Characterization of graphene oxide pickering emulsion and silica nanoparticles for waterborne epoxy coating

Abstract

The application of epoxy resins as the anticorrosion coating has obtained widespread application because of their superior adhesion to various substrate and excellent chemical inertness. However, epoxy resin tends to form microcracks and the VOCs released during the drying process is harmful. Although the waterborne epoxy coatings are a much safer alternative, they are prone to swell caused by water absorption. With the consideration for the environment and human health in mind, this research aimed at developing a new and improved waterborne coating that employed graphene oxide (GO) encapsulated linseed oil and silica nanoparticles (SiO2) as healing microcapsules and anticorrosion agent respectively. This research was divided into three main phases; phase (A), synthesis of graphene oxide microcapsules (GOMs) via Pickering emulsion method, phase (B), synthesis of amine-stitched graphene oxide microcapsules (Amine-stitched GOMs), and phase (C), preparation of coating sample. GO was selected as the microcapsule’s shell due to its flexibility and excellent barrier properties, while the linseed oil core is able to polymerize when in contact with the atmosphere to form a hydrophobic film. SiO2 was used to increase the density and adhesion between the coating and the substrate. This coating was formulated through the copolymerization of waterborne epoxy resin with the incorporation of GOMs and SiO2 nanoparticles. Waterborne epoxy acted as a matrix while GOMs and SiO2 nanoparticles act as a guest component. The coating was directly applied on carbon steel type S50C as the substrate. The test of adhesion, immersion, and salt spray was conducted in accordance with ASTM D3359, B895, and B117-94 respectively. The POM, TGA, and TEM showed that the GOMs were successfully synthesized, having a size ranging from 5.39 µm to 20.45 µm, coefficient of variation (Cv) of 0.34, shell thickness around 140 to 160 nm, and 94% loading capacity. Based on the physical analysis and corrosion test, the addition of GOMs and SiO2 nanoparticles reduced the swelling degree and corrosion rate of a waterborne epoxy coating by 54.1% and 62.7% respectively. The novel formulated coating also demonstrated good adhesion to the metal substrate and possess the ability to perform as a self-healing coating. Incorporation of 10 wt% GOMs and 1 wt% of SiO2 nanoparticles were identified as the best composition for waterborne epoxy coating in improving waterborne coating properties.