Swelling and partial solubilization of alginic acid gel beads in acidic buffer

Abstract

Swelling behaviour of alginic acid gel beads with different chemical composition, molecular weight and size was studied in acetate buffer at pH4. A correlation was observed between the swelling behaviour in this buffer and the equilibrium properties of alginic acid gels. High contents of long l-guluronic acid blocks (G-blocks), known to give a high acid gel strength, reduced the rate of swelling and also the amount of solubilized alginate molecules leaching out of the gel beads. Compared to the original alginate, the leaching molecules had a lower average molecular weight, higher content of mannuronic acid residues and a reduced average length of G-blocks. Swelling capacity, rate of swelling and solubility of alginic acid seemed to depend on a balance between the tendency of homopolymeric blocks to form intermolecular junction zones, and the tendency of alginate to reduce the chemical potential of water. As expected, swelling rate increased with increasing temperature and decreasing bead size.