# Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste
## 3 Results and Discussion
### Characterisation of Cellulose Fibres  
An FTIR spectroscopic analysis was conducted to examine the chemical properties of the cellulose extracted from rice straw after a four-stage process, including steam explosion with and without ScCO\({}_{2}\) addition. The FTIR spectra of both the extracted cellulose fibres and the rice straw waste are displayed below. The most characteristic peaks associated with typical functional groups found in biomass confirm the presence of cellulose in the samples, as outlined in Table 2.  
The FTIR spectrum of the untreated rice straw serves as a baseline, presenting an -OH stretching band at 3400 cm\({}^{-1}\), attributed to the hydroxyl groups in cellulose, hemicellulose, and lignin [7]. Water absorption is evidenced by a peak at 1640 cm\({}^{-1}\)[32]. Aliphatic C-H stretching vibrations are observed around 2900 cm\({}^{-1}\)[8]. The peaks at 1429 cm\({}^{-1}\) and 1375 cm\({}^{-1}\) correspond to the symmetric deformation of -CH\({}_{2}\) and -CH\({}_{3}\), respectively [27; 68], while bending vibrations of \(\beta\)-glycosidic C-H bonds are identified at 897 cm\({}^{-1}\)[8; 27]. This spectrum serves as a comparison to identify the effects of the treatments applied to rice straw. Figure 6 shows the FTIR spectra for the rice straw raw material and the cellulose fibres extracted after different steam explosion treatments using ScCO\({}_{2}\). The samples treated with CO\({}_{2}\) exhibit significant changes in their vibration bands. At 33 min of treatment, there is a notable decrease in the ratio between the -OH stretching band at 3400 cm\({}^{-1}\) and the aliphatic C-H stretching vibration at 2900 cm\({}^{-1}\), compared to the rice straw raw material spectrum, suggesting potential hydrogen bond breaking and initial \begin{table}
\begin{tabular}{c c c} \hline
**Wavenumber (cm\({}^{-1}\))** & **Assignment** & **References** \\ \hline
3400 & -OH group stretching & [7] \\
2900 & C–H stretching vibration & [8] \\
1640 & Water absorption & [27; 32] \\
1429 & Symmetric deformation of -CH\({}_{2}\) & [27] \\
1375 & Symmetric deformation of -CH\({}_{3}\) & [68] \\
897 & Bending vibrations of \(\beta\)-glycosidic C–H bonds & [27; 32] \\
1054–1155 & Stretching vibrations of C–O and C–O–C & [29; 69] \\ \hline \end{tabular}
\end{table} 
Table 2: Infrared band assignments for cellulose, hemicellulose, and lignin. Figure 5: Comparison of the results obtained for the steam explosion stage at different times and with or not without ScCO\({}_{2}\). depolymerisation [7; 8]. As the treatment time increases, the ratio between the C-H stretching vibration at 2900 cm\({}^{-1}\) and the C-O stretching bands at 1054 cm\({}^{-1}\) and C-O-C at 1155 cm\({}^{-1}\) progressively increases, indicating cellulose and hemicellulose degradation [29; 32]. Conversely, Figure 7 shows the samples treated without CO\({}_{2}\), compared to the raw material, which show a smaller decrease in the ratio between the -OH and C-H stretching bands, suggesting a more effective preservation of the cellulose structure. At 33 min, the ratio between the -CH stretching vibration at 2900 cm\({}^{-1}\) and the C-O stretching band at 1054 cm\({}^{-1}\) experiences a slight decrease, indicating minor cellulose structure alterations, but at 4 h, a recovery in its intensity is observed, which might reflect a stabilisation of the cellulose structure after undergoing oxidation and bleaching treatments. Figure 6: FTIR spectra of rice straw waste and the cellulose fibres extracted after different durations of steam explosion treatment using ScCO\({}_{2}\). Figure 7: FTIR spectra of rice straw waste and the cellulose fibres extracted after different durations of steam explosion treatment. Likewise, the thermogravimetric analysis (TGA) demonstrated a remarkable efficacy in identifying and quantifying the components of plant-based materials, specifically \(\beta\)-cellulose, lignin, and hemicellulose.