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Nanocellulose has attracted attention from the scientific community due to its biodegradability and unique physiochemical characteristics. However, the production of high-quality nanocellulose is still limited by the high cost of chemical usage, purification, and energy consumption. In this work, we proposed a catalytic aerobic process for preparing aldehyde-functionalized cellulose nanocrystals by oxidizing cellulose in a triisopropoxy vanadium (VO(OiPr)3)/O2 system and investigated the mechanism of selective oxidation of cellulose in this system. Well-dispersed cellulose nanocrystals with a diameter of approximately 100 nm and an aldehyde content of 0.425 mmol g−1 were obtained under the conditions of 120 °C, 4 MPa O2 pressure, and a 12 h reaction time. The catalyst employed in the oxidation process still retained high activity after being reused four times. This research presents an alternative strategy for the preparation of cellulose nanocrystals with limited chemical usage, which would contribute to the development of environmentally friendly and cost-effective processes for nanocellulose production. [ABSTRACT FROM AUTHOR]

Lignin is a phenolic polymer, making it a sustainable alternative to phenol for synthesizing lignin–phenol–formaldehyde (LPF) adhesives. However, technical lignins produced in pulping or biorefining processes are generally highly condensed and have low reactivity, limiting their uses in synthesizing phenolic-based adhesives. Herein, we report a two-step strategy to produce lignin-based wood adhesives with industrially available technical lignins through hydrodeoxygenation followed by acid-mediated methylolation of aromatic C2/6 positions to improve the flowability, water resistance, and crosslinking ability of lignins. We demonstrated that this biobased lignin–formaldehyde adhesive had a lighter color and far better adhesion performance compared to traditional LPF resins prepared from base-mediated methylolation of lignins. Mechanistic investigation suggests that the chemical crosslinking of methylolated lignin to form diarylmethane structures and the physical interlocking interaction at the interfaces of wood veneers contribute to the strength of plywood. [ABSTRACT FROM AUTHOR]

Kraft lignin, the principal by‐product of the pulping industry, is an abundant yet highly underutilized aromatic resource. It is useful due to the vast scales involved as a source of fuels, chemicals, and functional materials when suitable postprocessing is applied. It is deemed to be a renewable alternative to fossil sources. Because of the extreme complexity of kraft lignin, in‐depth composition analysis and chemical structural identification are crucial for the development of effective valorization strategies. This work embarks on the characterization and identification of lignin‐derived phenolic compounds in representative hardwood (Eucalyptus) kraft lignin after selective fractionation using a single solvent. Advanced 2D heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR), 31P NMR, and mass spectrometry in combination with synthetic authentic compounds are used for the structural identification of the low‐molecular‐weight fraction of kraft lignin. A total of 20 phenolic compounds, including several novel monomers (catechols), dimers (diarylethanes, diarylethenes, etc.), and trimers with triphenyl structures are systematically identified in the Eucalyptus kraft lignin. In addition, polysulfide is detected in the low‐molecular‐weight fraction, indicating that the oxidative polymerization of S2−/HS− occurrs during the kraft pulping process. An improved understanding of kraft lignin, especially the low‐Mw fraction, is expected to provide essential information for the selective fractionation and valorization of lignin. [ABSTRACT FROM AUTHOR]

Lignin is a renewable and the most abundant aromatic source that can be used for extensive chemicals and materials. Although approximately 50 million tons of lignin are produced annually as a by-product of the pulp and paper industry, it is currently underutilized. It is important to know the structural features of technical lignin when considering its application. In this work, we have demonstrated the formation of low-molecular-weight constituents from hardwood (Eucalyptus) lignin, which produces much more low-molecular-weight constituents than softwood (spruce) lignin, after a chemical pulping process, and analyzed the micromolecular compositions in the alkali lignin after fractionation by dichloromethane (DCM) extraction. By applying analytical methods (gel-permeation chromatography, 2D NMR and GC-MS) with the aid of evidence from authenticated compounds, a great treasure trove of lignin-derived phenolic compounds from Eucalyptus alkali lignin were disclosed. Except for some common monomeric products, as many as 15 new lignin-derived monomers and dimers including syringaglycerol, diarylmethane, 1,2-diarylethanes, 1,2-diarylethenes, (arylvinyl ether)-linked arylglycerol dimers and isomeric syringaresinols were identified in the DCM-soluble fraction. Regarding the formation and evolution of the Cα-condensed β-aryl ether structure, a novel route that is potentially responsible for the high content of β-1 diarylethenes and diarylethanes in the lignin low-molecular-weight fraction, in addition to the β-1 (spirodienone) pathway, was proposed. This work not only provides novel insights into the chemical transformation of S–G lignin during the alkali pulping process, but also discovered lignin-derived phenolic monomers and dimers that can potentially be used as raw materials in the chemical or pharmaceutical industries. [ABSTRACT FROM AUTHOR]

