Preparation of cellulose aerogel by the salt-induced gelation

For the cellulose-7% NaOH-12% urea aqueous solution, adding inorganic salts can induce and accelerate its gelation process. The inorganic salts show a remarkable accelerating effect on the gelation with the sequences as K⁺>Na⁺>Li⁺ for cations and Cl^->Br^->NO₃^- for anions. For all kinds of salts used, the gelation rate increases with the increase of the salt dosage. Based on this result, a new preparation method of cellulose aerogels has been proposed using inorganic salt-induced gelation followed by solvent exchange and supercritical CO₂ drying. According to the SEM, N₂ adsorption and mercury intrusion measurements, the porous structure of cellulose aerogel made through salt-induced gelation is characterized as follows: in the mesopore range, the specific surface area is 284 m²/g, the pore volume 2.0 cm³/g and the average pore diameter 20.5 nm, in the macropore range, the pore volume is 13.95 cm³/g, the average pore diameter 0.732 μm and the porosity 91%.