Conventional coating films are typically solvent based and contain a high percentage of volatile organic compounds (VOCs), which are environmentally damaging and pose health risks to humans. Recent developments have led to the introduction of water-borne, low-VOC coating systems. Research into the bulk material properties of these low-VOC coatings was necessary to understand the degradation process of the coatings. In this study, researchers worked to determine the water sorption properties of two water-borne, and two solvent-based coating film systems. Water sorption properties of a material can be characterized by two primary properties, the diffusion coefficient and saturated water content. These two properties were measured for individual layers of each coating film system, multi-layer samples of each coating film, and samples of each coating bonded to a steel substrate. By comparing the individual layer, multi-layer, and substrate-bonded samples, the researchers determined the effects that the bulk material, the interface between separate layers, and the interface between coating and steel have on the overall properties of the coating. Stress relaxation measured the rate of decay of stress incurred in a coating after being deformed by applied strain. These data were correlated with the fractional water content of each coating at the time of testing. Finally adhesion testing determined a coating’s ability to remain bonded to a steel substrate under tensile stress in both dry and saturated conditions. The study is discussed in CORROSION 2014 paper no. 4018, “Kinetic Water Sorption Behavior of Water-Borne Urethane/Epoxy Coating and Its Effect on Mechanical Strength,” by Y. Takeshita, T. Miwa, E. Becker, S. Sakata, T. Kamisho, and T. Sawada.
