Electrochemical Analysis Of Metal/Coatings’ Degradation Under Food Package Environment

Tinplate has good physical and chemical properties, which combines intensityand formability of steel with corrosion resistance and outward appearance beauty oftin. It is still used widely in food packaging. However, there are significant problemsrelated to the use of tinplate cans because of its poor corrosion resistance andchemical stability. The corrosion of metal may lead food contaminated and foodsafety problem, which will threaten body health of the human being. So it is a goodway that covering organic coatings on metal material, which can prevent metal releasein food packaging effectively. For corrosion problem of metal material, it is morereasonable and meaningful to sudy the different conditions the corrosion process andcorrosion mechanism in different conditions, improving coating corrosion resistance,extending the shelf life of metal packaging products, optimizing coating productionprocess.The present work studied the corrosion mechanism and microstructure propertiesof tinplate in 0.1mol/L citric acid and sodium chloride solution during naturalimmersion in aerated and deaerated conditions, using a combination ofelectrochemical measuring technology with SEM, ICP and XPS. The EIS resultsshowed that in the aerated condition, the Nyquist plots showed a characteristic withtwo time constants, indicating that the electrolyte had permeated through the defectsof the tin coating. Combined with SEM and ICP results, Fe release in solution wasin dominant, the tin coating was incomplete but still existed on carbon steel substrate.In deaerated condition, the Nyquist plots showed a characteristic with one timeconstant, Sn release was dominant, the tin coating was corroded seriously andshowed an electrochemical protective effect on carbon steel substrate.In addition to, for epoxy phenolic coated tinplate the paper studied the failureprocess of organic coating and the corrosion situation of metal matrix in a kind offunctional beverage during natural immersion for 300 days. The microstructure andelement composition of epoxy phenolic coated tinplate were observed and testedunder different immersion days. The EIS and EN were main electrochemicalmeasuring technology. According to the results, the protect property of organiccoating declined obviously at 150 days immersion. Nyquist plots showed acharacteristic with two time constants and organic coating blistered. There were obvious corrosion pit can be observed on surface of lacquered tinplate at 300 daysimmersion. At this time organic coating resistance and noise resistance decreasedsharply, the tin layer beneath the organic coating corroded seriously. The protectionperformance of organic coating had failure.