Surfactants as process intensifiers in lignocellulosic sugar-platform biorefineries: Mechanistic insights and...

The recalcitrance of lignocellulosic biomass, stemming from its complex cellulose-hemicellulose-lignin matrix, remains the primary techno-economic bottleneck in sugar-platform biorefineries. Surfactants have emerged as versatile process-intensifying agents capable of overcoming these interfacial and chemical barriers. While previous reviews have largely focused on macroscopic yield improvements, a critical synthesis elucidating the molecular-level surfactant-biomass-enzyme interplay is lacking. This review provides a comprehensive analysis of surfactant-mediated mechanisms across both pretreatment and enzymatic hydrolysis. Uniquely, we highlight the role of surfactants beyond physical dominance, detailing their capacity to induce in-situ chemical modifications of lignin during pretreatment. Mechanisms such as surfactant grafting via α-etherification, phenolic hydroxyl blocking, and C5 position stabilization are critically examined for their roles in preventing lignin condensation and mitigating downstream enzyme inhibition. Furthermore, we elucidate how surfactants modulate interfacial phenomena during hydrolysis, from shielding non-productive lignin adsorption sites to stabilizing enzyme conformation against shear and thermal stresses. Finally, the review outlines a roadmap for transitioning from empirical screening to the rational design of sustainable, multi-functional surfactants, emphasizing their integration into closed-loop biorefinery processes.