Production and characterization of lignin containing nanocellulose from luffa through an acidic deep eutectic solvent treatment and systematic fractionation

In this study, lignin and hemicelluloses were partially separated from non-wood biomass of luffa sponge using an acidic deep eutectic solvent (ADES) composed of choline chloride and oxalic acid dihydrate, and the obtained cellulose-rich residue was further disintegrated into lignin containing cellulose nanocrystal (OA-CNC) and nanofiber (OA-CNF) fractions with a two-step ultrasonication treatment. The ADES had a dual purpose: to produce fractions of biomass and to accelerate the nanofibrillation of cellulose. Under optimal reaction conditions (at 90 °C for 150 min), solid fractions with cellulose content of 76.4 wt% (initially 51.8 wt%) and residual lignin content of 10.7 wt% (initially 17.8 wt%) were achieved. Ultrasonication resulted in lignin containing nanocelluloses with a high total yield (59.1 wt% vs. 50.5 wt% from reference 60% sulfuric acid hydrolysis). They consisted mainly of elongated cellulose nanofibers (OA-CNF) with an average diameter of 28 nm. The OA-CNF were further converted to flexible and foldable self-standing films with tensile strength of 134 MPa and elongation at break of 10.6%. This simplified method also presents great potential for using biomass waste (e.g., wheat straw, branches, and sawdust) to produce lignin containing nanocellulose.