Study on Thermally Induced Lignin Aggregation Kinetics\nfor the Preparation of Uniformly Sized Lignin Nanoparticles in Water

Lignin\nnanoparticles (LNPs) present a potential avenue for the\nhigh-value utilization of lignin. However, the simple and ecofriendly\nmethod of thermally induced self-assembly for the preparation of LNPs\nhas been overlooked due to a lack of sufficient understanding of the\nlignin aggregation mechanism. Therefore, this study focuses on the\nkinetics of thermally induced lignin aggregation. It was found that\nlignin aggregates formed at lower temperatures exhibit poor stability\nand are more prone to continuous growth through coalescence. This\napparent contradiction with the conventional understanding of thermoresponsive\npolymers could be attributed to changes in the viscoelasticity of\nthe lignin aggregates during phase separation. Based on this finding,\nwe worked out strategies to optimize the preparation of LNPs in water\nthrough thermally induced self-assembly. Pure LNPs with well-defined\ninterfaces and a minimum polydispersity index (PDI) of 0.12 were obtained\nby increasing the temperature to 125–150 °C. Furthermore,\ncombined with noncovalent modification, LNPs with a PDI of 0.08 would\neven be formed at 80 °C. Notably, the resulting pure LNPs show\npotential for application in photonic crystal products that require\nexcellent monodispersity. This study provides a new approach for the\nenvironmentally friendly preparation of LNPs with a controllable morphology.