Properties of Cellulose Nanocrystals Extracted Using Deep Eutectic Solvents

Cellulose nanocrystals (CNCs) are biosourced colloidal building blocks that have attracted significant scientific attention due to their unique properties, such as high mechanical strength, biodegradability, nontoxicity, and potential for sustainable material development. Acidic hydrolysis utilizing strong acids, mainly sulfuric acid, remains the predominant method for CNC production on both laboratory and commercial scales. However, this approach involves challenges associated with the use of corrosive reagents, acid neutralization, and extensive purification. Deep eutectic solvents (DESs) have been proposed as alternative processing media for CNC extraction, with potential advantages including reduced reliance on concentrated mineral acids and opportunities for solvent recovery and recycling. Here, we report a detailed characterization of DES-extracted CNCs and their characteristics and properties contrasted with those of commercial acid-extracted CNCs. The DES-CNCs were dispersible but with lower ζ-potential and typically longer lengths, forming colloidal gels down to low concentrations that prevent the formation of liquid crystalline phases at higher concentrations, while ultrasound application and increased ionic strength were also found to promote aggregation. The mechanical response of these eutectic-extracted CNCs is followed by linear and nonlinear rheometry at different concentrations and is compared to that of commercial sulfuric acid-extracted CNCs.