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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]

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]