# Steam Explosion-Based Method for the Extraction of Cellulose and Lignin from Rice Straw Waste
## 2 Materials and Methods
### Extraction of Cellulose Fibres from Rice Straw
Post steam-explosion treatment, approximately 70% of the plant material is obtained as a solid residue, primarily consisting of cellulose and lignin, along with some residual hemicelluloses. The solid residue is filtered and washed several times in order to standardise the condition of the biomass before oxidation, ensuring consistency in our experimental results. The supernatant from this step, a lignin-rich solution, is reserved for further extraction, fractionation, and purification, thereby recovering the entire biomass [43; 48; 49]. The effectiveness of the cellulose fibre extraction depends on the swelling of the cellulose, as well as the softening and/or removal of the lignin induced by the steam treatment. **Step 3: Oxidation Treatment:** Following the hydrothermal process, the remaining solid undergoes a subsequent treatment phase involving a 60 mL 30% hydrogen peroxide solution, with a water-to-raw material ratio of 40:1 (mL:g). This phase is conducted in a jacketed glass reactor of 1 L at a steady temperature of 50 \({}^{\circ}\)C, stirring at 400 rpm and with a pH of 11.5 over a period of 3 to 5 h. The application of hydrogen peroxide is a critical step, as peroxides are known to decompose readily into hydroxyl radicals (HO-) through the reaction:  
\[\mathrm{HO-OH}\to 2\mathrm{HO} \tag{2}\]  
These hydroxyl radicals then interact with the hydrogen in the cellulose matrix and fibres, leading to the reaction:  
\[\mathrm{HO}+\mathrm{Cellulose-H}\to\mathrm{Cellulose}+\mathrm{H_{2}O} \tag{3}\]  
As a result of this treatment with hydrogen peroxide, there is a notable decrease in the hydrophilicity of the fibres, as well as an increase in their tensile properties [42; 50; 51]. Together with the previously described steps, a focal point of this study is the examination of the processing time variation during this peroxide treatment, from 3 to 5 h. This investigation aims to identify the optimal duration that maximises both the efficiency and efficacy, thereby contributing to the overall optimisation of the cellulose and lignin extraction process from rice straw. To facilitate the purification of the fibres, post-peroxide treatment, a thorough washing process is employed. The fibres are initially washed with distilled water, followed by a water:ethanol mixture in a 1:1 ratio, and finally, with absolute ethanol. This stepwise purification approach ensures the removal of residual chemicals and impurities, thus enhancing the quality and applicability of the cellulose fibres extracted from the rice straw [52]. **Step 4: Bleaching Process:** This step involves the processing of the extracted cellulose by immersing it in a 3.7 wt% NaClO aqueous solution to eliminate lignin and amorphous cellulose, using a 15:1 (mL:g) solution-to-fibres ratio [53; 54]. The mixture is agitated continuously at 500 rpm for an hour at 70 \({}^{\circ}\)C. After stirring, the product is filtered and washed with water for neutralisation, then lyophilised to a constant weight. Given the overall aim of optimising the extraction process, this stage remains unchanged, as it is crucial for producing a final bleached product that meets industrial application standards. In line with the circular economy principles, the process aims to utilise all constituents of rice straw. The refined method detailed herein builds on the procedures established by [PERSON] et al. (2022) [32] while introducing new process optimisations suitable for the rice straw feedstock. The process efficiency has been evaluated based on the yield and purity of the extracted cellulose and the utility of the byproducts in lignin valorisation.