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

Abstract

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.