Water Transport in Polymer Coatings and the Correlation Between Coating Properties and Water Uptake in Aqueous Solutions at Elevated Temperatures

The effect of water sorption on the properties of two polymer coatings for pipelines was studied. Water transport in both coatings during the early stages of diffusion followed Fickian behavior but showed non-Fickian behavior during long immersion times with a decrease in the water diffusivities. The increase in the coating capacitance correlated well with the amount of water absorbed in the coatings. The coating impedance during long-term immersion tests decreased exponentially with increased water saturation fraction of the coating and with increased solution temperature. The glass transition temperature of wet coatings was strongly dependent on the temperature of the soaking solution and the immersion time. The effect of the glass transition on the impedance, capacitance, and break point frequency of these coatings during immersion tests was not significant.