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.

Cellulose nanofibrils (CNF) are usually obtained by breaking down the lignocellulosic structure of pulp, i.e., as cellulose I allomorph and according to rather energy-intensive pathways. In contrast to those approaches, TENCEL gel is obtained from a nonfibrous cellulose II precursor directly out of the Lyocell process in a deceptively energy-efficient way: After enzymatic treatment and only one cycle in a high-pressure homogenizer (comparing to up to 20 cycles for CNF manufacture) the final gel is obtained. The utilization of a starting material from an already existing industrial process is another distinct advantage. This novel cellulose II gel possesses a particle-like, homogeneous morphology and is composed of individual particles with a size of less than one micron, featuring the rheological behavior of a soft solid. The course of the gel production process was studied with respect to changes in crystallinity, appearance and molecular weight, whereas the morphology and size of the final gel particles were assessed comprehensively by light-microscopy, dynamic light scattering and electron microscopy. In water, the individual particles form aggregates with a mean size of 11 μm. The viscoelastic gel forms highly porous cryogels with a surface area of 298 m2/g and a well-defined nanostructure. These features were studied in depth by SAXS, nitrogen sorption experiments and SEM. The economic production in combination with the highly accessible surface offers unique properties, and applications are envisioned as tailored, high performance materials.

Cellulose II gels from a stream of the Lyocell fiber process were transformed into spherical nanoparticles by carboxymethylation and subsequent homogenization.

Cellulose II nanospheres with a soft, amorphous outer shell are synthesized and characterized to show their structure–property relationship.

Recently, a new member of the nanocellulose family was introduced, a cellulose II gel consisting of nanostructured and spherical particles. In this study, we compared two different drying techniques to obtain highly porous powders from this gel with preserved meso-and macroporous nanostructure: first, freeze-drying after solvent exchange to tBuOH and second, supercritical drying of the respective EtOH alcogel. The approaches yielded aerogel powders with surface areas of 298 and 423 m 2 /g, respectively. Both powders are amphiphilic and possess energetically heterogeneous surfaces with dominating dispersive term of the surface energy in the range of 50-52 mJ/m 2 , as determined by a combination of physicochemical surface characterization techniques, such as iGC, BET and SEM. Despite the lower surface area, the cheaper and more widespread method, freeze-drying, yields a more polar and reactive cryogel.Keywords Nanocellulose Á Lyocell Á Inverse gas chromatography Á Thermoporosimetry Á Freezedrying Á Supercritical drying Abbreviations CNFCellulose nanofibrils FD Freeze-drying scCO 2 Supercritical CO 2 Electronic supplementary material The online version of this article