Efficient fractionation of Chinese fir lignocellulose using acidified deep eutectic solvent with downstream valorization into value-added cellulosic nanofillers and propylguaiacol

Fractionation of softwood lignocellulose poses challenges due to its relatively high lignin content and complex interlinkages. In this study, an acidified deep eutectic solvent (choline chloride/ethylene glycol with 1 wt% AlCl₃) was employed to effectively fractionate Chinese fir chips into cellulose-rich and lignin fractions, achieving good to excellent yields. The cellulose-rich fraction was directly valorized into lignin-containing cellulose nanofibers (LCNFs) with a high yield. The prepared LCNFs were utilized as functional nanofillers in waterborne polyurethane wood coatings (WWC), resulting in an increase in tensile strength from 15.2 ± 0.35 MPa to 18.5 ± 0.43 MPa with the optimal addition of 0.5 wt% LCNFs. Furthermore, the addition of LCNFs significantly improved the coating properties, including hardness and wear resistance. The remaining lignin in the LCNFs imparted excellent optical properties to the WWC film, imparting a warm amber hue and improved texture convexity after coating. Analysis of the lignin fractions revealed a high total content of β-O-4 linkages. Following a catalytic hydrogen transfer depolymerization process, 9.8 wt% of propylguaiacol was obtained with near-quantitative selectivity. This study highlights the effectiveness of acidified deep eutectic solvents in the refinery of softwood lignocellulose, providing a novel pathway for the production of value-added bio-based nanomaterials and chemicals.