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An industrial alkaline lignin preparation and poplar particles were mixed and hot pressed under different conditions. The alkaline lignin and the lignin isolated from the poplar particles were thoroughly investigated by quantitative nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and elemental analysis techniques. For the first time, it was found that the content of β-O-4′ linkages decreased accompanying with the formation of β-β′, β-5′, and β-1′ linkages at mild heat treatment temperatures (130–170 °C). However, it should be noted that most of the β-O-4′, β-β′, β-5′, and β-1′ linkages nearly disappeared at a higher temperature (180 °C). Cross-linking reactions were predominant during the hot-pressing process as the molecular weight of lignin increased at elevated temperature. Owing to the self-bonding between lignin fragments during the hot-pressing process, a green poplar wood–lignin composite was successfully prepared with poplar particles and a small amount of alkaline lignin (∼20%, w/w). Internal bond strength with 0.47 MPa was surprisingly achieved under the conditions of pressing temperature 160 °C, pressure 5 MPa. An in-depth understanding of the concerted reactions between fragmentation and cross-linking reaction in lignin during hot pressing was beneficial to a better development of self-bonding green wood–lignin composites in future.

This study is aimed at achieving the optimum conditions of hydrothermal treatment and acetylation of Populus fiber to improve its oil sorption capacity (OSC) in an oil-water mixture. The characteristics of the hydrolyzed and acetylated fibers were comparatively investigated by FT-IR, CP-MAS 13C-NMR, SEM and TGA. The optimum conditions of the hydrothermal treatment and acetylation were obtained at 170 °C for 1 h and 120 °C for 2 h, respectively. The maximum OSC of the hydrolyzed fiber (16.78 g/g) was slightly lower than that of the acetylated fiber (21.57 g/g), but they were both higher than the maximum OSC of the unmodified fiber (3.94 g/g). In addition, acetylation after hydrothermal treatment for the Populus fiber was unnecessary as the increment of the maximum OSC was only 3.53 g/g. The hydrolyzed and the acetylated Populus fibers both displayed a lumen orifice enabling a high oil entrapment. The thermal stability of the modified fibers was shown to be increased in comparison with that of the raw fiber. The hydrothermal treatment offers a new approach to prepare lignocellulosic oil sorbent.

Eucalyptus grandis fibers were treated with hot-compressed water (HCW) and laccase mediator to enhance the fiber characteristics and to produce an active lignin substrate for binderless fiberboard production. The composition, morphology, and crystallinity index (CrI) analysis of fibers showed that the HCW treatment increased the CrI and lignin content of the treated fibers through partial removal of hemicelluloses. Simultaneously, the HCW treatment produced some granules and holes on the surface of the fibers, which possibly facilitated the accessibility of the laccase mediator. Milled wood lignins and enzymatic hydrolysis lignins isolated from the control and treated fibers were comparatively characterized. A reduction of molecular weight was observed, which indicated that a preferential degradation of lignin occurred after exposure to the laccase mediator. Quantitative (13)C, 2D-HSQC and (31)P NMR characterization revealed that the integrated treatment resulted in the cleavage of β-O-4' linkages, removal of G' (oxidized α-ketone) substructures, and an increase in the S/G ratio and free phenolic hydroxyls.

To achieve high value-added utilization of lignin extracted from the biorefinery process in the wood composite industry, binderless particle boards were manufactured by bamboo materials combined with alkaline lignin (AL) in various proportions under various hot-pressing conditions. To elucidate the reactivity and chemical transformations of lignin macromolecules during the hot-pressing process, lignin samples were isolated from the corresponding boards and characterized by highperformance anion-exchange chromatography (HPAEC), gel permeation chromatography (GPC), quantitative 31 P-NMR, and 2D-HSQC NMR. The best bonding strength (1.36 MPa) of the binderless particle boards was obtained under the conditions of 180 °C, pressure 5 MPa, and lignin/bamboo mass ratio 0.4. The molecular weight of the lignin samples decreased from 3260 to 1420 g/mol during hot-pressing. The NMR results showed that the contents of β-O-4' and β-β' linkages were reduced and β-5' linkages were increased as the hot-pressing temperature rose. Simultaneously, the percentage of G-type and H-type lignins as well as the content of phenolic OH increased.

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