Improving the barrier properties of chitosan coatings through Schiff base formation and halloysite incorporation for corrosion protection of commercially pure aluminum (cp-Al).

Coatings of chitosan modified with vanillin and containing halloysite nanotubes as filler were produced for corrosion protection of commercially pure aluminum (cp-Al). Modifications were characterized by Fouriertransform infrared spectroscopy (FTIR) and the degree of modification was determined by the ninhydrin assay, using UV-vis spectroscopy. Chitosan-modified coatings had their anticorrosive performance evaluated in 3.5 wt% NaCl solution through linear polarization and electrochemical impedance spectroscopy (EIS). Results showed an increase in the anticorrosive efficiency of the films with the increase of the degree of modification, which was related to the decrease of the electrolyte permeation through the coatings. The effect of the filler's addition was evaluated by EIS analysis, SEM images coupled with EDS and analysis of the degree of swelling in 3.5 wt% NaCl. The electrochemical assays demonstrated that the addition of halloysite in low concentrations (up to 1%) improves the barrier properties of the films leading to a higher anticorrosive efficiency. It was also observed that with 10% halloysite occurs a phase separation responsible for the expressive increase in the degree of swelling of the samples and loss of barrier properties.