Waterborne superhydrophobic bio-epoxy coating on Al alloy for corrosion-resistant and self-cleaning applications

Aluminum (Al) and its alloys are important engineering materials in modern industry due to their numerous advantages and have been widely used in various fields, including aerospace, marine, civilian industries and so on. However, they are prone to corrosion and contamination under harsh environmental conditions, particularly in marine environment when exposed to salty water or moisture for a long time, which can adversely affect their aesthetic appearance and desired functionalities or even cause economic losses and serious accidents. To prevent or delay the corrosion, the hydrophilic nature of Al and its alloy surfaces can be transformed to be hydrophobic or superhydrophobic. In this study, we reported an environment-friendly waterborne superhydrophobic bioepoxy coating (WSBC) without using volatile solvents. The coating is composed of bio-epoxy resin, nano silica, silane coupling agent as well as hydrophobic curing agent, and applied by spin method on Al alloy substrates. The surface morphology and roughness were characterized by a field emission scanning electron microscope (FESEM) and an atomic force microscope (AFM). The WSBC with 22.2 wt% nano silica loading without considering the solvent of deionized (DI) water displays a static water contact angle (CA) as high as 165.8 f 3.3 degrees and a sliding angle (SA) as low as 5.3 f 2.5 degrees. Electrochemical measurement results showed that the as-prepared WSBC has a significant shift from -1.160 V to -0.708 V in the corrosion potential (Ecorr) and is close to 3 orders of magnitude decrease in the corrosion current density (Jcorr), indicating the excellent corrosion resistance. The WSBC was further proven to function well after immersion in DI water and common organic solvents including ethanol and acetone for 48 h, as well as weathering resistance test. In addition, the as-prepared WSBC also showed good self-cleaning performance. The developed coating is green and no harm to human health and environment. The facile and eco-friendly process is of great importance for many industrial applications which can provide an attractive way towards anti-wetting surfaces for corrosion protection and self-cleaning effect on a variety of engineering substrates.