Advanced electrochemical methods for food can evaluation

Abstract

Electrochemical measurements have been used to investigate the corrosion resistance of food cans produced from a steel–polymer laminate material, Ferrolite, over periods of up to 30 days. The aim of this work was to develop a predictive corrosion test procedure, whereby short term results could be used to predict long term container performance. Electrochemical impedance spectroscopy (EIS) and dc linear polarisation techniques were used to study the effect of increasing polymer laminate film thickness, and to compare Ferrolite performance with that of a conventional vinyl organosol lacquer. Testing was carried out using a sealed in electrode system, where electrodes were fitted to commercial can ends before filling. This electrode system was found to perform well over a 30 day period, and the results indicate that Ferrolite cans possessed a significantly greater resistance to corrosion than conventionally lacquered cans. Predictably, as the Ferrolite film thickness increased, coating and polarisation resistance values also increased. Under pack test conditions, coating and polarisation resistance parameters initially decreased rapidly, which is consistent with hydration and ion migration processes occurring within the film. After 30–40 days, the rate of change in resistance decreased and was consistent with longer term degenerative effects such as corrosion. Coating resistance, as determined by EIS, was found to be largely independent of the electrolytic oxygen concentration; however, polarisation resistance, determined by dc measurements, showed a strong inverse dependence on oxygen concentration.