A gelling polysaccharide extracted from giant brown seaweed. It is a straight chain, colloidal, polyuronic acid composed mainly of anhydro-b-D-mannuronic acid residues linked in the 1---->4 position. It has been used in the flocculation of solids in water treatment; as sizing agent; thickener; emulsion stabilizer; and a suspending agent.Due to its gelation properties, it is used in the preparation of colloidal biodegradable structures such as gels, biofilms, beads, nanoparticles, and microcapsules suitable for applications that range from gel-based separation technologies to drug delivery and cell preservation.

• Molecular Formula:(C₆H₇O₆Na)_n
• Synonyms:Algin; Sodium alginate; Sodium polymannuronate; Kelgin; Protanal
• Physical Description:White to cream coloured powder
• Solubility:Soluble in water, forming a viscous, colloidal solution. Insoluble in alcohol and in hydro-alcoholic solutions in which the alcohol content is >30% w/w. Insoluble in chloroform, ether, in aqueous acid solutions when the pH is below 3.
• Viscosityof a 1% aqueous solution (25C) is approximately <300>