Periodate oxidation of cellulose can be an intriguing alternative to TEMPO mediated oxidation since periodate can be recovered and regenerated. In continuation of our previous work on preparation of birefringent, transparent aerogels from TEMPO-oxidized, nanofibrillated pulp, this study investigates the manufacture of cellulosic aerogels from 2,3-dicarboxyl cellulose (DCC) as obtained by consecutive treatment of dissolving pulp with periodate and chlorite in aqueous medium. Subsequent mechanical fibrillation of the oxidized pulp (1 mmol g–1 COO–, conductometric titration) afforded individualized DCC fibrils (nf–DCC) with uniform dimensions (AFM: diameter 2.08 ± 0.4 nm, n=35; length 525 ± 160 nm, n=8). Acid-induced gelation of aqueous dispersions of nf–DCC afforded nematic aquogels. After replacement of interstitial water by ethanol and subsequent scCO2 drying (95 MPa, 40 °C), highly transparent aerogels of well-preserved nematic ordering were obtained. The self-aligned structure dominating the morphology of nf–DCC aerogels was unveiled by FEG-SEM imaging and was quantified by polarized light experiments using the modified Michel–Lévi chart. The calculated birefringence was about 1.75 x 10–4 for aerogels of a density of 19 mg cm–3. The prepared nf–DCC aerogels featured furthermore comparatively high internal surfaces of up to 500 m2 g–1, high transparency in the visible light range (~70% transmission at 600 nm for a 1 mm thick samples with a density of 25 mg cm–3) and specific moduli of around 9 MPa cm3 g–1 which renders them interesting materials for high performance insulation and optical applications. In an attempt to improve the rather poor mechanical properties inherent to lightweight cellulosic aerogels, post-scCO2-drying uniaxial-densification has been found to be a very surprisingly efficient means of strain-hardening and pore-size control as entirely mesoporous and mechanical strong nanocellulose aerogels at full preservation of nematic ordering, birefringence and transparence can be obtained.

2,3-Dicarboxyl nano cellulose: A novel source material for transparent, birefringent and thermally superinsulating aerogels

253rd National Meeting (2017)

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