This study investigates the structural effects of dilute acid and alkali treatments on cotton fibers, aiming to understand the influence of chemical pretreatment on cellulose morphology. Cotton samples were exposed to 1% sulfuric acid and 1% sodium hydroxide at 90 °C, and the resulting changes were evaluated using scanning electron microscopy and nonlinear optical imaging techniques. The results indicate that sulfuric acid causes significant fiber degradation, leading to fragmentation and reduced fiber thickness. In contrast, sodium hydroxide treatment results in a roughened, flaky surface while preserving the overall structural integrity, with fibers appearing fluffier and more accessible to enzymatic processes. Untreated cotton fibers maintained a smooth and uniform surface, confirming the chemical specificity of the observed changes. These findings are crucial for optimizing biomass pretreatment methods, demonstrating that dilute chemical treatments primarily affect macrostructural features without significantly disrupting the cellulose microfibrils. The study provides valuable insights for the development of efficient biorefining processes and sustainable bio-based materials, highlighting the importance of selecting appropriate chemical conditions to enhance enzymatic hydrolysis and biomass conversion while maintaining the core structure of cellulose. This research contributes to advancing the understanding of cellulose’s structural resilience under mild chemical pretreatment conditions.

Oil and natural gas continue to dominate global energy consumption, though a supply gap of 2 million barrels per day (b/d) was reported in the fourth quarter of 2023. Despite a projected increase in global oil supply by 1.2 million b/d in 2023, reaching 101.1 million b/d compared to 2022, reliance on fossil fuels poses challenges for energy security and sustainability. For China, transitioning to clean and renewable energy sources is essential. Biofuel ethanol, with its high octane rating and anti-knock properties, is a promising alternative. This bioenergy sector is expanding globally, with cellulosic ethanol production emerging as a key objective. However, the high production cost of cellulosic ethanol presents a significant challenge to its large-scale adoption. To overcome this barrier, various techniques are being explored to reduce production costs. Among them, advanced characterization methods are used to monitor changes in cellulose, lignin, and hemicellulose during ethanol production in situ, quickly and without surface labeling. These methods provide insights into the factors driving high production costs, enabling targeted improvements. This review focuses on the potential of these characterization techniques to optimize ethanol production processes and improve efficiency. The findings may offer a strategic direction for scaling up cellulosic ethanol production and contribute to the sustainability of energy resources by reducing dependency on fossil fuels.