Choline chloride – oxalic acid dihydrate deep eutectic solvent pretreatment of Barley straw for production of cellulose nanofibers

This study investigates the production of cellulose nanofibers (CNF) from Barley straw using ultrasound-assisted deep eutectic solvent (US-DES) treatment for biomass fractionation and subsequent high-intensity ultrasonication (HIUS) for nano-fibrillation. Two deep eutectic solvents (DES), synthesized from choline chloride (ChCl) and oxalic acid dihydrate (OAD) at 1:1 and 2:1 M ratio, achieved solubilisation of over 80 % of lignin and hemicellulose under optimal conditions. The purification of these DES-treated materials resulted in cellulose with a purity >88 %. CNFs, characterized by a size of <100 nm, a polydispersity index under 0.5, and a zeta potential lower than -30 mV, were successfully isolated through a combination of wet grinding and HIUS treatment. SEM and XRD results showed the formation of a network of interconnected fibres with a Type I cellulose structure. This research highlights Barley straw's potential as a sustainable source of high-value CNF from agricultural waste.