Ionomeric films of alginic acid

Transparent, flexible films could be made by casting aqueous solutions of alginic acid, but they dissolved in water. When films were made from a solution of alginic acid and multivalent ions, they were still water soluble. However, when alginic acid films were immersed in a solution of salts with multivalent ions, they dissolved in water much more slowly, if at all. Treatment with calcium and zinc resulted in films insoluble in water and their tensile strength increased by an order of magnitude. Iron and magnesium ions had little effect on properties of the films. Copper and aluminum showed intermediate effect, but treatment with cupric ion resulted in a fast crosslinking of the surface without affecting the inside of the film. This resulted in the formation of a tube when opposing surfaces were pulled apart.