Anti-corrosion behavior of layer by layer coatings of cross-linked chitosan and poly(vinyl butyral) on carbon steel

Anti-corrosion coatings of chitosan were fabricated by layer-by-layer (lbl) addition of chitosan (Ch) and poly vinyl butyral (PVB) on mild carbon steel substrate. Corrosion inhibition of chitosan in lbl coatings was analyzed by electrochemical, spectroscopic and morphological measurements. Sandwiching of chitosan between two hydrophobic PVB layers enhanced its bonding strength and enabled the amine and hydroxyl groups of chitosan to chelate with iron ions that led to the formation of a chitosan stabilized iron oxide passive layer on the metal surface. Effect of chitosan crosslinking on the stabilization process of passive oxide layer as well as the coating stability was studied by incorporating glutaraldehyde in the chitosan layer. The results obtained from electrochemical impedance spectroscopy and Tafel plots clearly showed a superior corrosion protection of lbl coatings generated by 1 % glutaraldehyde incorporation in the middle chitosan layer. SEM and Raman spectra confirmed the formation of passive oxide layer on the metal surface stabilized by chitosan polymer backbone. Improvement in the anti-corrosion properties of PVB_Ch/1 %Glu_PVB coatings were not observed after the incorporation of fillers like graphene and vermiculite in the chitosan layer probably due to the imperfect adhesion of the fillers with the polymeric matrix.