Direct production of lignin nanoparticles (LNPs) from wood using p-toluenesulfonic acid in an aqueous system at 80°C: characterization of LNP morphology, size, and surface charge

Lignin nanoparticles (LNPs) from renewable lignocelluloses can be a valuable building block for a variety of applications and could contribute to the economic development in rural agricultural communities. Current technologies for producing LNPs are not cost effective and use toxic solvents. In this study, LNPs were produced by fractionating poplar wood at ≤80°C with a recyclable hydrotrope p-toluenesulfonic acid (p-TsOH) in an aqueous system. The dissolved lignin was separated as LNPs simply by diluting the spent liquor (SL) to the minimal hydrotrope concentration (HCmin) of 11.5%. The p-TsOH, a solid acid, can be easily recycled by re-concentrating the diluted SL after lignin separation. The LNP size, morphology, and surface charge were controlled by the dilution ratio, speed, pH, and ionic strength of the LNP sol. The LNPs were analyzed by dynamic light scattering (DLS) and found to be fairly stable in terms of mean particle size and surface charge over a period of 2 weeks. Fractionation conditions also affected LNP properties.