## 3 Results
### DES Treatment
#### 3.2.2 FTIR and XRD Analysis of CR  
It is concluded from Section 3.2.1 that temperature and additional water supplementation are crucial factors during DES treatment; FTIR and XRD analyses of CR prepared under different treatment temperatures and water addition were therefore thoroughly investigated, as shown in Figure 5a-d. The signal at 1737 cm\({}^{-1}\) in Figure 5a is strengthened significantly and enhanced with the increase in treatment temperature. In general, the signal at 1737 cm\({}^{-1}\) is deemed the carbonyl stretching of acetyl or carboxylic groups [41]. It is known that pseudo-lignin containing carbonyl, carboxylic, aliphatic, and aromatic structures can be derived from the degradation of cellulose, especially in the company of high temperatures, acids, and oxygen [51; 52; 53]. Thus, \(\alpha\)-cellulose and long-staple cotton were selected to be treated with ChCl-LA (Figure 5e), and the presence of an obvious and strong signal at 1737 cm\({}^{-1}\) in the FT-IR spectra of (ChCl-LA)-treated \(\alpha\)-cellulose and (ChCl-LA)-treated cotton probably verify the transformation of cellulose to pseudo-lignin [51]. The other possible reason for the newly generated signal at 1737 cm\({}^{-1}\) is the esterification of LA with hydroxyl groups of cellulose [54]. In Figure 5b, the signal at 1514 cm\({}^{-1}\) becomes stronger as the water content increases from 0% to 60%, reflecting that water addition in ChCl-LA exerts a negative effect on delignification, which further demonstrates the conclusion drawn in Section 3.2.1 that anhydrous ChCl-LA is more beneficial to delignification.  
Seen from Figure 5c, the _CrI_ of HTB was 60.3%, and an initial increase in _CrI_ of CR may suggest effective removal of the amorphous portion (mainly lignin) and an enhanced exposure of crystalline cellulose [22], while a gradual decrease in _CrI_ could be seen when the temperature was increased from 110 \({}^{\circ}\)C to 160 \({}^{\circ}\)C, probably indicating that the ordered polymer chain of bamboo cellulose was disrupted. However, it is observed in Figure 5d that the _CrI_ of CR increased first and then nearly reached a plateau when the water content in ChCl-LA was higher than 10%. It is suggested that excessive water addition to ChCl-LA leads to a limited disruption to lignocellulosic structure. In addition, XRD spectra of \(\alpha\)-cellulose and long-staple cotton before and after ChCl-LA treatment are exhibited in  
Figure 4: Lignin removal and cellulose retention under DES treatment conditions of: (**I**) molar ratio of ChCl to LA of 1:3-1:15, 120 \({}^{\circ}\)C, 3 h, 1:25 g/mL without water addition; (**II**) molar ratio of ChCl to LA of 1:3, 90–160 \({}^{\circ}\)C, 3 h, 1:25 g/mL without water addition; (**III**) molar ratio of ChCl to LA of 1:3, 140 \({}^{\circ}\)C, 1–5 h, 1:25 g/mL without water addition; (**IV**) molar ratio of ChCl to LA of 1:3, 140 \({}^{\circ}\)C, 2 h, 1:10–1:30 g/mL without water addition; (**V**) molar ratio of ChCl to LA of 1:3, 140 \({}^{\circ}\)C, 2 h, 1:10 g/mL, and water addition of 0–60% (%).  
Figure 5f, and the results verify that ChCl-LA treatment can increase the \(Crl\) of cellulose or cellulose-rich biomass.