The Colloidal Properties of Nanocellulose

Abstract

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

Amyloid fibril-nanocellulose interactions and self-assembly

“…The much higher exponent of 4.0 can be explained by the fact that the TO-CNF efficiently contribute to the elasticity of the system by forming a network. While CNCs are not able to form a network at the concentrations added in the experiment, the overlap concentration of TO-CNFs is in a concentration window where the formation of TO-CNF networks has been previously reported [28,57]. The exponent of 4.0 ± 0.1 lies in between theoretical exponents of 3.67 for the relevant concentration range [58] and experimental scaling exponents for TO-CNFs of 4.1 and 4.5, respectively [59,60].…”

“…To improve the mechanical properties of macroscopic amyloid materials, combinations of amyloid fibrils with polysaccharides [21] and with nanocelluloses [22,23] have been tested. Nanocelluloses are a class of bio-based and biodegradable materials with excellent mechanical properties and an immensely broad range of applications in functional materials [24][25][26][27][28]. The term ''nanocelluloses" encompasses cellulose nanofibrils (CNFs) containing disordered and crystalline regions and pure crystalline cellulose nanocrystals (CNCs) [29,30].…”

“…CNCs are commonly prepared from wood pulp or cotton by a sulfuric acid hydrolysis treatment that shortens the CNCs and introduces negatively charged sulfate half-ester groups [30]. The negative charge of chemically modified nanocelluloses (or other polysaccharides) and the pH-dependent positive charge of proteins are the basis for polyelectrolyte complexation, a common type of interaction between oppositely charged polymers [28,31,32]. Polyelectrolytes are surrounded by an electrical double layer, a cloud of tightly packed counter-ions with reduced translational entropy.…”

“…When complexes are formed through ionic bonds, the entropy of the polyelectrolytes is decreased, however the entropy of the system as a whole is increased due to the release of large amounts of counter-ions and bound water. Therefore, the driving force for complexation is the gain of entropy rather than short-ranged interactions between the polyelectrolytes [28,[32][33][34]. In the specific case of positively charged, native lysozyme adsorbing onto mechanically disintegrated CNFs, isothermal titration calorimetry (ITC) proved that the adsorption is entropy-driven and influenced by the protonation state of hemicelluloses remaining on the CNF surface [35].…”

Isotropic Gels of Cellulose Nanocrystals Grafted with Dialkyl Groups: Influence of Surface Group Topology from Nonlinear Oscillatory Shear

“…Over the past decades, assessing rheological properties has become an integral part of characterizing different forms of cellulose. Physicochemical properties of particles affect the rheological behavior of CNC suspensions . In general, depending on whether attractive or repulsive forces between CNCs dominate, aqueous CNC suspensions either form isotropic, biphasic (containing both liquid crystalline and isotropic domains), liquid crystalline, and repulsive glasses so-called phases or form isotropic suspensions, isotropic (attractive) gels .…”