Limonene-modified lignin nanoparticles functionalized via aqueous thiol-ene grafting

Lignin nanoparticles offer a renewable platform for functional nanomaterials; however, strategies that introduce reactive functionality while preserving self-assembly and colloidal stability remain limited. Here, softwood kraft lignin was functionalized with limonene oxide to introduce hydrophobic alkene-bearing side chains while preserving amphiphilicity required for nanoparticle formation. Controlled epoxide ring opening enabled selective modification of phenolic hydroxyl groups, while retaining terminal alkene functionality for post-assembly reactions. Limonene incorporation reduced nanoparticle hydrodynamic diameters upon solvent shifting. ζ-potential analysis indicated preserved colloidal stability and suggested the formation of a limonene-enriched hydrophobic core with a polar shell. The accessible alkene groups enabled UV-mediated thiol-ene functionalization of preformed nanoparticles. Thiol structure dictated colloidal response. Particularly, dithiolthreitol induced partial interparticle association, cystamine promoted extensive aggregation, and dithiol-poly(ethylene glycol) provided steric stabilization, resulting in an increased hydrodynamic size. This work demonstrates a modular strategy to decouple lignin backbone modification from surface functional diversification while maintaining nanoparticle integrity.