engleski

Polyphenols - environmentally friendly corrosion inhibitors of tin

Most of the well-known inhibitors of corrosion are organic compounds that contain nitrogen, sulphur, oxygen and double bonds through which they are adsorbed onto the metal surface. Their synthesis is very often expensive, and they exert some toxic effects, harmful for human beings as well as for environment. Therefore, it is necessary to use nontoxic substances as corrosion inhibitors, especially in food industry. Much of attention is currently being paid to the possible health benefits of dietary flavonoid polyphenols and other phenolic compounds, which are constituents of fruit, vegetables and beverages. They are present in cocoa and chocolate, too. Therefore, it seemed interesting to investigate the effects of these valuable natural compounds on corrosion process of tin, an ambalage material used in food industry. The polyphenols were extracted from cocoa liquor with aqueous acetone and aqueous methanol and the extracts obtained were analysed by reversed-phase liquid chromatography (RP-LC) with UV-Diode Array detection. The identified compounds were flavanols (+)-catechin, (-)-epicatechin and their polymers procyanidins. The tin corrosion inhibiting efficiency of (-)-epicatechin, (+)-catechin, aqueous acetone and aqueous methanol extracts of cocoa in 3 % sucrose solution was determined by weight loss method and polarization resistance method. The degrees of protection were calculated on the basis of the values obtained for rate and current corrosion process of tin. The results confirmed that all the compounds and extracts examined act as tin corrosion inhibitors, the best being (+)-catechin solution in concentration 10-5 mol dm-3.

(+)-catechin; (-)-epicatechin; cocoa liquor; electrochemical measurements

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