# Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste
## 4 Conclusions  
This study explores the extraction of cellulose and lignin from rice straw through a four-stage process, focusing on varying and optimising each stage to determine the most efficient conditions. Upon completion of the experimentation, it was concluded that the ideal approach excludes the alkaline pretreatment stage and involves three hours of oxidation and one hour of bleaching. The study also evaluates the effect of ScCO\({}_{2}\) in the steam explosion stage over different durations (from 33 min to 4 h) based on different characterisation techniques.  
The consolidated findings from various analyses indicate significant chemical, thermal, and structural changes in the cellulose extracted from rice straw. The FTIR and SEM analyses revealed that non-ScCO\({}_{2}\) treatments effectively retained the cellulose structure while upholding a superior fibrous structure in the samples. This observation aligns with the TGA results, which identified a 33 min steam explosion treatment without ScCO\({}_{2}\) as optimal for maintaining the cellulose integrity and for effective lignin removal. XRD patterns confirmed the presence of crystalline cellulose \(\upbeta\), with non-ScCO\({}_{2}\) treated samples exhibiting a more effective preservation of the crystalline structure of cellulose. These results demonstrate the significant influence of the treatment conditions on the properties of rice straw-derived cellulose.  
Furthermore, regarding the extraction of lignin from the supernatant of the steam explosion stage, the four processes considered most optimal for cellulose extraction were selected and analysed using FTIR and TGA. The TGA results showed that the 33 min steam explosion condition without ScCO\({}_{2}\) yields a higher lignin content compared to other conditions, and the absence of ScCO\({}_{2}\) improved the selectivity of lignin extraction. FTIR analysis also revealed that the 33 min condition better preserves the aromatic ring structure of lignin compared to longer treatments or those with ScCO\({}_{2}\).  
To conclude, the study highlights the effectiveness of specific treatment conditions in preserving the cellulose integrity, which is crucial for its application in the production of high-quality nanocellulosic materials, while laying the groundwork for future efforts in lignin purification, emphasising the effectiveness of the optimised steam explosion conditions in lignin extraction from rice straw.  
Conceptualisation and investigation, V.M.S.-M. and H.P.-A.; methodology, V.M.S.-M.; validation and formal analysis, V.M.S.-M. and H.P.-A.; writing--original draft preparation, V.M.S.-M.; writing--review and editing, V.M.S.-M., H.P.-A. and M.P.C.-B.; supervision, F.A.-A. and E.O.-C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Ministry of Science and Innovation (MCIN) and the State Research Agency (AEI) through the grant number TED2021-129932B-C22, BioTech-RICE.  
Not applicable.  
Data Availability Statement:Data is contained within the article.  
The authors declare no conflicts of interest.