Organic solvent-free production of colloidally stable spherical lignin nanoparticles at high mass concentrations†
Lignin nanoparticles have emerged during the past decade as well-defined and renewable nanomaterials for fundamental and applied research. However, the presently known methods for the preparation of lignin nanoparticles rely on the use of organic solvents and energy intensive water evaporation processes. Here we present organic solvent-free production of spherical lignin nanoparticles by neutralization of alkaline solution of poorly water-soluble lignins in the presence of sodium lignosulfonate. We show that by combining these two predominant technical lignins it is possible to achieve colloidally stable lignin nanoparticle dispersions at concentrations exceeding 30 wt%. We further demonstrate versatility of the process by using ethanol organosolv lignin, soda lignin, and lignosulfonates from different sources. The lignin nanoparticle dispersions exhibit shear-thinning behaviour and undergo gelation within well-defined pH and concentration regions. Such flowable lignin dispersions mark a breaktrough towards scalable processing of lignin towards sustainable bio-based chemicals and materials.