Nano-scale mechanical and wear properties of a corrosion protective coating reinforced by cellulose nanocrystals - Initiation of coating degradation

Organic coatings are commonly used for protection of substrate surfaces like metals and wood. In most cases they fulfil their purpose by acting as a barrier against unwanted substances such as oxygen, water or corrosive ions. However, with time coatings fail due to degradation caused by chemical reactions or wear by wind, water, impact of solid particles or sliding motions against other solid objects. In this work we focus on a nanocomposite anticorrosion coating consisting of a hydroxyacrylate-melamine matrix that has been reinforced by a small amount (0.5 wt%) of cellulose nanocrystals. This nanocomposite is of interest as it has shown favourable corrosion protection properties on carbon steel. Here we investigate the nanomechanical and nanowear properties of the coating in air and in water, and we also explore how these properties are affected by exposure to a corrosive 0.1 M NaCl solution. Our data show that the nanomechanical properties of the coating surface is strongly affected by the environment (air or water), and that exposure to the corrosive solution affects the coating surface well before any deterioration of the corrosion protective properties are found. We suggest that our experimental methodology constitutes a powerful way to investigate and understand the initiation of coating degradation.