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Molecules 2018, 23(6), 1427; https://doi.org/10.3390/molecules23061427

A General Aqueous Silanization Protocol to Introduce Vinyl, Mercapto or Azido Functionalities onto Cellulose Fibers and Nanocelluloses

1
Department of Chemistry, Division of Chemistry of Renewable Resources, University of Natural Resources and Life Sciences Vienna (BOKU), Konrad-Lorenz-Straße 24, A-3430 Tulln, Austria
2
Lenzing AG, 4860 Lenzing, Austria
3
Department of Materials Science and Process Engineering, Institute of Wood Technology and Renewable Materials, University of Natural Resources and Life Sciences Vienna (BOKU), A-3430 Tulln, Austria
4
Johan Gadolin Process Chemistry Centre, Åbo Akademi University, FI-20500 Åbo/Turku, Finland
*
Authors to whom correspondence should be addressed.
Received: 16 May 2018 / Revised: 4 June 2018 / Accepted: 5 June 2018 / Published: 12 June 2018
(This article belongs to the Special Issue The Future for Cellulose Nanomaterials)
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Abstract

The effective and straight-forward modification of nanostructured celluloses under aqueous conditions or as “never-dried” materials is challenging. We report a silanization protocol in water using catalytic amounts of hydrogen chloride and then sodium hydroxide in a two-step protocol. The acidic step hydrolyzes the alkoxysilane to obtain water-soluble silanols and the subsequent addition of catalytic amounts of NaOH induces a covalent reaction between cellulose surficial hydroxyl groups and the respective silanols. The developed protocol enables the incorporation of vinyl, thiol, and azido groups onto cellulose fibers and cellulose nanofibrils. In contrast to conventional methods, no curing or solvent-exchange is necessary, thereby the functionalized celluloses remain never-dried, and no agglomeration or hornification occurs in the process. The successful modification was proven by solid state NMR, ATR-IR, and EDX spectroscopy. In addition, the covalent nature of this bonding was shown by gel permeation chromatography of polyethylene glycol grafted nanofibrils. By varying the amount of silane agents or the reaction time, the silane loading could be tuned up to an amount of 1.2 mmol/g. Multifunctional materials were obtained either by prior carboxymethylation and subsequent silanization; or by simultaneously incorporating both vinyl and azido groups. The protocol reported here is an easy, general, and straight-forward avenue for introduction of anchor groups onto the surface of never-dried celluloses, ready for click chemistry post-modification, to obtain multifunctional cellulose substrates for high-value applications. View Full-Text
Keywords: aqueous silanization; click chemistry; cellulose nanofibrils; nanocellulose; cellulose II gel; green chemistry; cellulose modification aqueous silanization; click chemistry; cellulose nanofibrils; nanocellulose; cellulose II gel; green chemistry; cellulose modification
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Beaumont, M.; Bacher, M.; Opietnik, M.; Gindl-Altmutter, W.; Potthast, A.; Rosenau, T. A General Aqueous Silanization Protocol to Introduce Vinyl, Mercapto or Azido Functionalities onto Cellulose Fibers and Nanocelluloses. Molecules 2018, 23, 1427.

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