# Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste
## 3 Results and Discussion
### Characterisation of Cellulose Fibres
This technique surpasses traditional wet chemical methods in accuracy [67] and is particularly adept for the high-throughput examination of polymers such as cellulose and lignin. The data in Figure 8 elucidate the thermal degradation patterns of both biomass waste and the fibres derived from its processing in the research, as analysed using a TGA. The differential thermal decomposition behaviours observed in cellulose, hemicellulose, and lignin can be attributed to their unique molecular structures and chemical properties. Hemicellulose, comprised of a variety of sugars such as xylose, mannose, glucose, and galactose, presents a disordered, non-crystalline, and branched architecture [70]. This structure is responsible for its earlier decomposition into volatile substances (including CO, CO\({}_{2}\), and various hydrocarbons) at lower temperatures, typically in the 200-300 \({}^{\circ}\)C range [71]. Contrasting with hemicellulose, cellulose--a glucose-based polymer linked by \(\beta\)-1,4 glycosidic bonds--exhibits an enhanced strength and thermal resistance, decomposing mainly between 300-370 \({}^{\circ}\)C [71]. Lignin, out of the three, shows the most substantial thermal stability, a characteristic stemming from its complex network of aromatic rings and diverse branching patterns, resulting in a wider decomposition temperature spectrum (200-500 \({}^{\circ}\)C) [32]. The weight loss observed below 110 \({}^{\circ}\)C is primarily due to the release of moisture associated with the hydroxyl and carboxyl groups in the fibres [72]. In the context of optimising the biomass pretreatment, Figure 8b displays the differential thermal analysis (DTA) curves derived from the TGA data, which have facilitated the determination of specific degradation ranges for the principal lignocellulosic components: hemicellulose, cellulose, and lignin. Based on these data, the TGA weight loss curves shown in Figure 8a were standardised, enabling the extraction of precise compositional percentages across varying durations of steam explosion treatment, both with and without the application of ScCO\({}_{2}\)[57]. The yields for each condition have also been provided. Table 3 illustrates the compositional breakdown and yields of the biomass subjected to different treatment durations. When examining the influence of the reaction time on the results shown in Table 3, notable trends become apparent. In both cases, with and without ScCO\({}_{2}\) as the reaction time increases, the yield consistently decreases. However, the behaviour of the cellulose  
Figure 8: (**a**) TGA and (**b**) DTA curves corresponding to rice waste and the resulting fibres. content differs significantly. In the ScCO\({}_{2}\)-involved reactions, there is a clear trend of maintaining the cellulose percentages regardless of the reaction time. Conversely, in the absence of ScCO\({}_{2}\), the cellulose percentage decreases with longer reaction times. When comparing the conditions, the data indicate that a 33 min steam explosion without ScCO\({}_{2}\) yields the highest percentage of cellulose (77.36% \(\pm\) 0.94%) and the lowest percentage of lignin (8.33% \(\pm\) 0.10%), with a notable yield of 23.00% \(\pm\) 0.15%. This suggests an efficient delignification and the preservation of cellulose content, which is crucial for subsequent conversion processes. In contrast, longer durations and the introduction of ScCO\({}_{2}\) do not significantly enhance the cellulose content or yield. Specifically, ScCO\({}_{2}\) treatments appear to retain higher percentages of hemicellulose and lignin, with a subsequent decrease in the cellulose percentage. Likewise, as mentioned before, the yield consistently declines with extended treatment times, particularly noticeable at the 4 h mark with both ScCO\({}_{2}\) and non-ScCO\({}_{2}\) processes. Therefore, the 33 min steam explosion treatment stands out as the most favourable, achieving a balance between cellulose preservation, lignin removal, and overall yield, thereby positioning as a key parameter for efficient biomass conversion.