Dextrine-modified chitosan marine polymer coatings

In trying to modify partially acetylated chitosan (CS) marine polymers ground from crab or shrimp shells for use as environmentally benign water-base coatings for aluminum (Al) substrates, CS was dissolved in a solution of HCL acid, and then mixed with corn starch-derived dextrine (DEX) containing Ce nitrate as oxidizing agent in aqueous medium. This blend of polysaccharides was deposited on Al surfaces by a simple dip-withdrawing method, and then heated at 200 degrees C to transform the liquid layer into a solid film. The solution --> solid phase transition provided the changes in the molecular conformation of CS and DEX; the former was transformed into deacetylated poly(D-glucosamine) and the latter referred to the formation of Ce-complexed carboxylate fragments. Furthermore, the chemical reactions between the NH2 groups in deacetylated CS and the carboxylate fragments led to the creation of amide linkages that served in grafting DEX fragments onto the CS. Such fragment-grafted CS polymer coating films deduced from the proper proportions of CS to DEX offered great film-forming performance, low susceptibility to moisture, and low ionic conductivity, conferring a salt-spray resistance of 720 hours. (C) 1999 Kluwer Academic Publishers.