Poly(itaconic acid)-modified chitosan coatings for mitigating corrosion of aluminum substrates

Abstract

To make a water-insoluble chitosan (CS) biopolymer, the synthetic poly(itaconic acid) (PIA) polymer was added to graft it onto the liner CS chains and to crosslink between the CS chains. The grafting and crosslinking reactions were generated by a strong chemical affinity between the NH 2 groups in the CS and the COOH groups in the PIA, leading to the formation of amide bonds. When this polymer was applied as environmentally benign water-based coatings to an aluminum (Al) substrate by a simple dip-withdrawing method, the following three factors played an essential role in mitigating the rate of corrosion of the Al: first was the polymer’s conformation containing hydrophobic amide bonds, together with a minimal amount of hydrophilic unreacted COOH in PIA and NH 2 in CS; second was the lesser susceptibility of the coating films to moisture due to the enhanced degree of grafting and crosslinking; and third was the interactions at the interfaces between the grafted CS and the Al substrate, developing the formation of the –COO–Al linkage. The PIA-grafted and -crosslinked CS polymer coating films generated from the proper proportions of PIA to CS included all these factors and displayed low ionic conductivity, thereby imparting a salt-spray resistance of 694 h for coated Al panels.