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To comprehend the biosynthesis processes of conifers, it is essential to investigate the disparity between the cell wall shape and the interior chemical structures of polymers throughout the development of Chinese pine. In this study, branches of mature Chinese pine were separated according to their growth time (2, 4, 6, 8 and 10 years). The variation of cell wall morphology and lignin distribution was comprehensively monitored by scanning electron microscopy (SEM) and confocal Raman microscopy (CRM), respectively. Moreover, the chemical structures of lignin and alkali-extracted hemicelluloses were extensively characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The thickness of latewood cell walls increased steadily from 1.29 μm to 3.38 μm, and the structure of the cell wall components became more complicated as the growth time increased. Based on the structural analysis, it was found that the content of β- O -4 (39.88–45.44/100 Ar), β-β (3.20–10.02/100 Ar) and β-5 (8.09–15.35/100 Ar) linkages as well as the degree of polymerization of lignin increased with the growth time. The complication propensity increased significantly over 6 years before slowing to a trickle over 8 and 10 years. Furthermore, alkali-extracted hemicelluloses of Chinese pine mainly consist of galactoglucomannans and arabinoglucuronxylan, in which the relative content of galactoglucomannans increased with the growth of the pine, especially from 6 to 10 years. • The Chinese pine branches were systematically revealed. • The thickness of cell wall was enhanced gradually in late wood. • The lignin macromolecule polymerized gradually with Chinese pine growth. • The alkali-extracted hemicelluloses mainly consist of galactoglucomannans and arabinoglucuronxylan. [ABSTRACT FROM AUTHOR]

Elucidating the structural variations of lignin during the pretreatment is very important for lignin valorization. Herein, poplar wood was pretreated with an integrated process, which was composed of AlCl 3 -catalyzed hydrothermal pretreatment (HTP, 130–150 °C, 1.0 h) and mild deep-eutectic solvents (DES, 100 °C, 10 min) delignification for recycling lignin fractions. Confocal Raman Microscopy (CRM) was developed to visually monitor the delignification process during the HTP-DES pretreatment. NMR characterizations (2D-HSQC and 31P NMR) and elemental analysis demonstrated that the lignin fractions had undergone the following structural changes, such as dehydration, depolymerization, condensation. Molecular weights (GPC), microstructure (SEM and TEM), and antioxidant activity (DPPH analysis) of the lignins revealed that the DES delignification resulted in homogeneous lignin fragments (1.32 < PDI < 1.58) and facilitated the rapid assemblage of lignin nanoparticles (LNPs) with controllable nanoscale sizes (30–210 nm) and excellent antioxidant activity. These findings will enhance the understanding of structural transformations of the lignin during the integrated process and maximize the lignin valorization in a current biorefinery process. [Display omitted] • The microcosmic distribution and changes of lignin were visualized investigated. • Structural changes of lignin during the integrated HTP-DES process were illustrated. • Synergistic HTP-DES method was developed for fractionation of lignin. • High yields of tailored lignin nanoparticles were obtained. • Possible chemical variations of lignin during the synergistic HTP-DES were investigated. [ABSTRACT FROM AUTHOR]