Assembly of Organosolv Lignin Residues into Submicron Spheres: The Effects of Granulating in Ethanol/Water Mixtures and Homogenization

The production of chemicals and various materials from black liquor lignin will greatly improve the economics of biomass refining. In the present work, organosolv lignin residues (OLRs) from the organosolv pulping process were used to fabricate submicron lignin spheres using ethanol/water mixtures as an antisolvent, in conjunction with homogenization. Both the ethanol content in the ethanol/water mixture and the applications of homogenization were investigated as key factors affecting the agglomeration of OLRs. The results show that the solubility of the amphiphilic OLRs in ethanol was approximately 28 and 32 times greater than those of alkali lignin and kraft lignin, respectively. Using the optimal percentage of ethanol together with homogenization enhanced the nucleation of lignin macromolecules, such that the colloidal spheres of OLR were spontaneously assembled via gradual hydrophilic–lipophilic aggregation. The resulting OLR colloidal spheres had a yolk–shell structure and a mean particle diameter of around 200 nm, when the ethanol content was 50% and the homogenization time was 15 min or more. This study demonstrates a simple means of utilizing OLRs to produce lignin-based spheres. The lignin spheres generated in this work are thought to have potential applications in many fields as porous carbon precursors for energy storage, sensitive functional materials, and controlled-release fertilizer carriers.