Agglomeration of cellulose nanocrystals: the effect of secondary sulfates and their use in product separation
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ORIGINAL RESEARCH
Agglomeration of cellulose nanocrystals: the effect of secondary sulfates and their use in product separation Christoph Metzger Heiko Briesen
. David Auber . Stephan Da¨hnhardt-Pfeiffer .
Received: 19 June 2020 / Accepted: 19 September 2020 Ó The Author(s) 2020
Abstract This study was aimed at the development of a better understanding of the agglomeration behavior of sulfated cellulose nanocrystals (CNCs) in the presence of sulfates with monovalent (NH4?, K?, Na?) and divalent (Ca2?) cations, and to demonstrate their potential in simple and efficient product separation. Protonated CNCs were counterion-exchanged and their ionic strength was increased by adding sulfates of the respective cation to trigger agglomeration. The critical concentrations of agglomeration (CAC) and peptization (CPC) were determined. We found that the agglomeration behavior of CNCs could be attributed to matching affinities between the cations and the sulfate half-ester groups on the CNC surfaces. Based on these findings, a facile and efficient downstream process was designed to separate CNCs from neutralized reactant solutions using CAC and CPC. This method provides
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10570-020-03476-0) contains supplementary material, which is available to authorized users. C. Metzger (&) D. Auber H. Briesen Chair of Process Systems Engineering, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Munich, Germany e-mail: [email protected] S. Da¨hnhardt-Pfeiffer Microscopy Services Da¨hnhardt GmbH, Plambeckskamp 2, 24220 Flintbek, Germany
colloidally stable CNCs at high yield provided by centrifugation. When salt concentrations in the product are maintained below the CAC, as prepared CNCs from neutralized reactant solutions might be used in hydrogels and emulsions. Keywords Cellulose nanocrystals Agglomeration Peptization Colloidal behavior UV–Vis Separation efficiency
Introduction Cellulose nanocrystals (CNCs) are nanorods with widths ranging from 3 to 50 nm and aspect ratios from 5 to 50 (ISO 2017b). They have received an increasing amount of attention from academia and industry alike due to their straightforward production and their remarkable physical and chemical properties, which make them high-performance building blocks for a wide range of potential commercial applications (Cowie et al. 2014; Thomas et al. 2018; Dufresne 2019). CNCs are commonly produced by sulfuric acid-catalyzed hydrolysis of purified cellulosic feedstock extracted from botanical sources, tunicates, or bacteria (Habibi et al. 2010; Sacui et al. 2014), although numerous extraction methods exist (Trache et al. 2017). Hydrolytic cleavage of glycosidic linkages and further breakdown of cellulose to glucose and
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oligosaccharides, as well as conversion to 5-(hydroxymethyl)furfural preferably occurs in the amorphous domains of cellulose (Sun et al. 2016), leaving CNCs
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