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.

Nanostructural effects on polymer and water dynamics in cellulose biocomposites: (2)h and (13)c NMR relaxometry.

Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characterized separately. Nanocomposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolymer matrix are investigated at different hydration states. Films of XG, CNF, and CNF/XG composites are subjected to detailed (2)H and (13)C NMR relaxation studies. Since the (2)H NMR signal arises from heavy water and the (13)C signal from the polysaccharides, molecular water and polymer dynamics is for the first time investigated separately. In the neat components, (2)H transverse relaxation (T2) data are consistent with water clustering at the CNF fibril surfaces, but bulk spread of moisture in XG. The new method results in a description of water interaction with the nanoscale phases. At low hydration, water molecules at the CNF/XG interface exhibit higher water mobility than in neat CNF or XG, due to locally high water concentration. At the same time, CNF-associated interphase segments of XG show slower NMR-dynamics than that in neat XG.

Core-shell cellulose nanofibers for biocomposites - nanostructural effects in hydrated state.

Core-shell wood cellulose nanofibers (CNF) coated by an XG hemicellulose polymer are prepared and used to make biocomposites. CNF/XG biocomposites have interest as packaging materials and as hydrated CNF/XG plant cell wall analogues. Structure and properties are compared between Core-shell CNF/XG and more inhomogeneous CNF/XG. Experiments include XG sorption, dynamic light scattering of CNF nanoparticle suspensions, FE-SEM of nanostructure, moisture sorption, tensile testing in moist conditions and dynamic mechanical analysis. (2)H NMR relaxometry is performed on materials containing sorbed (2)H2O2 in order to assess water molecular dynamics in different materials. The results clarify the roles of CNF, XG and the CNF/XG interface in the biocomposites, both in terms of moisture sorption mechanisms and mechanical properties in moist state. The concept of core-shell nanofiber network biocomposites, prepared by filtering of colloids, provides improved control of polymer matrix distribution and interface structure. Also, present mechanical properties are much superior to comparable plant fiber biocomposites.

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.