Nanocellulose and Its Interface: On the Road to the Design of Emerging Materials

Abstract

The interest in the hierarchical structure, the multi-scale organization, and the properties of cellulose has long been the prerogative of botanists and plant physiologists. The last decade has witnessed the potential of a top-down approach to take apart cellulose-based raw materials into their micro-and nano-sized building blocks and to use them to design and fabricate functional materials and devices with new and, in some cases, outstanding properties. At present, cellulose is not only one of the main constituents of the plant and bacterial kingdom, it is also an important component of materials and manufactured goods, such as paper, textiles, or food additives. Depending on the extent of the scale down process, the fragments have variable size and in this review are collectively indicated as nanocellulose (NC). Although the interfacial properties of NC are always mentioned and recognized to contribute significantly to NC behavior, there is still room for reviewing the several recent reports highlighting the role of the interaction at the interface. In this scenario, the interface driven performances of some advanced NC-based materials are gaining in importance. This review aims at providing an overview of the most advanced of them, such as the Pickering emulsions, the supercapacitors, the drug crystallizing capsules, the nanowood.In nature, cellulose is synthesized by plants and also by some bacterial strains which can polymerize the glucose residues into linear β − 1, 4 −glucan chains. Once extracellularly secreted, the chains assemble, crystallize (the degree of crystallinity is up to 90%), and form nanostructures called bacterial nanocellulose (BNC) which in turn assemble forming microfibrils. Different from plant tissues where cellulose is embedded in a heterogeneous macrostructure, bacterial secretions are made of pure cellulose and are considered an excellent source of NC. [2] However, due to the large availability of cellulose from wood or other lowcost vegetable sources such as agriculture wastes, plant cellulose is the most common material for NC production. Several strategies for the preparation of NC have been reported. [3] A popular production route uses a pretreatment to introduce negative charges by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidation followed by a mechanical disintegration. [4] The behavior of NC has been largely studied, and it is well assessed that when NC colloidal suspensions are dried, they form flexible and transparent films with multifunctional properties. [5] These properties, first of all, depend on the degree of fibrillation of the colloidal NC. [6] Conversely, in aqueous solutions, NC Nanocellulose has several unique properties that render it a versatile mate rial with possible uses in a broad spectrum of applications. Nanocellulose is proved to form stable colloidal suspensions with interesting rheological properties, assemble in soft hydrogels of tunable porosity, compact dried films. Suggested or already current applications of these systems are in the f...

Understanding Nanocellulose–Water Interactions: Turning a Detriment into an Asset

“…The accessibility of cellulose chains to water is governed by the availability of hydroxy groups on the surface of a cellulose crystal. While cellulose–cellulose hydrogen bonds often take precedence over cellulose–water hydrogen bonds (hence the insolubility of cellulose in water), there is also an abundance of hydroxy groups on the crystallite surface that have the propensity to hydrogen bond with water . A common method by which to quantify the availability of hydroxy groups in cellulosic materials is to substitute the hydrogen in available hydroxy groups for deuterium through a water/deuterium oxide (H–D) solvent exchange .…”

“…While cellulose−cellulose hydrogen bonds often take precedence over cellulose−water hydrogen bonds (hence the insolubility of cellulose in water), there is also an abundance of hydroxy groups on the crystallite surface that have the propensity to hydrogen bond with water. 201 A common method by which to quantify the availability of hydroxy groups in cellulosic materials is to substitute the hydrogen in available hydroxy groups for deuterium through a water/deuterium oxide (H−D) solvent exchange. 202 The availability of hydroxy groups for solvent exchange is dependent on a number of factors: (i) their position in the cellulose chain (i.e., 2-, 3-, or 6-position), (ii) whether they are within the ordered or disordered region of the cellulose microfibril, and (iii) whether they are located on the surface or embedded within the crystallite (microfibril).…”

Does It Bind? A Method to Determine the Affinity of Calcium and Magnesium Ions for Polymers Using 1H NMR Spectroscopy

“…14 We note that the nature of CNC surfaces is currently an active area of research. 32 A strong affinity of Mg 2+ and Ca 2+ for carboxylatefunctionalized CNCs was observed by Lombardo et al, 33 who studied the salt-induced aggregation of CNCs prepared via TEMPO-mediated oxidation. These authors found that the critical concentrations of MgCl 2 and CaCl 2 required to induce aggregation of the CNCs were the same within experimental error.…”

“…Site-specific binding to the citrate moiety may also take place . We note that the nature of CNC surfaces is currently an active area of research …”

Naturally Derived Janus Cellulose Nanomaterials: Anisotropic Cellulose Nanomaterial Building Blocks and Their Assembly into Asymmetric Structures

“…(c2, c5) Janus CNM particles with more hydrophobicity (water contact angle is >90°) will sink more into the oil phase. Reprinted with permission under a Creative Commons Attribution Attribution-NonCommercial 4.0 International License from ref . Copyright 2021 Wiley-VCH.…”