## 3 Results and Discussion
### Cellulose Dissolution  
The process of 5 wt % cellulose dissolution in the NA ILs at 50 \({}^{\circ}\)C was observed using the polarizing microscope, as shown in Figure 1. The dissolution phenomena corresponding to QA and TA ILs were similar to those corresponding to NA, and the cellulose dissolution rate of these QA RTILs were in the order of NA \(>\) TA \(>\) QA. It was also found that the three QA RTILs could break cellulose intramolecular and intermolecular hydrogen bonds in a short time. The acetate anions in the QA RTILs exhibited strong hydrogen bonding capacity to destroy the cellulose structure. The conjunction of the spatial heterogeneity in QA RTILs with an amphiphilic cation triggered the aggregation of alkyl tails. The hydrophobic tail aggregation implies a trend to make other parts more hydrophilic and polar. Hence, an appropriate increase in alkoxy chains leads QA RTILs to be more powerful cellulose solvents, through increasing the spatial heterogeneity and the activity of acetate anions. [18; 19] On the same molar basis, although QA has the longest alkyl chain and twice the acetate anion content of TA and NA, its dissolution ability for cellulose is the weakest among these QA RTILs. The amphiphilic properties of QA RTILs are decreased with the increase in alkyl number, resulting in an increase of the viscosity. NA with the polar cation and lower viscosity exhibits the best cellulose dissolution ability. The ILs with lower viscosity exhibit better ionic mobility, which plays an important role in the cellulose dissolution reaction. Figure 1 indicates that the cellulose main structure was destroyed in NA within 5 min, and many fine light spots were produced. The image became dark after 20 min of reaction due to the complete dissolution of cellulose. In the initial 5 min, the dissolution occurred very rapidly. Then, the dissolution rate decreased due to the crystalline structure in the residual cellulose fibrils (fine light spots labeled in Figure 1c) and the increase in ILs viscosity during the cellulose dissolution. The results show the good cellulose dissolution ability of NA, and the swelling of cellulose in NA was not observed, unlike in the case of the NMMO and AMIMCI systems. Cellulose dissolved well in the AMIMCI system at 60 \({}^{\circ}\)C, but cellulose swelling in AMIMCI was observed only at room temperature [7]. Moreover, we used water, dilute acetic acid, and dilute nitric acid in the dissolution test at 80 \({}^{\circ}\)C for 2 h, and only a two-phase liquid was formed due to the swelling of cellulose, and some cellulose was precipitated. These solutions are not easy to use as coating solutions for the preparation of regenerated cellulose films. Therefore, these solvents are not suitable as regenerating fiber film reagents.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**ILs** & **Cation Structure** & **Molecular Weight** & **Melting Temperature** & \(\eta\)**a** (cp) & **E\({}_{\text{flow}}\)**b** (kcal/mol)** & **T\({}_{\text{d}}\)**c** \\ \hline QA & 461 & \(<\)–70 \({}^{\circ}\)C & 886 & 10.7 & 180 \({}^{\circ}\)C \\ TA & 414 & \(<\)–70 \({}^{\circ}\)C & 443 & 9.2 & 173 \({}^{\circ}\)C \\ NA & 245 & \(<\)–70 \({}^{\circ}\)C & 59 & 8.1 & 180 \({}^{\circ}\)C \\ \hline \end{tabular}  
* \({}^{\text{a: Room temperature viscosity;}}\) b: Viscous flow activation energy; c: Decomposition temperature.  
\end{table}
Table 1: Physical properties of quaternary ammonium-based room-temperature ionic liquids (QA RTILs).