Facile preparation of lignin nanoparticles from waste Camellia oleifera shell: The solvent effect on the structural characteristic of lignin nanoparticles

This study investigated the water-organic co-solvent for the fractionation of lignin in camellia oleifera shell and further fabrication of lignin nanoparticles (LNPs). The highest dissolution (88.6 wt%) of lignin was obtained in H2O/GVL (3/7, v/v) co-solvent, which was mainly ascribed to the adjacent Hildebrand solubility parameter (δ) between lignin and co-solvent. The LNPs prepared by solvent-shifting method and precipitation exhibited round or oval shape with even distribution. Among which, LNPs obtained from the lignin fraction dissolved in H2O-ethanol co-solvent (denoted as LNP-ETH) showed the smallest average particle size of 136 nm and the highest negative zeta potential of − 39.6 mV, which implied the relatively stable lignin nanoparticles prepared from H2O-ETH co-solvent. The structural analysis of lignin nanoparticles revealed that LNPs maintained the lignin aromatic skeleton, C-O-C/C-C linkages and basic structural units (G, S and H). So far, this research offered great potential for the preparation of lignin-based materials from abundant forestry waste camellia shell.