Linear correlation between specific surface and grafting density of tunable aerogels of microfibrillated cellulose from
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ORIGINAL RESEARCH
Linear correlation between specific surface and grafting density of tunable aerogels of microfibrillated cellulose from different origins Emilie Ressouche . Sonia Molina-Boisseau . Karim Mazeau . David Gue´rin . Matthieu Schelcher . Laurent Heux
Received: 22 January 2020 / Accepted: 25 June 2020 Ó Springer Nature B.V. 2020
Abstract Cellulose aerogels with variable specific surface areas were prepared by freeze-drying cellulose microfibrillar suspensions dispersed in mixtures of water and tert-butyl alcohol (TBA). Varying the composition of solvent used for the suspensions and the origin and composition of the microfibrils allowed to extensively tune the specific surface area of these aerogels, with values ranging from 32 to 280 m2/g. Depending on the solvent mixture composition, these aerogels presented substantial morphological differences, attributed to the templating power of the various crystals obtained during the freezing of the solvent mixtures. The aerogels were hydrophobized with sebacoyl chloride in a gas-phase reaction operated under conditions of either full or partial Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03319-y) contains supplementary material, which is available to authorized users. E. Ressouche S. Molina-Boisseau K. Mazeau L. Heux (&) CNRS, CERMAV, Univ. Grenoble Alpes, 38000 Grenoble, France e-mail: [email protected] Present Address: E. Ressouche Department of Applied Physics, Aalto University, P.O. Box 15100, 02150 Espoo, Finland D. Gue´rin M. Schelcher Centre Technique du Papier, 38044 Grenoble, France
derivatization of the accessible surface. For fully grafted specimens, a linear correlation could be established between the overall degree of substitution of the grafted samples and the specific surface area of the aerogels before grafting. From the slope of this correlation line, an average number of grafted molecules per surface area of approximately 3 molecules/nm2 could be calculated. Atomic-scale models gave a plausible overview of the full surface coverage of the aerogel microfibrils in good agreement with the experimental data. Contact angle measurements confirmed the hydrophobicity of the grafted aerogels, as well as the presence of heterogeneities for the partially grafted samples. Keywords Cellulose microfibrils Aerogels Surface modification Gas-phase CP-MAS NMR Hydrophobization
Introduction In a seminal half a page paper, Kistler (1931) initially described how the inner structure of gels could be preserved by critical point drying, leading according to him, to a ‘‘coherent aerogel of unchanged volume’’. First developed for silica, it was soon found that the technique could be extended to a host of inorganic and organic gels and at present there seems to be no limit to
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Cellulose
the number of aerogels that can be produced with such a technique. In common, all the aerogels share very unique properties ranging from low
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