Electrochemical evaluation of mucilage and cochineal pigments as a hybrid film coating on aluminum surfaces

Abstract

This work deals with the electrochemical evaluation of a hybrid coating based on mucilage and prickly pear cochineal (Dactylopius coccus) for corrosion protective applications. The Opuntia streptacantha mucilage was extracted by grinding prickly pear cochineal, and three coatings containing mucilague (CM), cochineal-mucilage (CMC), and cochineal-mucilage without Tween 80 (CMC-T) were formulated. The aluminum working electrodes (WE) were coated by immersion and then left to dry for 72 hours at room temperature. The formed coats were assessed by electrochemical impedance spectroscopy, electrochemical noise, and potentiodynamic polarization curves after 24, 72, and 168 hours of immersion in a 3.5 wt% NaCl solution. These electrochemical measurements were performed in triplicate to check reproducibility. The Tween 80 plasticizer-free cochineal-mucilage-based hybrid coating reveals more excellent protection against corrosion than uncoated aluminum. Optical micrographs were used to set apart the conditions of the hybrid coating after its valuation, which show the protection of the metallic surface on which it was not coated. Results showed that the hybrid coating has suitable properties as a barrier against corrosion due to its ability to block the aggressive species diffusion by trapping them in the coating structure, which prevents their contact with the metal surface. This property is attributable to better mucilage and cochineal film homogeneity. Also, it acts as a corrosion inhibitor due to its semi-permeable behavior where only water molecules flow through its pores. This hybrid coating showed an excellent corrosion-resistant behavior to be used to protect aluminum.