Some consequences of saline solution immersion on mechanical behavior of two marine epoxy-based coatings

We report the results of static and dynamic mechanical measurements carried out on two epoxy-based coatings with different contents of sodium chloride solution. Both coatings presented strong lixiviation processes in saline solutions in parallel with water absorption. This was interpreted as a polymer density loss where ionic species are strongly involved and that may lead to a change of the mechanical properties of the coating. The mechanical behavior of both coatings showed clearly three domains (elastic, visco-elastic and visco-plastic), which depend on the solution ingress. In agreement with previous results obtained on epoxies, the Young modulus decreases with the solution content. Visco-elastic (VE) and visco-plastic (VP) behavior dependence with solution ingress showed two antagonist phenomena: softening (elongation increase) and hardening (ultimate stress increase). The first one is classically associated with plasticization while hardening is mainly linked with the development of internal stresses. These phenomena were correlated with the cross-linking density distribution within the coatings.