Holocellulose Nanofibers of High Molar Mass and Small Diameter for High-Strength Nanopaper.

Wood cellulose nanofibers (CNFs) based on bleached pulp are different from the cellulose microfibrils in the plant cell wall in terms of larger diameter, lower cellulose molar mass, and modified cellulose topochemistry. Also, CNF isolation often requires high-energy mechanical disintegration. Here, a new type of CNFs is reported based on a mild peracetic acid delignification process for spruce and aspen fibers, followed by low-energy mechanical disintegration. Resulting CNFs are characterized with respect to geometry (AFM, TEM), molar mass (SEC), and polysaccharide composition. Cellulose nanopaper films are prepared by filtration and characterized by UV-vis spectrometry for optical transparency and uniaxial tensile tests. These CNFs are unique in terms of high molar mass and cellulose-hemicellulose core-shell structure. Furthermore, the corresponding nanopaper structures exhibit exceptionally high optical transparency and the highest mechanical properties reported for comparable CNF nanopaper structures.

High-performance and moisture-stable cellulose-starch nanocomposites based on bioinspired core-shell nanofibers.

Moisture stability and brittleness are challenges for plant fiber biocomposites intended for load-bearing applications, for instance those based on an amylopectin-rich (AP) starch matrix. Core-shell amylopectin-coated cellulose nanofibers and nanocomposites are prepared to investigate effects from the distribution of AP matrix. The core-shell nanocomposites are compared with nanocomposites with more irregular amylopectin (AP) distribution. Colloidal properties (DLS), AP adsorption, nanofiber dimensions (atomic force microscopy), and nanocomposite structure (transmission electron microscopy) are analyzed. Tensile tests are performed at different moisture contents. The core-shell nanofibers result in exceptionally moisture stable, ductile, and strong nanocomposites, much superior to reference CNF/AP nanocomposites with more irregular AP distribution. The reduction in AP properties is less pronounced as the AP forms a favorable interphase around individual CNF nanofibers.

Strong and moldable cellulose magnets with high ferrite nanoparticle content.

A major limitation in the development of highly functional hybrid nanocomposites is brittleness and low tensile strength at high inorganic nanoparticle content. Herein, cellulose nanofibers were extracted from wood and individually decorated with cobalt-ferrite nanoparticles and then for the first time molded at low temperature (<120 °C) into magnetic nanocomposites with up to 93 wt % inorganic content. The material structure was characterized by TEM and FE-SEM and mechanically tested as compression molded samples. The obtained porous magnetic sheets were further impregnated with a thermosetting epoxy resin, which improved the load-bearing functions of ferrite and cellulose material. A nanocomposite with 70 wt % ferrite, 20 wt % cellulose nanofibers, and 10 wt % epoxy showed a modulus of 12.6 GPa, a tensile strength of 97 MPa, and a strain at failure of ca. 4%. Magnetic characterization was performed in a vibrating sample magnetometer, which showed that the coercivity was unaffected and that the saturation magnetization was in proportion with the ferrite content. The used ferrite, CoFe2O4, is a magnetically hard material, demonstrated by that the composite material behaved as a traditional permanent magnet. The presented processing route is easily adaptable to prepare millimeter-thick and moldable magnetic objects. This suggests that the processing method has the potential to be scaled-up for industrial use for the preparation of a new subcategory of magnetic, low-cost, and moldable objects based on cellulose nanofibers.