Controlled Synthesis of Smaller than 100 nm Lignin Nanoparticles in a Furnace Aerosol Reactor

Lignin, a constituent of biomass, is a byproduct waste of the pulp and paper industry that may have several potential applications in nanoparticle form. Conventional synthesis of lignin nanoparticles (LNPs) involves physicochemical batch and multistep processes. We report here a continuous and single-step process for the synthesis of LNPs in a furnace aerosol reactor (FuAR) starting from bulk powders with minimal use of solvents. The synthesized LNPs were analyzed for their size distribution and functional group composition. Based on the changes in functional groups, the maximum temperature in the FuAR for obtaining LNPs without significant chemical degradation was found to be around 300 °C at a residence time of 5.8 s. The as-produced LNPs had a geometric mean diameter between 50 and 68 nm. Furthermore, the bulk and as-synthesized LNPs were tested for UV protection applications. The observed improvement in UV protection with a decrease in lignin particle size is systematically investigated using the optical absorption parameter, which provides a quantitative correlation for the effect of lignin particle size and mass concentration on UV protection performance. Overall, this study contributes to advancing lignin valorization by demonstrating the synthesis of LNPs using the scalable FuAR method and providing a novel quantitative correlation for the design of high-performance lignin-based UV protection materials.