Efficient separation and extraction of lignin components is one of the key technical challenges in the utilization of plant-based biomass resources. Among them, the diazabicyclo solvents share the great potential for the dissolution and extraction of lignin from plant-based materials, due to their unique and adjustable molecular structures. This study aims to dissolve and extract the lignin from plant-based agricultural and forestry wastes. A diazabicyclo-based switchable solvent (SS) was also used with 1,8-Diazabicyclo [5.4.0] undec-7-ene (DBU), hexanol, and water. Exceptional potential of the SS was observed in various lignin dissolution. Its model compounds were efficiently obtained even at room temperature. Systematic evaluation revealed that there was an impressive dissolution capacity of 453.2 mg/g for the milled wood lignin (MWL) at 25 °C, thus far exceeding that of conventional solvents, such as methanol, ethanol, and deep eutectic solvents. Kamlet-Taft solvent parameters indicated that the high hydrogen bond basicity (β) and net basicity of the SS substantially contributed to lignin dissolution. Lignin and its model compounds served primarily as hydrogen bond donors, interacting with the strong hydrogen bond acceptor regions within the SS. The formation of strong hydrogen bonds and non-polar interactions (including π-π stacking) synergistically promoted the dissolution of lignin in SS. Once applied to biomass, the SS system achieved high dissolution rates of 90%~93% for the lignin extraction from wheat straw and poplar sawdust. Crucially, the extracted lignin retained its structural integrity. Fourier Transform Infrared Spectrometer (FTIR) and Two-Dimensional Heteronuclear Single Quantum Coherence Nuclear Magnetic Resonance (2D HSQC NMR) analysis revealed that the cleavage of carbonyl (C=O) groups and the formation of α-O-R linkages occurred during the SS treatment. These α-O-R linkages were further hydrolyzed into α-OH, which facilitated the solubility in solvents. The crucial β-O-4 linkages remained intact, thus preserving the native aromatic framework. Gel Permeation Chromatography (GPC) further showed that the regenerated lignin shared a more uniform molecular weight distribution (PDI of 1.56 for poplar and 1.52 for wheat straw), compared with the conventionally extracted lignin. Consequently, the lignin significantly enhanced the solubility in both aqueous and organic solvents. For instance, the poplar lignin solubility in water increased from nearly to 205.68 mg/g, and its solubility in diethyl ether surged from 30.25 to 592.56 mg/g. Wheat straw lignin solubility in diethyl ether similarly increased from 45.21 to 492.05 mg/g. The structural modifications were induced by the SS treatment. In summary, the diazabicyclo-based SS served as a sustainable and effective solvent for lignin extraction. The lignin was efficiently dissolved under mild conditions. The core structural integrity of lignin was then retained for the β-O-4 linkages—downstream functionalization. Mechanistic analysis showed that only the α-carbonyl (C=O) and α-ether bonds were selectively disrupted to produce the lignin stream with a uniform molecular weight distribution, indicating the high solubility in polar solvents. This finding can provide the technical pathway for the separation, extraction, and high-value utilization of lignin from agricultural and forestry residues. Future research can explore the catalytic conversion and high-value utilization of lignin, according to the structural features of the SS-lignin. The carbohydrate components can be expected to be fully utilized in the large-scale recovery of SS solvents.

