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Drying of cellulose nanocrystal gel beads using supercritical carbon dioxide

Li, Yiwen, Jiang, Hua, Han, Binbin, Zhang, Yang
Journal of chemical technology and biotechnology 2019 v.94 no.5 pp. 1651-1659
aerogels, carbon dioxide, cellulose, drying, microstructure, nanocrystals, porosity, shrinkage, solvents, surface area, temperature
BACKGROUND: The effects of the conditions for the supercritical carbon dioxide (scCO₂) drying of cellulose nanocrystal (CNC) wet gel were investigated on the residual solvent content, the shrinkage and the microstructure of the ensuing aerogel. RESULTS: The scCO₂ drying of CNC wet gel could be divided into a spillage phase and an extraction phase. In the first phase, just a very short time after the beginning of drying, shrinkage occurred and more than half of the solvent was removed. No further shrinkage was observed thereafter, but the solvent continued to be exponentially removed. Increasing pressure, temperature and time were favorable for solvent removal and the reduction of aerogel shrinking. The shrinkage increased the pore size inside the aerogel and made the outer surface of the CNC aerogel much denser than its interior. To preserve the original microstructure of the wet gel, the optimal drying was performed at 11.04 MPa and 40 °C for 120 min. At these conditions, the shrinkage ratio was only inversely proportional to the CNC content in the wet gel. CONCLUSION: CNC aerogel was obtained with a shrinkage ratio of 3.1%, a surface area of 387 m² g⁻¹ and an average pore size of 7.2 nm using 3.0% (w/w) CNC wet gel. © 2019 Society of Chemical Industry