Replacement of traditional seawater-soluble pigments by starch and hydrolytic enzymes in polishing antifouling coatings

The use of starch and hydrolytic enzymes as replacement for traditional polishing pigments (e.g., Cu2O and ZnO) in antifouling coatings has been investigated. The enzymes facilitate a slow conversion of water-insoluble starch into water-soluble glucose, and dissolution of glucose causes the development of a leached (porous) layer in the wetted, outermost part of the coating. Subsequent water–binder interaction at the pore walls gives rise to polishing, in a manner similar to that of conventional antifouling coatings. Different starch types have been evaluated and classified as potential coating ingredients, and the impact of the addition of starch on the functional properties of the coating is described. Starches from rice, corn, and tapioca have been tested, and due to a smaller amount of water-soluble content and lesser tendency to agglomerate, corn starch is preferred. Leaching occurs in all the starch-enzyme coatings tested; however, polishing is only detected for two out of four binder systems investigated. Suitable polishing rates of 7–10 μm/month, based on the enzymatic starch-degradation, have been measured. Controls containing only starch (no enzyme) did not polish.