Exopolysaccharides (EPS) as anti-corrosive additives for coatings

Exopolysaccharides (EPS) are a class of renewable polymers that show interesting anti-corrosive properties and could potentially be used as an alternative for zinc phosphates. When combined with a waterborne styrene-acrylic polymer dispersion (SA-1), exopolysaccharides were shown to give an improvement in the anti-corrosive performance. Electrochemical studies show higher charge transfer resistance (R _ct) values for the SA-1/EPS combinations as compared to the SA-1 itself suggesting that in the presence of EPS less corrosion took place. Outdoor exposure test shows that the presence of EPS188 gave good corrosion protection for up to a year when exposed under marine conditions. The distribution of EPS modification throughout the coating was made visible using Confocal Laser Scanning Microscopy and indicated that EPS was distributed rather homogeneously. A working mechanism was proposed in which the carboxylic acid groups on the oxidised EPS form a complex with iron ions formed by the anodic reaction and this insoluble complex forms a protective layer between the coating and metal. The results in this paper show that by using renewable polysaccharide additives the anti-corrosive coating performance can be improved.