X. Zhao, L. Hu
University of Maryland,
Keywords: wood, thermal insulation, radiative cooling, energy-efficient buildings
Summary:Developing sustainable, lightweight, and mechanically strong thermal management materials is key for improving occupant comfort and lowering the carbon footprints of buildings. Wood is a structural material that has been used in construction for thousands of years due to its excellent mechanical strength, natural abundance, and low cost. However, natural wood features a relatively high thermal conductivity of 0.1–0.4 W/(m·K), which prevents it from effectively retarding heat loss. Additionally, natural wood is brown in color and absorbs ~ 50% of solar irradiation, which is insufficient to effectively block solar heat during hot weather. Herein, we engineer wood via complete delignification to render a porous structure with ultralow thermal conductivity of ~ 0.03 W/(m·K). Since the natural structure of the hierarchically aligned cellulose fibers was kept intact, the developed porous wood structure demonstrates high mechanical robustness that exceeds other commercial thermal insulation materials, such as Styrofoam and glass wools. We also demonstrate that densifying the porous wood structure via mechanical pressing enables continuous sub-ambient cooling during both day and night, significantly reducing the cooling loads required in hot weather . These newly engineered woods as a super thermal insulator and passive cooler show promising potential towards thermal comfort and energy-efficient buildings. References  T. Li, J. Song, X. Zhao, Z. Yang, G. Pastel, S. Xu, C. Jia, J. Dai, C. Chen, A. Gong, Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose, Science advances, 4 (2018) eaar3724.  T. Li, Y. Zhai, S. He, W. Gan, Z. Wei, M. Heidarinejad, D. Dalgo, R. Mi, X. Zhao, J. Song, A radiative cooling structural material, Science, 364 (2019) 760-763.