Advanced electrochemical methods for food can evaluation

Electrochemical measurements have been used to investigate the corrosion re sistance of food cans produced from a steel-polymer laminate material, Ferr olite, 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 u sed to predict long term container performance. Electrochemical impedance s pectroscopy (EIS) and de linear polarisation techniques were used to study the effect of increasing polymer laminate film thickness, and to compare Fe rrolite performance with that of a conventional vinyl organosol lacquer. Te sting was carried out using a sealed in electrode system, where electrodes were fitted to commercial can ends before filling, This electrode system wa s found to perform well over a 30 day period, and the results indicate that Ferrolite cans possessed a significantly greater resistance to corrosion t han conventionally lacquered cans. Predictably, as the Ferrolite film thick ness 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 mig ration processes occurring within the film. After 30-40 days, the rate of c hange in resistance decreased and was consistent with longer term degenerat ive effects such as corrosion. Coating resistance, as determined by EIS, wa s found to be largely independent of the electrolytic oxygen concentration; however, polarisation resistance, determined by de measurements, showed a strong inverse dependence on oxygen concentration, (C) 1999 loM Communicati ons Ltd.