Agricultural waste grasses can be reused to alleviate the shortage pressure of fiber feedstock in the pulping and papermaking industry. The pellet fuel can also be prepared with industrial solid wastes, such as fiber feedstock waste residues and pulping liquid wastes. Furthermore, sustainable and clean energy sources are required to realize resource utilization, with the ever-increasing shortage of fossil energy and the growing environmental issues. In this study, the combustion performance of the waste residues was evaluated on the different fiber feedstock from the pulping process. The waste residue-based pellet fuel of fiber feedstock was also prepared by compression molding. The granular fuel was characterized by thermogravimetry, scanning electron microscopy (SEM), X-ray diffractometer (XRD), and thermal analyzation-infrared gas generation combined instrument. A systematic investigation was made to explore the effect of pulping waste liquid on the combustion performance of pellet fuel. The results showed that the combustion performance of waste residue-based pellet fuel from grass fiber feedstock was slightly worse than that from wood fiber feedstock. The reason was that the grass fiber feedstock with a higher content of non-combustible impurities and lower fixed carbon content. There were relatively low combustion performance and short combustion time with a comprehensive combustion index of 0.92×10^-7 %²/(min²·℃³). The grass waste residue-based pellet fuels were agglomerated lime-ash and blocked after combustion, which was different from wood waste residue-based pellet fuel. The alkali metal and silicon element in the waste residue-based pellet fuel from grass fiber feedstock were reacted at high temperatures, and then produced the slagging metal silicate particles ash containing SiO₂, Na₂Si₂O₃, and K₆Fe₂O₅ metal salt oxides. The high content of non-combustible impurities of grass waste residue-based pellet fuel led to the incomplete combustion of fixed carbon, which increased the CO gas composition in the combustion emission. In order to improve the combustion performance of wheat straw waste residue-based granular fuels, the mixture of pulping waste liquid/wheat straw waste residue with a solid content of 10.28% was compressed to prepare pellet fuel. The pulping waste liquid had high output after the pulping process, including a lot of organic matter, such as lignin and hemicellulose. Moreover, the lignin and sugars can be expected to serve as the natural adhesive in the granular fuels, in order to improve the combustion performance and mechanical strength of grass waste residue-based granular fuels. Furthermore, the pulping waste liquid was added to bind the solid waste for stability. The comprehensive combustion index and combustion activation energy of granular fuels from the mixture of pulping waste liquid/wheat straw waste residue was 2.50×10^-7 %²/(min²·℃³) and 59.88 kJ/mol, respectively. Correspondingly, the combustion index increased by 171.74%, whereas, the combustion activation energy decreased by 22.72%, compared with the pure wheat straw waste residue-based pellet fuel. The combustion performance was outstandingly improved in the wheat straw waste residue-based pellet fuel. The finding can provide the theoretical reference for the high-value utilization of agricultural waste plant fiber and resource utilization of solid wastes in pulping and papermaking.

Recently, cellulose nanofibril (CNF) has emerged as a promising, sustainable reinforcement with outstanding potential in material science. Owing to the properties of CNF, it has been explored in food, cosmetic, and pharmaceutical applications, as well as in industrial applications such as paints, drill muds, packaging, and papermaking. The application of CNF in papermaking is expected to be implemented in the near future to broaden the commercial market of cellulose. Numerous studies and patents have reported on the manufacturing, properties, and applications of nanocellulose. This present paper focuses on the recent progresses in the application of CNF as a wet-end additive in papermaking.

The components of the effluent from the chemical pretreatment of poplar alkaline peroxide mechanical pulp(APMP) were analyzed in this study. The main dissolved organics were low-molecular weight(LMW) lignin, oligosaccharides, and monosaccharides. The lignin and sugar concentrations in the effluent obtained using different chemical pretreatment conditions and chemical dosages were analyzed using ultraviolet(UV) spectroscopy. This analysis provided a theoretical basis for the subsequent treatment and utilization of APMP effluent. The experimental results showed that the dosages of NaOH, H₂O₂, and Na₂SiO₃ in the chemical pretreatment process affected the lignin and sugar concentrations in the effluent and that different chemicals had differing degrees of influence. The degree of influence exhibited the following order: NaOH > H₂O₂ > Na₂SiO₃. More specifically, the dosages of NaOH and H₂O₂ had stronger influences on the lignin and sugar concentrations than that of Na₂SiO₃. Indeed, the Na₂SiO₃ dosage hardly affected the lignin and sugar concentrations in the effluent, but Na₂SiO₃ could stabilize the chemical pretreatment system and improve the reactive efficiency of NaOH and H₂O₂. The pretreatment temperature and time also affected the organic components, and the influence of the temperature was stronger than that of time.