Rheology of cellulose-[DBNH][CO2Et] solutions and shaping into aerogel beads†
Cellulose aerogel beads were made with JetCutting technology and dried by supercritical CO2 extraction. Ionic liquid, 1,5-diazabicyclo[4.3.0]non-5-enium propionate ([DBNH][CO2Et]), was shown to be a suitable solvent due to its rheological and thermodynamic properties. The flow and viscoelastic properties of cellulose-[DBNH][CO2Et] solutions were studied in detail as a function of polymer concentration and solution temperature and compared to those of cellulose-1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). [DBNH][CO2Et] is a thermodynamically better solvent as the cellulose intrinsic viscosity is more than two times higher than that in [Emim][OAc]. This allows to simultaneously fit (i) the processing window of JetCutter that requires rather low solution viscosity at high shear rates and (ii) cellulose concentration that is high enough above the overlap concentration to make intact aerogel beads. The beads were prepared from 2 and 3 wt% cellulose-[DBNH][CO2Et] solutions and coagulated in water, ethanol and isopropanol. Bead sizes were from 0.5 to 0.7 mm when made from 2% solutions and up to 1.8 mm when prepared from 3% solution. Cellulose aerogel beads prepared by JetCutting showed main characteristics similar to those of monolithic cellulose aerogels obtained from cellulose dissolved in other solvents: the specific surface area was 240–340 m2 g−1 at densities of 0.04–0.07 g cm−3.