Abstract
Polymeric coatings may act as a physical barrier between the aggressive ions and the metal substrate. However, prolonged exposure may cause damage to the polymer coating, leading to a continuous reduction of the barrier effect and consequently loss of the corrosion protection. The objective of this study is to determine the effect of aminopropyltriethoxysilane (APS), cellulose and polyaniline emeraldine-salt (PAni ES) in an epoxy coating on the corrosion protection of mild steel. Microcrystalline cellulose (MCC) and cellulose nanowhiskers (CNW) functionalized or not with PAni ES were used and compared. The coating properties were investigated by electrochemical impedance spectroscopy (EIS), salt spray test and scanning electron microscopy (SEM). The surface of the carbon steel, after 1000 h of exposure, did not present evidence of superficial corrosion. Polymer coatings using CNW and PAni ES showed improved corrosion protection properties even after 90 days of immersion in 3.5 wt% NaCl solution. The greatest increase in the corrosion resistance of the coating was found by EIS for the epoxy coating reinforced with CNW functionalized with PAni ES, revealing a synergistic effect of the electroactivity of a conducting polymer and nanosized cellulose particles.
Highlights
Polymeric coatings are widely used as a common, practical and cost-effective method to protect metal surfaces from environment action
The electrochemical response for the RE APS-Zr coating (Figure 2a) did not represent a true capacitor and the characteristic semicircle was suppressed in the Nyquist plot
The formation of a second semicircle at low frequencies suggests that electrochemical reactions at the coating/metal interface progress due to the electrolyte access to the metal substrate[25,26]
Summary
Polymeric coatings are widely used as a common, practical and cost-effective method to protect metal surfaces from environment action. The corrosion performance of polymeric coatings depends upon several parameters such as adhesion to the metal substrate, permeability, thickness, chemical and mechanical resistance in aggressive environments. To the properties of the coatings, the metal pretreatment before their application represents an important role on the corrosion performance and must be carefully conducted to provide effective protection. By using zirconium conversion coatings, sludge and cleaning baths are reduced, lessening the generation of effluents. These coatings require a shorter operation time than other conventional treatments[4]
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