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FROM NATURAL WOOD TO A HIGH-PERFORMANCE STRUCTURAL MATERIAL

Synthetic structural materials with exceptional mechanical performance suffer from either large weight and adverse environmental impact (for example, steels and alloys) or complex manufacturing processes and thus high cost (for example, polymer-based and biomimetic composites). Natural wood is a low-cost and abundant material and has been used for millennia as a structural material for building and furniture construction. However, the mechanical performance of natural wood (its strength and toughness) is unsatisfactory for many advanced engineering structures and applications. Pre-treatment with steam, heat, ammonia or cold rolling followed by densification has led to the enhanced mechanical performance of natural wood. However, the existing methods result in incomplete densification and lack dimensional stability, particularly in response to humid environments, and wood treated in these ways can expand and weaken. Here we report a simple and effective strategy to transform bulk natural wood directly into a high-performance structural material with a more than tenfold increase in strength, toughness and ballistic resistance and with greater dimensional stability. Our two-step process involves the partial removal of lignin and hemicellulose from the natural wood via a boiling process in an aqueous mixture of NaOH and Na2SO3 followed by hot-pressing, leading to the total collapse of cell walls and the complete densification of the natural wood with highly aligned cellulose nanofibres. This strategy is shown to be universally effective for various species of wood. Our processed wood has a specific strength higher than that of most structural metals and alloys, making it a low-cost, high-performance, lightweight alternative.

Recent Papers:

  • Song, J.; Chen, C.; Zhu, S.; Zhu, M.; Dai, J.; Ray, U.; Li, Y.; Kuang, Y.; Li, Y.; Quyispe, N.; Yao, Y.; Gong, A.; Leiste, U.H.; Bruck, H.A.; Zhu, J.Y.; Vellore, A.; Martini, A.; Li, T.*; Hu, L.* A General Strategy for Processing Wood into Super Strong and Tough Structural Materials. Nature, 2018, 554, 224.

RADIATIVE COOLING STRUCTURAL MATERIALS

Reducing human reliance on energy-inefficient cooling methods such as air conditioning would have a large impact on the global energy landscape. By a process of complete delignification and densification of wood, we developed a structural material with a mechanical strength of 404.3 megapascals, more than eight times that of natural wood. The cellulose nanofibers in our engineered material backscatter solar radiation and emit strongly in mid-infrared wavelengths, resulting in continuous subambient cooling during both day and night. We model the potential impact of our cooling wood and find energy savings between 20 and 60%, which is most pronounced in hot and dry climates.

Recent Papers:

  • Li, T., Zhai, Y., He, S., Gan, W., Wei, Z., Heidarinejad, M., Dalgo, D., Mi, R., Zhao, X., Song, J. and Dai, J; Yin, X*; Hu, L.* 2019. A radiative cooling structural material. Science, 364(6442), pp.760-763.

INNOVATIVE WOOD FOR BUILDING EFFICIENCY WITH SUSTAINABILITY

Modified wood materials can be used for improved building efficiency with advanced light and thermal management capability. We have developed transparent wood with guided sunlight passage and improved thermal insulation, which could greatly improve the thermal management for buildings in the summer and winter toward energy saving.

Recent Papers:

  • Zhu, M.; Song, J.; Li, T.; Gong, A.; Wang, Y.; Dai, J.; Yao, Y.; Luo, W.; Henderson, D.; Hu, L.*  Highly Anisotropic, Highly Transparent Wood Composites. Adv. Mater. 2016, 28, 5181–5187.

  • Li, T.; Zhu, M.; Yang, Z.; Song, J.; Dai, J.; Yao, Y.; Luo, W.; Pastel, G.; Yang, B.; Hu, L.* Wood Composite as an Energy Efficient Building Material: Guided Sunlight Transmittance and Effective Thermal Insulation. Adv. Energy Mater. 2016, 1601122.

TRANSPARENT NANOPAPER FOR BIODEGRADABLE ELECTRONICS

Our group has developed different generations of transparent paper and applied them to various devices. The focus is to use pure wood cellulose fibers to fabricate mesoporous structures with tailored optical, mechanical, thermal and electrical properties. These optical substrates are extremely attractive for advanced optoelectronics, flexible displays (especially emerging OLED displays), solar cells and advanced windows.

Recent Papers:

  • Huang, J.; Zhu, H.; Chen, Y.; Preston, C.; Rohrbach, K.; Cumings, J.; Hu, L.* ACS Nano, 2013, 7, 2106.

  • Zhu, H.; Zhu, S.; Jia, Z.; Parvinian, S.; Li, Y.; Vaaland, O.; Hu, L.*; Li, T.* PNAS, 2015, 112, 8971;

NANOMEMBRANE FOR BIOLOGICAL SYSTEMS  

Ion transport is a common process in many biological activities and in energy storage devices. It is the key to better understanding ion transport behavior for the development of ionic devices for biomedical and energy applications. We developed an electron battery that can generate a current of ions instead of electrons, such that those ions can be used for potential applications in energy and biosystems.  

Recent Papers:

  • Wang, C.; Fu, K.K.; Dai, J.; Lacey, S.D.; Yao, Y.; Pastel, G.; Xu, L.; Zhang, J.; Hu, L.* Inverted Battery Design as Ion Generator for Interfacing with Biosystems. Nature Communications, 2017, 8, 15609.

SOLAR STEAM AND WATER TREATMENT

Both fresh water shortage and water pollution are the most pressing issues for our globe, endangering the life of human beings and other living creatures. Desalination and water purification are general practices for addressing these issues, but constantly call for materials and devices with low cost and high efficiency. In this research direction, we are exploring the potential of nature-derived materials for application in water treatment. Natural wood presents rich mesostructures such as vessels and tracheids for water and nutrient conveyance in living trees, and will be employed in our research for designing water treatment devices. As one application, highly efficient solar steam generation device will be designed by integrating the solar energy absorption, thermal insulation, and water transport performance in natural wood, which can be used for desalination to obtain fresh water. In addition, the rich mesostructures and abundant functional groups of wood will be explored for the design of a wood membrane with catalytic properties, which will be used for water pollutant degradation. Wood cells are naturally designed for water transport, and therefore, it is feasible to utilize these structures for water treatment.

Recent Papers:

  • Zhu, M.; Li, Y.; Chen, G.; Jiang, F.; Yang, Z.; Luo, X.; Wang, Y.; Lacey, S.D.; Dai, J.; Wang, C.; Jia, C.; Wan, J.; Yao, Y.; Gong, A.; Yang, B.; Yu Z.; Das, S.; