Cellulose nanofibrils (CNFs) are typically liberated under mechanical nanofibrillation. Unfortunately, due to the inter- and intramolecular hydrogen bonding evident in cellulose, mechanical nanofibrillation requires intense energy. Thus, various pretreatments have been recently adopted to reduce energy consumption such as enzymes, base, and chemical modification. Such pretreatment allows for a modification of the large number of hydroxyl groups of cellulose with carboxylates (e. g., carboxymethyls) and aldehydes.
  Sulfation is a process that introduces sulfate groups to the surface of cellulose. The sulfation reaction in nanocellulose preparation is usually was carried out to prepare cellulose nanocrystal (CNC) by sulfuric acid hydrolysis. However, it is not suitable to modify CNF due to the high acidity of sulfuric acid, which is easy to hydrolyze the amorphous region in CNF. Furthermore, sulfated cellulose was reported to prepare CNF, but it was not suitable for further mechanical treatment to prepare sulfated CNF since the fibril structure of the prepared sulfated cellulose was destroyed or aggregated. Post-sulfonation were also used to prepare sulfated CNF, as described by Luo et al, CNF were successfully post-sulfonated with a dimethylformamide and chlorosulfonic acid with a high surface charge while retaining fibrous morphology. But this method was complex and chlorosulfonic acid used was hazardous.
  Deep eutectic solvent (DES) is the new generation of green solvent composed of a hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA). It has the advantages of environmental compliance, low cost, biodegradability, non-toxicity and renewability. Recently, DES has been applied for organic synthesis, catalysis, material chemistry, and electrochemistry. Lately, studies on the use of DES in cellulose functionalization (e.g., cationic functionalization, phosphine functionalization, carbamate functionalization) and preparation of various types of nanocellulose have emerged.
  In this work, DES synthesized by sulfamic acid (HBA) and glycerol (HBD), and a sulfamic acid-urea-choline chloride (ternary deep eutectic solvent) system were used as the pretreatment medium to synthesize sulfated CNF using a supermasscolloider. The sulfated fiber was analyzed through fiber quality analysis, elemental analysis, degree of polymerization (DP) and Fourier transform infrared spectrometry (FTIR). The CNF was analyzed by water retention (WRV), atomic force microscopy (AFM), and X-ray diffraction (XRD). The mechanical energy consumption during CNF production was also analyzed.
 

Deep eutectic solvent (DES),Cellulose nanofibril (CNF),Sulfation