Fine-fibrous cellulose II aerogels of high specific surface from pulp solutions in TBAF·H2O/DMSO

Abstract

Abstract Lightweight cellulose II aerogels featuring densities of about 40–70 mg cm−3 were prepared from 1 to 3% solutions of different pulps in hot (60°C) tetra-n-butylammonium fluoride (TBAF)·H2O/dimethyl sulfoxide (DMSO) by (i) the coagulation of cellulose with EtOH to afford self-standing, transparent and homogeneous gels, (ii) gel ripening and washing, (iii) solvent exchange and (iv) supercritical carbon dioxide (scCO2) drying. Size exclusion chromatography (SEC) analyses confirmed that the chemical integrity of cellulose is largely preserved at short dissolution times. Dissolution of more than 2% of cellulose at a sufficiently low viscosity for solution, casting was achieved after the water content of TBAF was reduced to a value equaling that of the monohydrate. Intriguingly, the obtained aerogels featured higher specific surfaces (≤470 m2 g−1) than comparable materials prepared from other cellulose solvents. This is due to the particular morphology of TBAF aerogels, which is supposedly formed by spinodal decomposition of the cellulose/solvent mixture upon exposure to the cellulose antisolvent. As a result, largely homogeneous three-dimensional (3D) networks of agglomerated cellulose spheres were formed, which simultaneously acted as supporting scaffolds for interconnected micron-size voids. As cellulose spheres are composed of very small interwoven nanofibers, TBAF-derived aerogels contain a high portion of micropores and small amounts of mesopores, too.