Characterization challenges for a cellulose nanocrystal reference material: dispersion and particle size distributions
- 376 Downloads
Cellulose nanocrystals (CNCs) have high aspect ratios, polydisperse size distributions, and a strong propensity for aggregation, all of which make them a challenging material for detailed size and morphology characterization. A CNC reference material produced by sulfuric acid hydrolysis of softwood pulp was characterized using a combination of dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy, and X-ray diffraction. As a starting point, a dispersion protocol using ultrasonication was developed to provide CNC suspensions with reproducible size distributions as assessed by DLS. Tests of various methods for AFM sample preparation demonstrated that spin coating on a positively charged substrate maximizes the number of individual particles for size analysis, while minimizing the presence of agglomerates. The effects of sample-to-sample variability, analyst bias, and sonication on size distributions were assessed by AFM. The latter experiment indicated that dispersion of agglomerates by sonication did not significantly change the size distribution of individual CNCs in suspension. Comparison with TEM data demonstrated that the two microscopy methods provide similar results for CNC length (mean ~ 80 nm); however, the particle width as measured by TEM is approximately twice that of the CNC height (mean 3.5 nm) measured by AFM. The individual crystallite size measured by X-ray diffraction is intermediate between the two values, although closer to the AFM height, possibly indicating that laterally agglomerated CNCs contribute to the TEM width. Overall, this study provides detailed information that can be used to assess the factors that must be considered in measuring CNC size distributions, information that will be useful for benchmarking the performance of different industrially sourced materials.
KeywordsCellulose nanocrystals Dispersion Particle size distribution Atomic force microscopy Transmission electron microscopy Dynamic light scattering Biopolymer
Support for aspects of this work from NRCan’s Forest Innovation program is gratefully acknowledged. We thank Drs. Stephanie Beck and Jean Bouchard from FPInnovations, Montreal, for many useful discussions on CNC dispersion and characterization and CelluForce, Inc., Windsor, QC, for providing CNCs to produce the reference material. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.
This study was partially funded by NRCan’s Forest Innovation Program (NRC contributors) and by National Institutes of Health (National Cancer Institute contributors, Contract No. HHSN261200800001E).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Bonevich JE, Haller WK (2010) Measuring the size of nanoparticles using transmission electron microscopy. NIST-NCL Joint Assay Protocol, PCC-7, Washington, DCGoogle Scholar
- Davis CS, Moon RJ, Ireland S, Foster EJ, Johnston LJ, Shatkin JA, Nelson K, Forster AM, Postek MT, Vladar AE, Gilman JW (2015) NIST-TAPPI workshop on measurement needs for cellulose nanomaterials. NIST Special Publication #1192. doi: https://doi.org/10.6028/NIST.SP.1192
- Grulke EA, Yamamoto K, Kumagi K, Hausler I, Osterle W, Ortel E, Hodoroaba V-D, Brown SC, Chan C, Zheng J, Yamamoto K, Yashiki K, Song NW, Kim YH, Stefaniak AB, Schwegler-Berry D, Coleman VA, Jamting AK, Hermann J, Arakawa T, Burchett WW, Lambert JW, Stromberg AJ (2017) Size and shape distributions of primary crystallites in titania aggregates. Adv Powder Technol 28:1647–1659CrossRefGoogle Scholar
- Hamad WY, Hu TQ (2010) Structure-property-yield inter-relationships in nanocrystalline cellulose extraction. Can J Chem Eng 88:392–402Google Scholar
- ISO (19716:2016) Characterization of cellulose nanocrystalsGoogle Scholar
- Rice SB, Chan C, Brown SC, Eschbach P, Han L, Esnor DS, Stefaniak AB, Bonevich J, Vladar AE, Hight Walker AR, Zheng J, Starnes C, Stromberg A, Ye J, Grulke EA (2013) Particle size distributions by transmission electron microscopy: an interlaboratory comparison case study. Metrologia 50:663–678CrossRefGoogle Scholar
- Shatkin JA, Wegner TH, Bilek EM, Cowie J (2014) Market projections of cellulose nanomaterial-enabled products—part 1: applications. TAPPI J 13:9–16Google Scholar