Binary mixture of subcritical water and acetone: a hybrid solvent system towards the production of lignin nanoparticles

Valorization of technical lignin is crucial for the circular bioeconomy – this can be achieved by the transformation of lignin to high-value nanomaterials. However, the majority of lignin nanoparticle (LNP) production methods require high volumes of organic solvent, and specialized equipment, or fail in certain cases to produce a morphologically uniform product with superior physicochemical properties to technical lignin. Herein, a binary solvent system of subcritical water and acetone based on the principles of solvent–antisolvent (SAS) precipitation of lignin is proposed. Spherical LNPs with a high degree of uniformity in the chemical structure are produced via a batch reactor from kraft lignin demonstrating high yield (88–92%), colloidal stability in water, thermal stability, and low mean particle size – these are desirable for advanced biocomposite and biomedical applications; achieved in this study by using lower volumes of recyclable acetone (4–7 times less) than previously reported.