A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique combination of characteristics, such as high on-axis stiffness, sustainability, scalability, and mechanical reinforcement of a wide variety of materials, leading to their utility across a broad spectrum of high-performance material applications. However, with this exponential growth in interest/activity, the development of measurement protocols necessary for consistent, reliable and accurate materials characterization has been outpaced. These protocols, developed in the broader research community, are critical for the advancement in understanding, process optimization, and utilization of CNMs in materials development. This review establishes detailed best practices, methods and techniques for characterizing CNM particle morphology, surface chemistry, surface charge, purity, crystallinity, rheological properties, mechanical properties, and toxicity for two distinct forms of CNMs: cellulose nanocrystals and cellulose nanofibrils.

The grafting of thermosensitive amine-terminated statistical polymers onto the surface of cellulose nanocrystals (CNCs) was achieved by a peptidic coupling reaction, leading to unusual properties like colloidal stability at high ionic strength, surface activity, and thermoreversible aggregation. We have used a large variety of experimental techniques to investigate the properties of the polymer-decorated CNCs at different length-scales and as a function of the different reaction parameters. A high grafting density could be obtained when the reaction was performed in DMF rather than water. Infrared and solid-state NMR spectroscopy data unambiguously demonstrated the covalent character of the bonding between the CNCs and the macromolecules, whereas TEM images showed a preserved individualized character of the modified objects. Dynamic light scattering and zeta potential measurements were also consistent with individual nanocrystals decorated by a shell of polymer chains. Surface tension measurements revealed that CNCs became surface-active after the grafting of thermosensitive amines. Decorated CNCs were also stable against high electrolyte concentrations. A thermoreversible aggregation was also observed, which paves the way for the design of stimuli-responsive biobased nanocomposite materials.

Cellulose nanocrystal suspensions in apolar solvent spontaneously form iridescent liquid-crystalline phases but the control of their macroscopic order is usually poor. The use of electric fields can provide control on the cholesteric orientation and its periodicity, allowing macroscopic sample homogeneity and dynamical tuning of their iridescent hues, and is demonstrated here.