Extraction of cellulose nanocrystals using a recyclable deep eutectic solvent

Cellulose nanocrystals (CNCs) have been widely used as renewable materials and tough nano-composites due to its excellent properties. Currently, the preparation methods of CNCs require substantial energy and time consumption and the use of toxic chemicals. Herein, cotton and other biomass feedstocks were treated with deep eutectic solvents (DESs) and subsequent high-pressure homogenization (HPH), which was a simple preparation procedure for CNCs. The morphological, spectroscopic, and stability properties of the as-prepared rod-shaped CNCs were characterized using zeta potential, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, fourier transform infrared spectroscopy and thermogravimetric techniques. CNCs with a diameter range of 50-100 nm and a length range of 500-800 nm were successfully assembled. The resulting CNC suspension was stable even after one month of storage. The solvent could be recycled successfully and reused for at least three additional pretreatment cycles while maintaining its pretreatment capability. The use of a DES as both the catalyst and solvent introduces a green chemical process that does not produce any hazardous waste and is an economical process because of the high recyclability (> 85%). The molecular structure changes of cellulose after HPH and DES treatment were also discussed. This is the first report on the recycling and reuse of a DES after preparing CNCs. Graphic abstract