Aerogel-like (low density and high surface area) cellulose monoliths and beads obtained without supercritical- or freeze-drying

Aerogels are lightweight open-pore nanostructured materials with high specific surface area. Till now, to obtain cellulose II aerogels, drying with supercritical CO2 was applied to preserve network morphology during drying and keep porosity open. In this work, we demonstrate that if dissolving cellulose in aqueous NaOH (with or without additive ZnO) and coagulating in ethanol and drying by evaporation in low vacuum from ethanol, cellulose II aerogel-like materials are obtained. In other words, hornification due to drying was avoided. No cellulose chemical modification or crosslinking was performed. Cellulose monoliths (after gelation of solutions) and beads (no gelation) with density 0.15-0.25 g/cm(3) and specific surface area up to 250 m(2)/g were obtained avoiding using high-pressure (drying in supercritical conditions) or low-pressure (freeze-drying) technology. This discovery opens a new way of making meso- and small macroporous cellulose materials. In order to explore this phenomenon, various process parameters were tested. Other than ethanol cellulose non-solvents were probed, such as water, HCl, acetone and isopropanol. The influence of ZnO concentration and aging time of cellulose/NaOH/water gels on dry material properties was investigated. It was demonstrated that gelation step is not required to obtain aerogel-like cellulose as beads were made by dropping non-gelled cellulose/NaOH/water solution in ethanol. The hypotheses on the absence pores' collapse during evaporative drying were suggested.

Automated summary

Cellulose II aerogel-like materials can be obtained by dissolving cellulose in aqueous NaOH and drying by evaporation in low vacuum from ethanol, avoiding hornification due to drying. This discovery opens up a new way of making meso- and small macroporous cellulose materials.