Fractionation of alkali lignin by organic solvents for biodegradable microsphere through self-assembly.

• Multi-grade lignin can be obtained by solvent fractionation. • Different organic solvents have different proportions of dissolved lignin. • Lignin fractions have different physicochemical properties and hydroxyl content. • Microsphere with different surface morphologies was prepared from lignin fractions. Here we report a centrifugation-based fractionation methodology that was integrated with three types of organic solvents to fractionate industrial alkali lignin toward the fabrication of lignin microsphere. The Fourier-transform infrared spectroscopy (FT-IR) result showed that the chemical structure of lignin was not changed by solvent fractionation. Soluble lignin in each solvent had lower molecular weight, improved polydispersity index (PDI) and less impurities (S, N), while insoluble lignin had a high bio-char yield and can be utilized as potential carbon source for porous carbon nanosphere materials. In addition, well-shaped lignin microsphere with smooth or anisotropic surface can be prepared by selecting proper lignin fraction without any chemical modification. This work thus provides a new strategy for the derivation of lignin as raw materials for value-added products, which paved a new way to develop a green and sustainable bio-refining industry. [ABSTRACT FROM AUTHOR]