Hybrid alginate based aerogels by carbon dioxide induced gelation: Novel technique for multiple applications

This paper presents a technique of manufacturing alginate-based hybrid aerogels. The technique involves mixing a second component (biopolymers or filler materials) in sodium alginate solution and crosslinking with carbonates of metals like calcium, strontium, cobalt, nickel, zinc and copper. Various biopolymers (lignin, starch, pectin, carrageenan, methyl and carboxymethyl cellulose, gellan gum, and gelatin), polymers (PVA, PEG, Pluronic P-123), inorganic (sodium silicate) and filler materials (titania and hydrophobic silica) were used as the second component. It is suggested to use pressurized carbon dioxide (5 MPa) for gelation and supercritical CO2 drying (10–12 MPa) to yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.017 g/cm3), high specific surface area (200–800 m2/g) and pore volume (2.3–9.5 cm3/g for pore sizes < 150 nm). Basic examples expressing the applicability of these aerogels are demonstrated such as in the field of thermal insulation (thermal conductivity in the range 18.5–21.6 mW/m K). Extension of carbon dioxide gelation technique from metal-crosslinked alginate-based system to other biopolymers (cellulose and chitosan) is also demonstrated.