A Green Approach to Rapid Lignin–Carbohydrate Complex Cleavage: Advancing Sustainable Biomass Utilization by Retrieving Structurally Intact Lignin with High Yield

Efficient extraction of structurally intact lignin from biomass is crucial for advancing cellulose accessibility and unlocking the versatile properties of lignin for various sustainable applications. This study introduces an innovative and eco-friendly approach using a natural deep eutectic solvent (NADES) composed of lactic acid and choline chloride in a 5:1 molar ratio, synergistically combined with high-energy microwave technology. The process is optimized for maximum yield and purity; rapid extraction at 450 W in 5 min delivers 95% lignin with >98% purity and preserved aromatic integrity from pineapple leaf biomass. This rapid process efficiently cleaves the lignin–carbohydrate complex (LCC) linkages while preserving crucial β-O-4, β-β, and β-5 linkages within the lignin structure. Comprehensive spectroscopic and analytical techniques, including various NMR methods, are employed to thoroughly characterize the extracted lignin and confirm its structural preservation. Simultaneously, the process leaves behind a holocellulose residue rich in fermentable carbohydrates, serving as an ideal feedstock for bioethanol production. This eco-friendly process represents a significant advancement in green chemistry and sustainable biorefinery practices, enhancing biomass valorization and opening new avenues for lignin's multifunctional applications across diverse sectors, from materials science to renewable energy.