Green wood pulping processes with high pulp yield and lignin recovery yield by deep eutectic solvent and its aqueous solutions

The development of innovative processes for eco-friendly, yet efficient, wood pulping is required to achieve higher sustainability than traditional processes. In this study, the potential use of deep eutectic solvent (DES) and its aqueous solutions as delignification medium for eucalyptus pulping is evaluated. The effects of temperature and water content in the DES on the pulping process were investigated. Additionally, traditional kraft pulping was performed as a reference. The integration of water into DES could facilitate delignification and preserve carbohydrates, and the optimal result of choline chloride-lactic acid (ChCl-LA) aqueous solution with 20 vol% water pulping process achieved the highest pulp yield (60.11 +/- 0.29%) with a lignin removal of 87.59 +/- 0.78% at 140 degrees C. Further analysis revealed that the obtained pulp with a degree of polymerization of 1498 and a crystallinity of 69.79% exhibited better physical properties than kraft pulp. Meanwhile, 80.11 +/- 0.80% of the initial lignin in wood with lower condensation degrees, more homogeneous molecular weight distribution, and higher purity than kraft lignin was recovered by sample precipitation with water. This study indicates that ChCl-LA aqueous solution (20 vol% water) is the potential wood pulping system and provides a great reference for the sustainable development of the pulp and paper industry.