An eco-friendly strategy for preparing lignin nanoparticles by self-assembly: Characterization, stability, bioactivity, and Pickering emulsion

Spherical lignin nanoparticles (LNPs) offer more possibilities for high value-added use of lignin, but un-ecofriendly organic solvents used for preparing LNPs must be addressed. This study reported a green and simple method to produce LNPs using a betaine:lactic acid deep eutectic solvent (DES) via self-assembly induced by dropping water. The critical water content (41 vol%) at the beginning of self-assembly was determined by dynamic light scattering. The well-defined spherical colloid particles with an average size of 57.16 ± 1.43 nm were obtained after adding 80 vol% water content, followed by verifying the morphologies via scanning electron microscopy and transmission electron microscopy. A better water dispersibility of colloid particles was elucidated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The stable LNPs were optimized at 5 mg/mL of initial lignin concentration, 1 mL/min of dropping speed, and 80 vol% water content. Compared with lignin, LNPs exhibited improved thermal stability, enhanced antioxidant activity, and lower minimum inhibitory concentration against Staphylococcus aureus (4.0 mg/mL). Further, 7.5 mg/mL of LNPs concentration demonstrated its potentiality as a stabilizer in Pickering emulsions. Furthermore, the produced LNPs displayed high potential in bio-based materials and emulsion, providing a critical foundation for broadening the further utilization of lignin.