Direct dissolution and regeneration of cellulose-rich solid fractions from microwave-assisted deep eutectic solvent-treated spruce wood into cellulose fibers via DMAc/LiCl

The modern complex biorefinery concept targets maximum utilization of all wood constituents. In our work, after non-cellulose carbohydrates (hemicellulose and pectin) and lignin components were sequentially isolated from spruce wood, approximately the remaining residual cellulose-rich solid fraction (CSF) accounted for half of the wood in mass balance. The high cellulose content of CSF makes it a promising source for producing high-value regenerated cellulose fibers (RCFs). In this study, RCFs were successfully prepared from different non-bleached CSF samples via wet spinning in an N, N-dimethylacetamide/lithium chloride (DMAc/LiCl) solvent system. Specifically, CSFs from microwave-assisted deep eutectic solvent (MW-DES) fractionation and hot water extraction followed by MW-DES (HWE-MW-DES) fractionation processes were comparatively investigated to understand their correlation with mechanical and thermal properties of RCFs. Low molar mass and reduced hemicellulose residue in CSFs in the carbohydrate-first fractionation (HWE-MW-DES) process are emphasized as key factors in enhancing the elongation and toughness of manufactured RCFs. The obtained results offer a promising pathway for valorizing CSFs into high-performance RCFs, maximizing the value of proposed biorefinery concepts.