Transparent Wood Composites Fabricated by Impregnation of Epoxy Resin and W‑Doped VO2 Nanoparticles for Application in Energy-Saving Windows

Two types of transparent wood composites with anisotropic structure for energy-saving windows were successfully fabricated by infiltration of epoxy resin dispersion containing tungsten-doped vanadium dioxide nanoparticles (W-doped VO2 NPs) into the delignified wood template and subsequent polymerization. The well integration of the epoxy resin, W-doped VO2 NPs, and the pore-structured wood endowed the anisotropic composites with high visible transmittance (68.2% for the composite prepared from longitudinally cut trees (L-composite), 73.3% for the composite prepared from radically cut trees (R-composite)), obviously different mechanical performance (fracture stress of 74.57 MPa (L-composite) and 56.14 MPa (R-composite) and modulus of 1.47 GPa (L-composite) and 1.23 GPa (R-composite)), and low thermal conductivity (0.20 W·m–1 K–1 (L-composite) and 0.32 W·m–1 K–1 (R-composite)). Moreover, these two kinds of W/VO2 transparent wood composites both show an outstanding thermoregulation ability when they are used as windows. A significant amount of heat (from a simulated light source) was reflected by VO2 NPs, and as a result, the indoor temperature of a demo system had a significant slower temperature increase rate when compared with that for a similar system with a common glass panel applied. Novel transparent wood composites combining a low thermal conductivity wood template and thermochromic VO2 NPs provide a potential solution for replacement of heavy, high thermal conductivity, and infrared transparent glass but still meet indoor occupancy view perception.