Eco-friendly conversion coating for the protection of aluminium alloys in the food/beverage canning industries

Abstract

In view of environmental and health challenges associated with conversion coatings derived from heavy metal ion compounds, this work reports the development and performance of water extracts of Hibiscus sabdariffa (HS) calyces (Hibiscus flower), as a starting green inhibitor in the development of environment friendly, non-carcinogenic conversion coating on aluminium alloy for application in the canning and food packaging industries. Gravimetric analyses revealed that the coating developed sluggishly, a coating weight of about 3 mg was attained after 30 mins of treatment in the coating bath. Fourier transform infrared spectroscopy (FTIR) analyses showed that the coating solution and the coating materials stripped from the aluminium alloy substrate had identical functional groups which were either shifted down or upfield in the FTIR spectra of the coating. However, scanning electron microscopy (SEM) examination revealed that the thin coating developed on aluminium mapped the grain and sub grain boundaries of the substrate. Whereas, within the detection limits of the EDS, the coating is composed essentially of carbonaceous compounds of aluminium and its oxides as well as those of the other elements present in the substrate and in the coating solution. These compounds are probably hydrated. The corrosion performance and adhesion characteristics of the HS coating were better than for the ‘bare’ aluminium alloy substrate.