Yiwen Li,a Hua Jiang,a* Binbin Hana and Yang Zhangb
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 CNCwet 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 andmore 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 timewere favorable for solvent removal and the reduction of aerogel shrinking. The shrinkage increased the pore size inside the aerogel andmade 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 11.04MPa 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 387m2 g−1 and an average pore size of 7.2 nmusing 3.0% (w/w) CNC wet gel. © 2019 Society of Chemical Industry