Ionomeric films of alginic acid

Transparent, flexible films could be made by casting aqueous solutions of a lginic acid, but they dissolved in water. When films were made from a solut ion of alginic acid and multivalent ions, they were stilt water soluble. Ho wever, when alginic acid films were immersed in a solution of salts with mu ltivalent ions, they dissolved in water much more slowly, if at all. Treatm ent with calcium and zinc resulted in films insoluble in water and their te nsile strength increased by an order of magnitude. Iron and magnesium ions had little effect on properties of the films. Copper and aluminum showed in termediate effect, but treatment with cupric ion resulted in a fast crossli nking of the surface without affecting the inside of the film. This resulte d in the formation of a tube when opposing surfaces were pulled apart.