Waterborne bio-based epoxy coatings for the corrosion protection of metallic substrates

Corrosion of engineering metals and alloys poses a threat to the safety and reliability of engineering structures. In this work, an environmentally-friendly hydrophobic coating was developed based on a bio-based epoxy with addition of nanoparticles, a silane coupling agent (3-glycidyloxypropyl) trimethoxysilane (GLYMO), and a hydrophobic curing agent. This coating was applied onto Fe substrates via spin-coating. The water contact angle of ^∼153.0° and sliding angle of ^∼14.3° were obtained for an optimal coating with 25.0 wt.% nanoparticles loading. The prepared coating exhibited high hydrophobic performance when immersed in water and common solvents including ethanol and acetone for 48 h. Besides, after exposure to continuous cycles of UV irradiation and water condensation for 24 h, this optimal coating was able to retain a high hydrophobicity at contact angle of ^∼142.7°, indicating its good weathering resistance. Furthermore, the electrochemical measurements demonstrated that the optimized coating displayed a 2-orders-of-magnitude reduction in its corrosion current density and a positive shift of 0.344 V in its corrosion potential. The corresponding inhibition efficiency was 93.75%. The adsorption energy and diffusion coefficient were calculated using molecules dynamic simulation to further understand the corrosion inhibition behavior at the molecular scale. This green and bio-based water-repellent epoxy coating holds great potential towards corrosion inhibition for other metallic structures in harsh working environment.