## 4 Technologies for Nanocellulose Production
### Ionic Liquid Pretreatment  
Ionic liquid (IL) pretreatment of LB is a greener pretreatment strategy, which has gained a lot of attention over the last decade. ILs are salts of organic cation and inorganic/organic anions that are liquid at room temperature (<100 \({}^{\circ}\)C). They possess various green properties such as a low vapor pressure, non-flammability, non-corrosive, high thermal and chemical stability [75]. The mechanism of IL action is based on the dissolution of cellulose in biomass by IL [76]. The significant inter- and intramolecular hydrogen bonding in the cellulose is broken down as a result of the hydrogen bond that forms between the anionic component of the IL and the hydroxyl group proton of the cellulose, which leads to the cellulose dissolution and disruption of the complex network of LB [26; 75; 77]. ILs are also known as \"designer solvents\", as they can be designed with tunable properties by altering the branching, cation or anion substituent and length of alkyl chain of the cation according to the biomass to be pretreated [19; 77]. ILs can be used alone or in combination with other physical/chemical pretreatment approaches for biomass pretreatment. Pretreatment of herb residues using 1-butyl-3-methylimidazol chloride ([Bmim]Cl), assisted by aromatic acid (p-toluenesulfonic acid, TsOH), resulted in an increased cellulose recovery yield (96.4%) and lignin removal rate (79.9%) under optimal conditions of 79% IL, 1.0% TsOH and 20% H\({}_{2}\)O at 130 \({}^{\circ}\)C for 2 h [78]. Bamboo biomass was subjected to ultrasound-assisted 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) pretreatment, which resulted in 69.3% and 14.9% yield of cellulose-rich and lignin-rich materials, respectively [79]. ILs have been also used for the preparation of NC from extracted cellulose. A study reported the use of 1-butyl-3-methylimidazolium chloride (BmimCl) for the preparation of cellulose nano-fibrils from sugarcane bagasse. The diameter of the prepared cellulose nano-fibrils was between 4 and 35 nm [80].  
Deep Eutectic Solvent Pretreatment  
Deep eutectic solvents (DES) are the viable replacements of ILs, as they overcome the limitations of ILs such as high cost, toxicity and non-biodegradability, among others. DESs are made by mixing a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) in particular molar ratios in solid-phase, to form liquid phase eutectic mixtures at a moderate temperature (60-80 \({}^{\circ}\)C) and ambient pressure conditions [2; 81]. The hydrogen bond (H-bond) between HBA and HBD promotes charge delocalization, resulting in a DES with a melting point lower than that of its individual components. They may also be regarded as eutectic mixtures of Lewis or Bronsted acids and bases that form a solution. A stronger H-bond causes a greater melting point decline [82]. DES pretreatment has been executed on various LBs for cellulose extraction and lignin removal. Pretreatment of corncob with DES choline chloride/ethanolamine led to the delignification of 83.12% [83]. DES choline chloride/formic acid was used for the pretreatment of corn stover, which resulted in the lignin removal of 23.8% with 47.9 \(\pm\) 0.3% cellulose [84]. DES pretreatment has also been used for cellulose nanofibril preparation from ramie fibers. Pretreatment with DES choline chloride-oxalic acid dihydrate for 4 h at 100 \({}^{\circ}\)C resulted in the production of cellulose nanofibrils with 90.31% pure glucan, and a width of 14.29 nm and crystallinity at 79.17% [85].