Size-tailorable lignin nanoparticle synthesis: effects of solution chemistry and DLVO forces on amphiphilic balance of lignin

Abstract

Lignin nanoparticles (LNPs) have gained great interest as a promising renewable nanomaterial toward value-added applications. This work investigated solution chemistry and particle–particle interaction force in the LNP formation aiming at a facile technique to balance amphiphilic properties of lignin for size-controlled synthesis. By facilely tuning solution chemistry, lignin with different amphiphilic properties can form the nanoparticles with 57–262 nm and dispersity index (Đ) less than 0.2 at an initial lignin concentration of 10–80 g L⁻¹. A numerical estimation of particle size was established with Derjaguin–Landau–Verwey–Overbeek's (DLVO) theory and population balance equation (PBE) to evaluate the interaction energy of particles as the function of solution chemistry and lignin properties. In the developed DLVO–PBE model, lignin properties such as molecular weights and content of functional groups are closely related to the repulsive energy calculation in the particle collision and further determine the assembly patterns. The model can be applied to lignin with varied properties with high prediction accuracy, especially in the DLVO forces-driven aggregation. It also suggests that solvated lignin chains can involve the uneven electrostatic force field and non-DLVO forces leading to a broad/multi-modal size distribution. Overall, the combination of experimental and theoretical investigations provides new insights into assembly mechanisms of lignin molecules involved in the formation of nano-/submicron particles.