Extraction of bamboo cellulose via sequential hydrated alkaline-acidic deep eutectic solvent pretreatment

Abstract The extraction of cellulose from bamboo residues remains challenging because lignin and hemicellulose are strongly integrated within the fibre matrix. Green pretreatment using a two-step DES method allows efficient fractionation and selective valorisation of lignocellulosic components. In this study, we aimed to extract cellulose from bamboo residues by selectively removing lignin and hemicellulose using a sequential hydrated alkaline-acidic deep eutectic solvent (DES) method. The process involved an initial treatment with an alkaline DES prepared from choline chloride and monoethanolamine, followed by an acidic DES made from choline chloride and oxalic acid. Hydrated dual treatment improved cellulose recovery, yielding 64.8% cellulose compared to 39.1% in untreated bamboo. Fourier Transform Infrared (FTIR) spectroscopy confirmed effective chemical fractionation through the disappearance of hemicellulose and lignin-associated peaks. Scanning electron microscopy (SEM) images showed that cellulose fibres extracted via dual-DES treatments exhibited network-like structures with widths of 20–30 μm. Thermogravimetric analysis (TGA) results also confirmed the efficient removal of non-cellulosic components, with 10.4% residue left compared to 20.8% for the untreated bamboo. Overall, these findings show that sequential hydrated DES pretreatment improved cellulose extraction and offers a sustainable route for processing bamboo biomass.