Polymeric corrosion inhibitors for aluminium pigment

In aqueous alkaline media (e.g. water-borne metallic paints) aluminium pigments react by the evolution of hydrogen. This corrosion reaction can bl: inhibited by addition of different water-soluble polymers with carboxyl groups like polyacrylic acids, styrene-maleic acid or styrene-acrylate copolymers. As a rough empirical rule can be stated that the corrosion inhibiting effect of polymers with carboxyl groups increases with decreasing molecular mass and decreasing acid number. Moreover, the isoelectric point (IEP) of aluminium oxide (pH approximate to 9) seems to be an important factor controlling corrosion inhibition (and adsorption) of polymers with carboxyl groups. Thermosetting phenolic resins (resoles) inhibit the corrosion reaction of aluminium pigment excellently at pH 8 but less effectively at pH 10. The corrosion-inhibiting functional group of resoles seems to be the: chelating ortho-hydroxybenzyl alcohol structural part. In contrast, the nonionic water-soluble polymer polyvinyl alcohol does not inhibit the corrosion reaction. So, one may assume that an ionic interaction between aluminium pigment surface and polymer is necessary (but not sufficient) for corrosion inhibition. (C) 1999 Elsevier Science B.V. All rights reserved.