This paper, written by researchers from Xi'an Jiaotong University and others, discusses Efficient Cleavage of Strong Hydrogen Bonds in Cotton by Deep Eutectic Solvents and Facile Fabrication of Cellulose Nanocrystals in High Yields. The paper is published in an important journal < ACS Sustainable Chemistry & Engineering>. IF：6.140.

In recent years, the research work of microwave chemical instrument used in the synthesis of materials has become a hot direction of scientific research, which has been paid great attention to by many scholars!

The content of cellulose in biomass is important for producing nanocellulose in high yields. Cotton fibers containing ultrahigh purity (∼95%) cellulose are ideal feedstock for nanocellulose production. However, the presence of strong hydrogen bonding between the cellulose chains limits the use of cotton fibers for the production of nanocellulose in a facile and mild process. Here, efficient cleavage of the strong hydrogen bonds in cotton and ultrafast fabrication of cellulose nanocrystals (CNCs) with a high yield of 74.2% were first realized through a 3 min microwave-assisted deep eutectic solvent pretreatment and a subsequent high-intensity ultrasonication process. The obtained CNCs had diameters of 3− 25 nm, and lengths ranged between 100 and 350 nm. The CNCs also displayed a relative crystallinity of 82%, and the thermal degradation temperature started from 320 °C. The study provides a green and efficient method for the mass production of cotton CNCs, and is expected to contribute to improving the refinery utilization of cotton feedstock.

In summary, this study demonstrated a facile, fast, and green method to produce qualified CNCs with high yields from cotton. The choline chloride/oxalic acid dihydrate MwDES pretreatment was efficient for the cleavage of the strong hydrogen bonds in cotton and swelling of the undissolved fragments. The combination of MwDES pretreatment and high-intensity ultrasonication had a synergetic effect on disintegrating the fiber fragments into CNCs. The MwDES pretreatment under 800 W at 80 °C for 3 min and ultrasonication at 1200 W for 30 min were determined to be optimal, and the yield of CNCs was 74.2%. The CNCs showed uniform morphology with diameters in the range 3−25 nm and lengths within 100−350 nm. They also showed high crystallinity (82%) and high thermal stability (>320 °C). Therefore, the presented method facilitates the green and fast processing of cotton while not affecting the yield and properties of the CNCs.

CFs (0.25 g) were mixed with 10 g of DES in a Teflon-lined polyetheretherketone tank. The tank was heated to between 70 and 100 °C using an XH-800C microwave accelerated reaction system (Xianghu Technology Co., Ltd., Beijing, China) under 800 W microwave radiation (Figure S1 in the Supporting Information). The program was set with the conditions listed in Table 1. After MwDES pretreatment, the undissolved matter was separated and washed with acetone and water. For convenience, the MwDES-pretreated CFs were named MwDES-70, MwDES-80, MwDES-90, and MwDES-100, where the suffix indicates the pretreatment temperature. The yield of the CFs was calculated as the weight percentage of the oven-dried CFs to the oven-dried cotton feedstock.