Integrated process for lignin depolymerization and nanoparticle production using deep eutectic solvent

Abstract

Abstract Lignin, the most abundant natural aromatic macromolecule, holds significant potential for high-value applications. However, its complex and irregular structure, along with challenges in efficient processing, has limited its widespread use. In this study, we propose an ecofriendly continuous process utilizing deep eutectic solvents (DESs) for lignin depolymerization and subsequent production of lignin nanoparticles. DESs, composed of choline chloride and lactic acid, effectively break down lignin into low-molecular-weight homogeneous fragments while also serving as a solvent for nanoparticle formation. The depolymerized lignin nanoparticles (DLNPs) exhibited a uniform particle size distribution and enhanced surface charge due to interactions with the DES, resulting in excellent long-term dispersion stability. Chemical analyses indicated that lignin depolymerization primarily involved the cleavage of β-O-4 linkages while retaining its aromatic structure and forming condensation products such as pinoresinol and phenylcoumaran. Thermal analysis revealed that DLNP produced through this continuous process displayed improved thermal stability compared to kraft lignin, suggesting potential applications in high-temperature environments, such as flame retardants. This study demonstrates that the DES-based process is a promising alternative to conventional organic solvent methods, providing a sustainable and efficient pathway for lignin nanoparticle production and valorization.