Sylvain Galland

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.

Cellulose nanofibers decorated with magnetic nanoparticles – synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker

Magnetic nanoparticles are the functional component for magnetic membranes, but they are difficult to disperse and process into tough membranes. Here, cellulose nanofibers are decorated with magnetic ferrite nanoparticles formed in situ which ensures a uniform particle distribution, thereby avoiding the traditional mixing stage with the potential risk of particle agglomeration. The attachment of the particles to the nanofibrils is achieved via aqueous in situ hydrolysis of metal precursors onto the fibrils at temperatures below 100 °C. Metal adsorption and precursor quantification were carried out using Induction Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). FE-SEM was used for high resolution characterization of the decorated nanofibers and hybrid membranes, and TEM was used for nanoparticle size distribution studies. The decorated nanofibers form a hydrocolloid. Large (200 mm diameter) hybrid cellulose/ferrite membranes were prepared by simple filtration and drying of the colloidal suspension. The low-density, flexible and permanently magnetized membranes contain as much as 60 wt% uniformly dispersed nanoparticles (thermogravimetric analysis data). Hysteresis magnetization was measured by a Vibrating Sample Magnetometer; the inorganic phase was characterized by XRD. Membrane mechanical properties were measured in uniaxial tension. An ultrathin prototype loudspeaker was made and its acoustic performance in terms of output sound pressure was characterized. A full spectrum of audible frequencies was resolved.

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.

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.

Influence of processing routes on morphology and low strain stiffness of polymer/nanofibrillated cellulose composites

Abstract The morphology of polymer/nanofibrillated cellulose (NFC) composite sheets produced using different techniques and its influence on low strain stiffness were assessed by optical and transmission electron microscopy. Solvent processing led to relatively homogeneous NFC dispersions and significant reinforcement of the in-plane Young’s modulus. The continuous cellular networks obtained by wet comingling of polylactide powder or latex with NFC also provided efficient and essentially scale independent reinforcement, in spite of the extensive agglomeration of the NFC. However, the irreversible nature of these networks is incompatible with low pressure thermoplastic processing routes such as physical foaming, and while they may be broken up by e.g. extrusion, this led to substantial loss in reinforcement, particularly at temperatures above the glass transition temperature of the matrix, consistent with the observation of isolated low aspect ratio NFC aggregates in the extruded specimens.

Elastic properties of cellulose nanopaper versus conventional paper

INTRODUCTION The creep rate of some hygroscopic materials has a strong dependence on fluctuations in the ambient relative humidity (RH). Wood [1], paper [2] and individual wood fibers [3] are known examples. This phenomenon, known as mechanosorptive creep, threatens the integrity of any hygroscopic material structure under constant load, and particularly shortens the storage-life of corrugated boxes [4]. Previously, many models for describing the generic mechanisms of mechanosorptive creep, as well as mechanisms particular to paper, have been proposed. Mechanosorptive creep in cellulosebased materials has been attributed to physical ageing of glassy materials [5], macroscopic moisture gradients and associated enhanced stresses [6], various fiber-level processes introducing stress concentrations [7,8,9] and more [6,10]. This work is focused on testing the predictions of the previously proposed models, and particularly identifying the length-scale at which the dominant mechanosorptive creep mechanism is found; sample size-level, fibril-level, or subfibrillevel. To avoid the complexity of hierarchical microstructures typical to wood or paper, we use nanofibrillated cellulose (NFC) films and aerogels [11] as model systems.