Lignin Nanoparticles: Green Synthesis in a γ-Valerolactone/Water Binary Solvent and Application to Enhance Antimicrobial Activity of Essential Oils

Lignin nanoparticles (LNPs), as a special aggregate of renewable and biodegradable lignin available in abundant amounts, are a perfect building-block material because of their advantages, including good dispersibility in water, great biocompatibility, and eco-friendly characteristics. To exploit a promising method of producing LNPs, we developed a simple and sustainable synthesis approach using a recycled γ-valerolactone (GVL)/water binary solvent (GWBS). Up to 200 g/L lignin from several sources could be completely dissolved in GWBS. LNPs were easily obtained through nanoprecipitation (dropping or dialysis) of the lignin solution. The yield and size of LNPs can be controlled during nanoprecipitation. The highest yield of LNP reached 90% via dropping nanoprecipitation, and its relevant initial concentration was up to 24 g/L. This highly efficient dropping method might provide a method for scaled-up production of LNPs. The resultant LNPs, having a diameter of ca. 250 nm and a ζ-potential of −40 mV, also showed good dispersibility and stability in water. LNPs can stabilize essential oils and promote their growth inhibition activity against microbes. These results indicated that we also initiated a new method of achieving enhanced antimicrobials with whole biomass-based chemicals.