Synthesis of lignin nanoparticles using CO₂-responsive amines and their performance as UV-light shields

Lignin is biosourced, abundant, biodegradable and renewable, and therefore an appealing feedstock from which to make materials for applications in diverse fields. In this work, we report the initial results of a new method to produce lignin nanoparticles (LNP) with tailored particle size. Lignin is first dispersed at elevated pH in an aqueous solution of a CO₂-responsive amine, after which the addition of CO₂ at atmospheric pressure induces precipitation of the lignin as nanoparticles. Two different CO₂-responsive amines, TMBDA (N,N,N',N'-tetramethyl-1,4-butanediamine) and TMTAD (2,6,10-trimethyl-2,6,10-triazaundecane), were evaluated for their effect on the lignin particle size and yield. For both amines, particle sizes were in the range of 125-175 nm with narrow particle size distributions. Yields were >84% for TMBDA and >94% for TMTAD. These LNP, when dispersed in poly(vinyl alcohol) (PVA) films, provide promising UV blockage even at low LNP content.