In this work, urea-formaldehyde resin was applied to enhance the corrosion protection properties of an epoxy coating. The urea-formaldehyde (UF) resin was synthesized through in situ polycondensation and the coatings were prepared by ball-milling grinding. The UF powder and coatings were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), sedimentation test, and electrochemical impedance spectroscopy (EIS). One major finding was that superior compatibility of UF resin with epoxy resin retained the high dispersion of UF in polymer matrix, leading to barely reunion during grinding. UF presented nano-scale size after grinding as shown by TEM measurements. In addition, there was not any flaw revealed from cross-sectional microstructural features of coatings. The UF resin has effectively prevented the corrosive medium from further permeating through diffusion channels to the interface between coating and steel substrate. Results further revealed that the UF resin could significantly reinforce the corrosion protection property of epoxy coatings on carbon steel substrate.
The corrosion of metallic materials poses a great threat to humans. Unfortunately, corrosion cannot be fully prevented, but only retarded and minimized. Many corrosion control strategies are currently available, such as the use of corrosion inhibitors, electrochemical cathodic protection, surface treatments, and coatings.1, 2, 3, 4 Among them, the use of protective coatings is attracting global attention because of their convenient construction and outstanding protection.5, 6, 7 Epoxy resin coatings are widely used because of their versatility, superior adhesion onto various substrates, high resistance to chemical solutions, intrinsic toughness, excellent electrical resistance, and durability at high and low temperatures.8, 9
However, the corrosion protection capability of neat epoxy resin coating is limited by the hydrolytic degradation after exposure to corrosive electrolyte. Corrosive media, such as oxygen, water, and chloride ions, reach the substrate/coating interface through diffusion channels.10 Adhesion is then lost, and the coating deteriorates.