Cellulosic aerogels as ultra-lightweight materials. Part 2: Synthesis and properties 2^nd ICC 2007, Tokyo, Japan, October 25–29, 2007

Abstract

Ultra-lightweight cellulose aerogels can be obtained in three steps: (1) preparation of a cellulose solution in molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) at 110–120°C and casting of the viscous mass into moulds; (2) extraction of the solidified castings with ethanol to initiate cellulose aggregation and to remove NMMO·H2O so that the fragile, fine-porous texture of cellulose II is largely retained; and (3) drying of the lyogel using supercritical carbon dioxide (scCO2). According to this approach, cellulosic aerogels were prepared from eight commercial cellulosic materials and pulps and analysed for selected chemical, physicochemical and mechanical parameters. The results reveal that all aerogels obtained from 3% cellulose containing NMMO·H2O melts had a largely uniform mesoporous structure with an average pore size of ∼9–12 nm, surface area of 190–310 m2 g-1, and specific density of 0.046–0.069 g cm-3, but rather low mechanical stability expressed as compressive yield strain of 2.9–5.5%. All samples showed viscoelastic behaviour, with Young's modulus ranging from ∼5 to 10 N mm-2. Doubling the cellulose content in the NMMO·H2O melt from 3% to 6% increased Young's modulus by one order of magnitude. Shrinkage of the fragile cellulose bodies during scCO2 drying was still considerable and is subject to further investigations. Influencing parameters such as scCO2 pressure, cellulose content, regenerating solvent and the number of regenerating baths were optimised.

Super water absorbing and shape memory nanocellulose aerogels from TEMPO-oxidized cellulose nanofibrils via cyclic freezing–thawing

“…Cellulose aerogels can be fabricated from either homogeneous cellulose solutions [18][19][20][21][22][23][24][25] or heterogeneous aqueous nanocellulose suspensions. 4,7,11,13,[26][27][28][29][30][31][32][33][34] Aerogels prepared from cellulose solutions require lengthy, multiple steps of dissolving cellulose in solvents, such as alkali hydroxide/urea solution, 18 calcium thiocyanate tetrahydrate, 19 N-methyl-morpholine-N-oxide, 20,21 sodium hydroxide, 22 lithium chloride/dimethylacetamine, 23 lithium chloride/dimethyl sulfoxide 24 and ionic liquid, 25 followed by induced gelation, solvent exchange and supercritical or freeze drying.…”

Aerocellulose based on all‐cellulose composites

“…The nature of the phase transformations during partial dissolution of MCC in 8 wt % LiCl/DMAc has been previously analyzed by wide-angle X-ray scattering (WAXS) and 13 C solid-state NMR. 21 Partial dissolution of Avicel MCC involves the removal of sheets of cellulose from the surface of the initial cellulose I crystallites of the MCC.…”

“…9,10 Another possible route involves the dissolution of cellulose in hydrated Nmethylmorpholine N-oxide (NMMO) followed by a solvent exchange procedure involving heptane, water, acetone, methanol, or ethanol. 6,13,14 Aerogels made of native cellulose dissolved in sodium hydroxide have also been reported. 12 Recently, two cellulose aerogels were prepared by dissolution of cellulose or lignocellulosic materials in ionic liquids.…”

“…12 Recently, two cellulose aerogels were prepared by dissolution of cellulose or lignocellulosic materials in ionic liquids. 15,16 The final step in the preparation of an aerogel involves freeze-drying, 9,10 supercritical drying, 6,9,[12][13][14][15][16] and sometimes drying by evaporation.…”

Transparent Aerogels with High Mechanical Strength Composed of Cellulose-silica Cross-linked networks

“…One solution is to fabricate cellulose aerogels [16][17][18][19] with interconnected open-porous network structures. However, they re light-tight, and the preparation process usually involves the utilization of toxic isocyanates.…”