Comparing the improvement of enzymatic hydrolysis effect of Celtis sinensis leaves residue by hydrophilic or hydrophobic deep eutectic solvent pretreatment

This study used deep eutectic solvents (DES) to extract the active components from Celtis sinensis leaves, with the residue comprising at least 90% of the total biomass. The main components included cellulose, hemicellulose, and lignin, representing a renewable lignocellulose resource. In recent years, DES has attracted considerable attention in the field of biomass pretreatment due to its straightforward preparation methods, cost-efficiency, and ease of recovery. Therefore, DES may be an effective method for lignin separation. This study analyzed the compositional changes in different types of DES-extracted residues and compared the hydrophilic and hydrophobic DES extraction methods for the enzymatic hydrolysis of cellulose in Celtis leaves. The results showed that hydrophilic DES was more competitive during decomposition. Pretreatment reduced the lignin from 37.55 to 22.18%, while the cellulose levels displayed a minimal decline from 19.94 to 16.45%. Therefore, DES effectively removed lignin and hemicellulose from the leaves, while retaining most of the cellulose in the specified conditions. Furthermore, scanning electron microscopy (SEM) was used to characterize the surface morphology changes in the original leaves and residues pre-treated with different solvents. The influence of chemical structural changes on the subsequent enzymatic hydrolysis was investigated further via thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). Compared to hydrophobic DES, hydrophilic DES effectively removed amorphous components such as hemicellulose and lignin from the extracted residue, which improved cellulase hydrolytic efficiency. The results confirmed that the crystal structure of cellulose in the extraction residue displayed no changes, while the relative crystallinity increased. The rate and degree of the subsequent enzymatic glycation were enhanced, while the hydrolytic efficiency of hydrophilic DES increased 2.13-fold (40.19 similar to 85.86%).