(698i) Modeling Hydrothermal Degradation of Thermosets and Its Impact on Mechanical and Thermal Properties

Thermoset coatings are widely used for providing thermal insulation to sub-sea oil pipelines. These coatings are expected to have a lifetime of over several years. However, chemical reactions with water often degrade the thermoset network over time and cause changes in several physical properties of the coating. Of these, thermal conductivity and mechanical strength are critical to the marine thermal insulation application. In order to estimate the lifetime of the coatings it is important to understand how these two properties change over time. In this talk we will present a modeling approach to predict these changes. There are three main rate processes that determine how the network evolves over time: (i) water diffusion, (ii) heat conduction, and (iii) kinetics of the reactions between the network and water. The parameters for modeling water diffusion and heat conduction processes were determined from standard water uptake, differential scanning calorimetry, density and heat conductivity measurements. Rate constants for the reaction kinetics were estimated by fitting the concentration profiles of extractable fragments generated during isothermal ageing in water at different temperatures. A model combining the three processes was built to predict the spatial and temporal evolution of the concentration of unreacted end-groups in the coating. Miller-Macosco analysis was used to convert the concentration of unreacted end-groups to cross-link density under the assumption that the network breaks in the same way as it is created. The evolution of heat conductivity, elastic modulus and tensile strength of the coating was determined from the predicted cross-link density profiles based on established relationships. The approach described in this presentation has general applicability and can be used in conjunction with accelerated ageing tests to build confidence around the lifetime of thermoset coatings.