Cellulose fibrils with widths in the nanometer range are nature-based materials with unique and potentially useful features. Most importantly, these novel nanocelluloses open up the strongly expanding fields of sustainable materials and nanocomposites, as well as medical and life-science devices, to the natural polymer cellulose. The nanodimensions of the structural elements result in a high surface area and hence the powerful interaction of these celluloses with surrounding species, such as water, organic and polymeric compounds, nanoparticles, and living cells. This Review assembles the current knowledge on the isolation of microfibrillated cellulose from wood and its application in nanocomposites; the preparation of nanocrystalline cellulose and its use as a reinforcing agent; and the biofabrication of bacterial nanocellulose, as well as its evaluation as a biomaterial for medical implants.

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Cellulosefibrillen und ‐kristalle mit einem Durchmesser im Nanometerbereich sind naturbasierte Materialien mit einzigartigen und potenziell wertvollen Eigenschaften. Vor allem eröffnen diese neuartigen Nanocellulosen dem natürlichen Polymer Cellulose die stark expandierenden Einsatzgebiete nachhaltige Materialien, Nanokomposite sowie Produkte für die Medizin und die Lebenswissenschaften. Die Nanodimensionen der Strukturelemente führen zu großen Oberflächen und damit zu starken Wechselwirkungen dieser Cellulosen mit umgebenden Stoffen wie Wasser, anorganischen, organischen und polymeren Verbindungen, Nanopartikeln und lebenden Zellen. Diese Übersicht bietet das aktuelle Wissen über die Isolierung mikrofibrillierter Cellulose aus Holz und ihre Anwendung in Nanokompositen, die Herstellung nanokristalliner Cellulose und ihren Einsatz als Verstärkungsmaterial sowie die biotechnologische Erzeugung bakterieller Nanocellulose einschließlich ihrer Eignung als Biomaterial für medizinische Implantate.

Gold nanoparticles of 5 nm diameter, stabilized by 4-(dimethylamino)pyridine (DMAP), were coated with poly(sodium 4-styrene sulfonate) (PSS) via electrostatic self-assembly. The suspension stability, monitored by the gold surface plasmon band (SPB), was studied by varying the pH, the PSS chain length, and PSS concentration. Enhanced stability is obtained at pH 10 (above the pKa of DMAP) when the polymer chain length matches or exceeds the particle circumference. Solid state 13C NMR was used to determine the presence of DMAP and polymers after subsequent deposition of weak and strong polycations: poly(allylamine hydrochloride) (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC). At pH 10, DMAP remains associated with the nanoparticle after the first PSS layer has been formed. When PAH or PDADMAC are subsequently added at pH 4.5, DMAP is expelled, the suspensions remain stable, and zeta potential values indicate complete charge reversal. In the case of PDADMAC, however, the first layer of PSS is not fully retained. When PDADMAC is added at pH 10, DMAP and the first PSS layer are retained but lower zeta potentials and a higher SPB shift indicate a degraded stability. For PAH addition at pH 9.5, both DMAP and PSS are expelled and the suspension becomes unstable. These differences in stability of the multilayer components and the nanoparticle suspension are rationalized in terms of chain flexibility, polymer charge density, and the ability of the polymer functional groups to directly interact with the gold surface.

In this study, four-layer stacks of bleached, unrefined Kraft papers are exposed to a plane-to-plane dielectric barrier discharge at atmospheric pressure operated in a glow-like discharge regime and sustained in a mixture of hexamethyldisiloxane and helium gases. Scanning electron microscopy confirms that the plasma-deposited coating follows the roughness of the porous cellulosic substrate. Whereas fairly spatially homogeneous coatings are obtained on silicon, significant variations of the coatings' thickness, organic content, and water contact angle are observed along the gas flow lines on the Kraft paper. These effects are even more important in the presence of substrate outgassing. In addition, plasma-generated species sequentially penetrate down to the fourth layer of the cellulosic substrate, rendering surfaces hydrophobic with very low water absorption kinetics.