even protective coatings for electronics. Given the service environment of these polymers, it is important to understand how they are affected by their surroundings. Three polymers were studied in different conditions; two polyurethanes and a polyurea. Each polymer underwent different experiments to determine how they would be affected by the environmental factors they would be exposed to.Polyurea is a very durable polymer with excellent mechanical and chemical properties. It is wear and corrosion resistant which makes it an optimal choice for naval applications. The US Navy uses polyurea as a protective coating on marine structures which expose it to aggressive marine environments, i.e. low temperatures, sea water, and possible high strain rate loadings. This work investigates the effects of low temperature coupled with saline water weathering at multiple strain rates. For this study, a range of tests were conducted: low temperature (-2°C) and room temperature, virgin and weathered specimens, low and high strain rates, and a combination of those mentioned. Specimens which were weathered were exposed to saline water for 2 weeks in an accelerated weathering facility. This simulates 4.4 months in real life time at 17°C and 12 months at -2°C. An insulated box with cold flowing air was used to obtain the low temperature. A universal testing machine and a modified Split Hopkinson Pressure Bar were used to obtain strain rates of 10-3 to 103. Results show polyurea's response in highly sensitive to the given parameters, where weathering has the dominant effect. In the marine industry, polyurethanes are a well-known material for use as they are water and tear resistant. Their properties allow the material to be an excellent choice for encapsulants for cable connectors and circuitry which during its service life may come in contact with sea water. In order to better understand how this material changes over time when exposed to sea water, a polyether-based polyurethane was studied after long term exposure to saline water using accelerated weathering techniques. The specimens were weathered in 3.5 % saline water at 70°C for 10, 48, 85, and 129 days simulating 1 month, 4.5, 8 and 12 months in real life service time, respectively. The quasi-static (2 x