Soda process is one of the most important pulping processes in paper industry producing large quantities of alkali lignins that can afford plenty of biofuels, aromatic chemicals and materials. However, the structural and size-related heterogeneities and complexities hinder the development in these directions. Herein, we report new insights into the structure of alkali lignin, through investigating the formation and transformation of enol ether and arylglycerol structures that are significant responsible for the structural transformation from native lignin to alkali lignin. Four-type enol ethers composed of G/S units in hardwood alkali lignin were identified by 2D HSQC NMR. A series of alkali lignins prepared by alkali treatment of eucalyptus cellulolytic enzyme lignin under various temperatures were analyzed by 2D HSQC NMR, 31P NMR and gel permeation chromatography (GPC). Upon these analyses and related model compound studies, it was found that the arylglycerols formed from native β-O-4 linkages tends to be oxidized with the further degradation of aryl ether bonds, and that the enol ether linkages are facile to be hydrolyzed or oxidized in the air. These insights improve the mechanistic understanding for the structural evolution and the diversity of alkali lignins and will aid the development of further lignin valorization strategies. Unlabelled Image • Alkali lignins from different-temperature treatment were analyzed by 2D HSQC NMR. • Various enol ether linkages composed of G/S units were assigned by 2D HSQC NMR. • The formation and further side-chain oxidation of arylglycerol structures were unraveled. • The degradation of enol ether linkages in air under room temperature was proved. [ABSTRACT FROM AUTHOR]

γ-valerolactone (GVL)/H2O/acid solvent mixtures has been used in chemical pretreatment of lignocellulosic biomass, it was claimed that GVL lignins were structurally close to proto (native) lignins, or having low molecular weight with narrow polydispersity, however, the structural changes of GVL lignins have not been investigated. In this study, β-O-4 (β-aryl ether, GG), β-5 (phenylcoumaran), and β-β (resinol) lignin model compounds were treated by an acidic GVL-H2O solvent system, a promising pretreatment of lignocellulose for biomass utilization, to investigate the structural changes possibly related to the lignin involved. NMR characterization of the products isolated from the treated GG indicated that a phenyl dihydrobenzofuran, having typical C-H correlations at δC/δH 50.74/4.50 and 93.49/4.60 ppm in its HSQC spectrum, was produced from GG. In the pretreatment, the released formaldehyde from GG reacted fast with GG to form a novel 1,3-dioxane intermediate whose characteristic HSQC signals were: δC/δH 94.15–94.48/4.81–5.18 ppm and 80.82–83.34/4.50–4.94 ppm. The β-5 model, dihydrodehydrodiconiferyl alcohol, was converted into phenylcoumarone and stilbene having benzaldehyde that resulted from the allyl alcohol side chain. The β-β model, syringaresinol, was isomerized to form a mixture of syringaresinol, epi-, and dia-syringaresinol although being degraded slightly. [ABSTRACT FROM AUTHOR]

Chinese Angelica is a significant medical plant due to the various therapeutic constituents in its root; whereas the aerial part is considered worthless and often discarded as agricultural waste. In this work, phytochemicals from the stem were first systematically analyzed by means of GC–MS after derivatization and HPLC–MS/MS in multiple reaction monitoring (MRM) mode. Phthalides, ferulic acid, and coniferyl ferulate were detected in the stem; although their content is relatively low in comparison with the root. Some specific compounds, such as p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, caffeic acid, 4-hydroxyphenyl-1, 2-ethanediol, thymol-β-d-glucopyranoside, etc. and a significant amount of phytosterols (1.36 mg/g stem, mainly β-sitosterol) were detected in the stem. The extracted oil from the stem contained a considerable amount of phthalides (48.5 mg/g), β-sitosterol (56.21 mg/g), and stigmasterol (14.03 mg/g); no other bioactive compounds were found that could be potentially used as pharmaceuticals or additives to healthcare food. [ABSTRACT FROM AUTHOR]

Lignin is recognized as a good sustainable material because of its great abundance and potential applications. At present, lignin hydrogenolysis is considered as a potential but challenging way to produce low-molecular-mass aromatic chemicals. The most common linkage between the structural units of lignin polymer is the β-O-4 aryl ether, which are primary or even only target chemical bonds for many degradation processes. Herein, a Pd-Fe3O4 composite was synthesized for catalytic hydrogenolysis of β-O-4 bond in lignin. The synthesized catalyst was characterized by XRD, XPS, and SEM and the lignin depolymerization products were analyzed by GC-MS. The catalyst showed good catalytic performance during the hydrogenolysis process, lignin dimer was degraded into monomers completely and a high yield of monomers was obtained by the hydrogenolysis of bagasse lignin. More importantly, the magnetic catalyst was separated conveniently by magnet after reaction and remained highly catalytically efficient after being reused for five times. This work has demonstrated an efficient & recyclable catalyst for the cleavage of the β-O-4 bond in lignin providing an alternative way to make better use of lignins. [ABSTRACT FROM AUTHOR]