Acidic and alkaline deep eutectic solvents pretreatment of Macadamia nutshells for production of cellulose nanofibrils and lignin nanoparticles

This study explored a facile method for converting macadamia nutshells into bio-based nanomaterials, including cellulose nanofibers (CNFs) and lignin nanoparticles (LNPs), through deep eutectic solvent (DES) pretreatment coupled with a nanofabrication strategy. Comparisons of the physicochemical, morphological, and structural properties of the CNF and LNPs produced through acidic choline chloride/oxalic acid dihydrate (ACDES) and alkaline K 2 CO 3 /glycerol DES (ALDES) pretreatments were conducted using SEM, TEM, FTIR, XRD, TGA, GPC and 2D NMR. The CNFs obtained from ACDES pretreatment (ACCNFs) exhibited uniform and long filament-like structures with shorter whisker-like nanocrystals. Conversely, the CNFs produced with the ALDES pretreatment (ALCNFs) displayed irregular aggregates and nanofibril bundles. Additionally, the ACCNFs demonstrated higher crystallinity and contained small amounts of the oxalate half-ester compare to ALCNFs. During ACDES pretreatment, a large proportion of β-O-4, β-5, and β-β linkages in lignin disrupted and re-condensed to form lignin substructures, resulting in the assembly of cluster-like lignin nanoparticles pretreated with ACDES (ACLNP) aggregates. In contrast, lignin nanoparticles pretreated with ALDES (ALLNP) exhibited uniform nanospherical shapes because of the preservation of β linkages in lignin during the ALDES pretreatment. This work not only broadens the fabrication strategies for CNF and LNPs but also offered a promising approach for the valorization of lignocellulosic agricultural wastes.