Papers Proceedings »
Characterization and Modification of a Cellulose II Gel
This work focuses on a novel nanomaterial from the cellulose II allomorph, i.e. a cellulose II gel obtained out of the lyocell process; its first-time in-depth physicochemical characterization and novel ways for chemical modification. In comparison to native cellulose nanofibrils, this gel is produced with much higher energy-efficiency from a precursor obtained directly out of the lyocell process. The resulting cellulose II gel is composed of individual particles forming particle-like aggregates with a uniform nanostructure consisting of nanofibrils of 40-60 nm diameter. A water-redispersible gel was obtained according to a new drying protocol, based on simple oven drying in the presence of negatively charged polysaccharides. Furthermore, the gel was used as precursor to produce highly porous aerogels with a specific surface area of up to 423 m2/g featuring low thermal conductivity, low bulk density and high acoustic absorption at low frequencies. Modification of the never-dired cellulose II gel by introduction of negative carboxylate groups reduced the interaction between individual particles and caused the formation of individual spherical nanoparticles. Dependent on the amount of introduced charges, the particle size was tuned from a mean diameter of 73 nm to 129 nm. These spherical particles featured in contrast to cellulose nanocrystals an accessible amorphous region and can be easily redispersed in water after drying. A novel, straightforward and generally applicable functionalization strategy was established to introduce chemical anchor groups onto never-dried cellulosic surfaces. Based on this aqueous silanization protocol, never-dried nanocelluloses were decorated with azido, thiol and vinyl groups and the resulting functional materials were successfully post-modified by click chemistry approaches. In summary, the economic and straightforward production of this gel, its high surface area and porosity, the possibility to influence its particle size and to derivatize it in non-dried form; make it a promising contribution to the family of nanocelluloses with lots of scientifically interesting and economically feasible future applications.