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      Current characterization methods for cellulose nanomaterials

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      Chemical Society Reviews
      Royal Society of Chemistry (RSC)

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          Abstract

          Reliable characterization of cellulose nanomaterials is critical for their utilization in various applications.

          Abstract

          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.

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          DLS and zeta potential - What they are and what they are not?

          Adequate characterization of NPs (nanoparticles) is of paramount importance to develop well defined nanoformulations of therapeutic relevance. Determination of particle size and surface charge of NPs are indispensable for proper characterization of NPs. DLS (dynamic light scattering) and ZP (zeta potential) measurements have gained popularity as simple, easy and reproducible tools to ascertain particle size and surface charge. Unfortunately, on practical grounds plenty of challenges exist regarding these two techniques including inadequate understanding of the operating principles and dealing with critical issues like sample preparation and interpretation of the data. As both DLS and ZP have emerged from the realms of physical colloid chemistry - it is difficult for researchers engaged in nanomedicine research to master these two techniques. Additionally, there is little literature available in drug delivery research which offers a simple, concise account on these techniques. This review tries to address this issue while providing the fundamental principles of these techniques, summarizing the core mathematical principles and offering practical guidelines on tackling commonly encountered problems while running DLS and ZP measurements. Finally, the review tries to analyze the relevance of these two techniques from translatory perspective.
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            Cellulose nanofibers prepared by TEMPO-mediated oxidation of native cellulose.

            Never-dried and once-dried hardwood celluloses were oxidized by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated system, and highly crystalline and individualized cellulose nanofibers, dispersed in water, were prepared by mechanical treatment of the oxidized cellulose/water slurries. When carboxylate contents formed from the primary hydroxyl groups of the celluloses reached approximately 1.5 mmol/g, the oxidized cellulose/water slurries were mostly converted to transparent and highly viscous dispersions by mechanical treatment. Transmission electron microscopic observation showed that the dispersions consisted of individualized cellulose nanofibers 3-4 nm in width and a few microns in length. No intrinsic differences between never-dried and once-dried celluloses were found for preparing the dispersion, as long as carboxylate contents in the TEMPO-oxidized celluloses reached approximately 1.5 mmol/g. Changes in viscosity of the dispersions during the mechanical treatment corresponded with those in the dispersed states of the cellulose nanofibers in water.
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              Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance

              Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
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                Author and article information

                Journal
                CSRVBR
                Chemical Society Reviews
                Chem. Soc. Rev.
                Royal Society of Chemistry (RSC)
                0306-0012
                1460-4744
                2018
                2018
                : 47
                : 8
                : 2609-2679
                Affiliations
                [1 ]Department of Materials Science and Engineering
                [2 ]Blacksburg
                [3 ]USA
                [4 ]US Forest Service, Forest Products Laboratory
                [5 ]Madison
                [6 ]Department of Chemical Engineering
                [7 ]Université Grenoble Alpes
                [8 ]Laboratory of Pulp and Paper Science and Graphic Arts (LGP2)
                [9 ]CNRS
                [10 ]F-38000 Grenoble
                [11 ]France
                [12 ]MERLN Institute for Technology-inspired Regenerative Medicine
                [13 ]Complex Tissue Regeneration
                [14 ]Department
                [15 ]Maastricht University
                [16 ]MD
                [17 ]In Vitro Toxicology Group
                [18 ]Institute of Life Science
                [19 ]Centre for NanoHealth
                [20 ]Swansea University Medical School
                [21 ]Swansea, SA2 8PP
                [22 ]Department of Chemical Engineering, McMaster University, Hamilton
                [23 ]Ontario
                [24 ]Canada
                [25 ]The Bristol Composites Institute (ACCIS)
                [26 ]University Walk
                [27 ]University of Bristol
                [28 ]Bristol
                [29 ]UK
                [30 ]Department of Chemistry
                [31 ]American University
                [32 ]Washington
                [33 ]FPInnovations
                [34 ]Vancouver
                [35 ]University Grenoble Alpes
                [36 ]CERMAV
                [37 ]38000 Grenoble
                [38 ]School of Materials Engineering
                [39 ]Purdue University
                [40 ]West Lafayette
                [41 ]USDA Forest Service Headquarters
                [42 ]R&D Deputy Area
                [43 ]Washington DC
                [44 ]Vireo Advisors
                [45 ]Boston
                [46 ]Department of Wood Science
                [47 ]University of British Columbia
                [48 ]Department of Forestry
                [49 ]Oregon State University
                [50 ]College of Engineering
                [51 ]Maths and Physical Sciences
                [52 ]University of Exeter
                Article
                10.1039/C6CS00895J
                30fd62a8-63e4-476d-8589-27e4214f1d5d
                © 2018

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                Self URI (article page): http://xlink.rsc.org/?DOI=C6CS00895J

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