Structural characterization of lignin fractionated by acidic deep eutectic solvents and fabrication of lignin nanoparticles from Camellia Oleifera shell

Camellia oleifera shell (COS) is a waste biomass resource and abundant in lignin. Effective fractionation and valorization of lignin is of great significance. In this work, choline chloride (ChCl) and allyl trimethylammonium chloride (ATMAC) as hydrogen bond acceptors, and lactic acid (LA), acetic acid (AA) and oxalic acid (OA) as hydrogen bond donors were used to prepare six different acidic deep eutectic solvents (DES). The lignin was fractionated from COS by microwave-assisted method using acidic deep eutectic solvents, and lignin nanoparticles (LNPs) were further fabricated by self-assembly strategy. The structural characteristics of lignin and LNPs were analyzed and compared. The results demonstrated that ATMAC-LA pretreatment exhibited the highest delignification of 81.41% and cellulose retention of 95.1%. The molecular weight of lignin extracted from ChCl-based DES was lower than those obtained by ATMAC-based DES when using identical hydrogen bond donors. The smallest average particle size (203.07 nm) of LNPs was obtained by ATMAC-AA pretreatment. In addition, ATMAC-LA exhibited the highest interaction energy of 56.1 kcal/mol and stronger electrostatic potential (−46.72–54.58 kcal/mol), which elucidated its high delignification efficiency. ATMAC-LA DES exhibited high selectivity for lignin dissolution, and LNPs with smaller particle size and excellent stability could be fabricated. This work provides an efficient method to fractionate lignin from COS at 150 ℃ for 15 min, and contributing to extend the opportunities of lignin valorization into bio-based materials.