## 3 Results and Discussions
### Alkaline Fractionation for High Glucan Content and XMG Yield  
In our previous study on the NaOH fractionation of RH, the highest xmg extraction yield was obtained at a reaction temperature of 148.1 \({}^{\circ}\)C, reaction time of 27.0, and NaOH concentration of 5.9%, whereas the maximum de-ashing yield was achieved at a reaction temperature of 142.8 \({}^{\circ}\)C, reaction time of 60.6 min, and NaOH concentration of 4.9%, which were predicted by statistical analysis and simulation. For the delignification of RH, alkaline fractionation was performed with aqueous NaOH, which breaks the ester bond between lignin and hemicellulose, thereby increasing the porosity in the internal structure of RH. In addition, NaOH reacts with silica in RH to form sodium silicate, so the silica components are also dissolved and released. That is, it is possible to obtain the desired outcomes of delignification and de-ashing [36]. The alkaline fractionation results, which are represented by the percentage changes in the glucan, XMG, ash, and lignin contents of Fr. RH, are presented in Figure 3. These changes represent the relative changes in compositional content due to solubilization under different conditions of RH fractionation. Figure 3 shows the profiles of changes in glucan, XMG, lignin, and ash content of Fr. RH according to the changes in the reaction temperature and time at a NaOH concentration of 6.0 wt.%. The efficacies of fractionation processes are defined as the compositional change in delignified and de-ashed RH over the complete composition of raw RH. The lignin contents in the residual RH after NaOH fractionation ranged from 28.9% (130 \({}^{\circ}\)C and 20 min) to 13.5% (170 \({}^{\circ}\)C and 60 min), and the XMG content \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Elements**} & \multicolumn{2}{c}{**Inner Surface**} & \multicolumn{2}{c}{**Outer Surface**} \\ \cline{2-5}  & **Weight \%** & **Atomic \%** & **Weight \%** & **Atomic \%** \\ \hline C & 45.99 & 53.89 & 23.91 & 33.64 \\ N & 4.53 & 4.55 & - & - \\ O & 44.61 & 39.24 & 45.58 & 48.14 \\ Si & 2.99 & 1.50 & 29.30 & 17.63 \\ S & 1.88 & 0.83 & 0.72 & 0.38 \\ Ca & - & - & 0.50 & 0.21 \\ Total & 100 & & 100 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Elemental weights and atomic percentages of the inner and outer surfaces from EDX spectra of rice husk. Figure 2: SEM images of inner and outer surfaces of rice husk. (**a**) Inner surface (100\(\times\) magnification), (**b**) inner surface (500\(\times\)), (**c**) outer surface (100\(\times\)), (**d**) outer surface (500\(\times\)). of the Fr. RH ranged from 4.3% (170 \({}^{\circ}\)C and 60 min) to 22.7% (130 \({}^{\circ}\)C and 20 min). As shown in Figure 3a, the glucan content increased to some extent and remained constant at 150 \({}^{\circ}\)C, while the other components gradually decreased as time increased, which confirms that cellulose is highly resistant to solubilization during the alkaline delignification process. On the other hand, the glucan content in the higher-temperature region in Figure 3b,c peaked at 77.4% (at 150 \({}^{\circ}\)C) and 65.5% (at 170 \({}^{\circ}\)C) after a fractionation time of 40 min, and the yield decreased as fractionation time increased. This indicates that some glucans were solubilized due to harsher reaction conditions and longer reaction times. It was also confirmed that almost no ash remained in the residual RH and Fr. RH under harsher fractionation conditions. However, the alkaline fractionation performance could not be clearly evaluated with the apparent compositional changes in the Fr. RH, although different fractionation processes at various operational conditions were inferred to have resulted in different amounts of residual solids. In addition, Figure 3 also shows the compositional changes in Fr.