Spatial organization and connectivity of wood rays in Pinus massoniana xylem based on high-resolution µCT-assisted network analysis.

MAIN CONCLUSION: Spatial organization and connectivity of wood rays in Pinus massoniana was comprehensively viewed and regarded as anatomical adaptions to ensure the properties of rays in xylem. Spatial organization and connectivity of wood rays are essential for understanding the wood hierarchical architecture, but the spatial information is ambiguous due to small cell size. Herein, 3D visualization of rays in Pinus massoniana was performed using high-resolution µCT. We found brick-shaped rays were 6.5% in volume fractions, nearly twice the area fractions estimated by 2D levels. Uniseriate rays became taller and wider during the transition from earlywood to latewood, which was mainly contributed from the height increment of ray tracheids and widened ray parenchyma cells. Furthermore, both volume and surface area of ray parenchyma cells were larger than ray tracheids, so ray parenchyma took a higher proportion in rays. Moreover, three different types of pits for connectivity were segmented and revealed. Pits in both axial tracheids and ray tracheids were bordered, but the pit volume and pit aperture of earlywood axial tracheids were almost tenfold and over fourfold larger than ray tracheids. Contrarily, cross-field pits between ray parenchyma and axial tracheids were window-like with the principal axis of 31.0 µm, but its pit volume was approximately one-third of axial tracheids. Additionally, spatial organization of rays and axial resin canal was analyzed by a curved surface reformation tool, providing the first evidence of rays close to epithelial cells inward through the resin canal. Epithelial cells had various morphologies and large variations in cell size. Our results give new insights into the organization of radial system of xylem, especially the connectivity of rays with adjacent cells.

The Distribution and Polymerization Mechanism of Polyfurfuryl Alcohol (PFA) with Lignin in Furfurylated Wood.

There is increasing interest in furfurylated wood, but the polymerization mechanism between its internal polyfurfuryl alcohol (PFA) and lignin is still uncertain. This paper investigated the distribution of PFA and the feasibility of the polymerization of PFA with lignin in furfurylated balsa wood. The wood first immersed in the furfuryl alcohol (FA) solution followed by in situ polymerization and the distribution of PFA was characterized by Raman, fluorescence microscopy, SEM, and CLSM. Then, the mill wood lignin (MWL) of balsa wood and lignin model molecules were catalytically polymerized with PFA, respectively, studying the mechanism of interaction between PFA and lignin. It was concluded that PFA was mainly deposited in cell corner with high lignin concentration, and additionally partly deposited in wood cell cavity due to high concentration of FA and partial delignification. TGA, FTIR, and NMR analysis showed that the cross-linked network structure generated by the substitution of MWL aromatic ring free position by PFA hydroxymethyl enhanced the thermal stability. New chemical shifts were established between PFA and C5/C6 of lignin model A and C2/C6 of model B, respectively. The above results illustrated that lignin-CH2-PFA linkage was created between PFA and lignin in the wood cell wall.

Synthesis of High-Water-Resistance Lignin-Phenol Resin Adhesive with Furfural as a Crosslinking Agent.

In this study, furfural was used as a crosslinking agent to enhance the water resistance of lignin-phenol-formaldehyde (LPF) resin. The effect of the furfural content on the physicochemical properties of the adhesives was explored, and the possible synthesis mechanism of the furfural-modified lignin-phenol-formaldehyde (LPFF) resin adhesives was investigated. Compared with the LPF adhesive, the LPFF adhesive with 15% furfural content and 50% lignin substituent exhibited outstanding properties in all considered aspects; it had a high wet shear strength (1.30 MPa), moderate solid content (54.51%), and low viscosity (128 mPa∙s), which were 38.0% higher, 3.6% higher, and 37.5% lower than those of the LPF adhesive. Analyses via nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy confirmed that the furfural content improved water resistance of the lignin-based adhesive; this improvement was due to the formation of new chemical bonds between furfural and lignin to construct a dense crosslinked network structure. In addition, the decrease in viscosity and the increase in solid content enabled the adhesive to better penetrate into the wood porous structure, showing stronger adhesion. Therefore, the LPFF adhesive has superior water resistance, high strength, and good thermal stability; thus, it has a great potential for industrial applications.