In this work, an efficient and green strategy for selective extraction and high-value utilization of lignin was proposed. Most of the hemicellulose in the feedstock was first removed by alkaline pretreatment to create a favorable structural environment for subsequent lignin dissolution. Subsequently, an acid-alcohol deep eutectic solvent (DES) system based on FeCl₃-ethylene glycol (FeCl₃-EG) was developed to achieve efficient and selective lignin dissolution. The results of characterization by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) showed that the lignin was removed significantly after the treatment, the cellulose structure was preserved, and the crystallinity and specific surface area were increased to 73.46% and 2.764 m²/g, respectively. The highest delignification rate of 96.53% was achieved when EG:FeCl₃ = 1:0.3. Gas chromatography-mass spectrometry (GC-MS) detected a variety of low molecular phenolic products. In-situ Raman spectroscopy revealed the dynamic process of lignin dissolution from the cell wall. The regenerated lignin was systematically characterized by FTIR, thermogravimetry (TG), elemental analysis, and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance (2D HSQC-NMR), and it was found that as the FeCl₃ content in DES increased, the β-O-4 content decreased, and the thermal stability of lignin increased. The pyrolysis properties were further analyzed by in-situ infrared (IR) spectroscopy, pyrolysis gas chromatography-mass spectrometry (Py GC-MS), and U-tube device, which showed that the regenerated lignin pyrolysis products had a high yield of the liquid phase and good phenol selectivity (40.94%), which demonstrated good selectivity and application prospects. This study provides a theoretical basis and process reference for the green extraction of lignin and its platform compound conversion.

In this study, three kinds of rough-wrought hemicelluloses (RHCs) were obtained via alkali extraction on different raw materials. One was untreated Phyllostachys edulis powder; the second was obtained via benzyl alcohol extraction of Phyllostachys edulis powder; and the third was holocellulose of Phyllostachys edulis powder. Carboxymethyl hemicelluloses (CMXs) were prepared by the alkalization and etherification of RHCs and were used to enhance the tensile strength of household paper. The results demonstrated a synergistic effect between CMX and polyamide epichlorohydrin resin (PAE), and the addition of small amount of CMX (0.35 kg/t pulp) can significantly improve the dry and wet tensile indices of paper. Study results of CMX strengthening mechanism revealed that the addition of CMX can improve the retention of PAE, especially the fine fiber, due to the adsorption of charges. The use of CMX in paper not only saves production costs but also reduces the proportion of long fiber, which is beneficial to the closed circulation and treatment of white water.

Deinking is an important process in waste paper recycling process, and this study mainly focuses on the properties of the deinking agent and process optimization. DIA-30 prepared in our laboratory, and FS and LD, were the three representative deinking agents studied herein. Brightness, effective residual ink concentration (ERIC), dirt, macro-stickies, fiber loss during repulping, flotation, and washing processes were measured to evaluate the performance of the deinking agents and optimize process conditions. Each of the deinking agents exhibited different advantages: DIA-30 was optimal for deinking efficiency, brightness enhancement, as well as dirt and macro-stickies removal, whereas LD was optimal for ink removal during flotation process but performed poorly in terms of brightness enhancement. FS showed a relatively balanced performance compared to those of DIA-30 and LD in the deinking process, but DIA-30 is the best option for deinking due to its outstanding comprehensive properties. The optimal repulping conditions for the deinking of 100% old magzines (OMG) using DIA-30 are as follows: repulping temperature, 60℃; pulp consistency, 13 wt%; repulping time, 20 min; H₂O₂ dosage, 0.5 wt% (oven-dried pulp); NaOH dosage, 1.2 wt% (oven-dried pulp); Na₂SiO₃ dosage, 0.3 wt% (oven-dried pulp); and optimum DIA-30 dosage, 0.1 wt%.

This paper summarizes the possible application of lignin extraction from black liquor and the development of lignin extraction technology. Lignin extraction from black liquor is an important, economical method to resolve the bottleneck associated with the recovery boiler and achieve the targeted capacity expansion in pulp mills. A few of key issues must be taken into cosideration when lignin extraction technology is adopted on the industrial scale.