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 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.
Highlights
Cellulose nanocrystals (CNCs) are nanorods with widths ranging from 3 to 50 nm and aspect ratios from 5 to 50 (ISO 2017b)
The agglomeration behavior of cellulose nanocrystals extracted from ashless cotton cellulose was studied in the presence of four secondary sulfates with monoand divalent cations from Groups 1 and 2 of the periodic table
An increase of ionic strength led to progressively greater agglomeration between the critical concentrations of agglomeration (CAC) and the critical peptization concentration (CPC)
Summary
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), numerous extraction methods exist (Trache et al 2017). CNCs produced by sulfuric acid-catalyzed hydrolysis usually contain between 240 and 330 mmol of sulfate per kg of CNCs (Dong et al 1996; Araki et al 1999)
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