Protective polymeric films for industrial substrates: A critical review on past and recent applications with conducting polymers and polymer composites/nanocomposites

Corrosion defined as the deterioration of a material when it interacts with its environment is a global problem. Among the different strategies employed to combat corrosion, the use of coatings and corrosion inhibitors are the most popular. Coatings or corrosion inhibitors form a layer over the metallic substrate and protect it against corrosion. Polymers, both naturally occurring and synthetic have been tested for metal corrosion protection as replacement for the toxic inorganic and organic corrosion inhibitors. Interest in them stems from their availability, cost effectiveness, and eco-friendliness (especially for natural polymers) in addition to the inherent stability and multiple adsorption centers. However, it is found that most polymeric materials studied are moderate corrosion inhibitors. Several attempts such as copolymerization, addition of substances that exert synergistic effect, cross linking, blending, and most recently incorporation of inorganic substances in nano size into the polymer matrix have been made to improve the inhibition ability of polymers. In this review, the application of conducting polymers, polymer composites and nanocomposites for corrosion protection of different industrial metal substrates are explored based on reported experimental data and their mechanism of inhibition explained. Some identified drawbacks and future direction in this area have also been highlighted.