Sustainable Valorization of Sugarcane Bagasse Through Lignin Extraction, Bioethanol Production, and a Proof of Concept Lignin Application

Sugarcane bagasse (SCB) represents an abundant lignocellulosic residue with significant potential for integrated biorefinery applications. In this study, an alkaline extraction process was optimized for lignin recovery from SCB using a Box–Behnken Design (BBD) to evaluate the effects of extraction temperature (70–110 °C), NaOH concentration (3–9%, w/v), solid-to-liquid ratio (1:10–1:50, g mL−1), and extraction time (30–90 min). Total phenolic content (TPC) and pure lignin content (PLC) were employed as response variables to identify optimal extraction conditions. Under the optimized parameters, a lignin yield of 17.7% and a TPC of 52.7 mg GAE g−1 were achieved. Structural and thermal characterization by Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) confirmed the preservation of characteristic lignin functionalities and adequate thermal stability for downstream applications. To demonstrate its valorization potential, the recovered lignin was successfully incorporated as a partial substitute for petroleum-derived phenol in the formulation of a lignin-based resin, providing a proof of concept for its utilization in sustainable polymeric materials. In parallel, the cellulose-enriched residual solid (RS) obtained after lignin extraction was subjected to fermentation, yielding 10.3 g L−1 ethanol. This integrated strategy enabled the sequential production of lignin-derived materials and bioethanol from a single biomass feedstock, maximizing resource utilization while minimizing waste generation. The findings highlight the feasibility of coupling lignin recovery with biofuel production and support the development of SCB-based biorefineries for the generation of renewable chemicals, bio-based materials, and sustainable energy carriers.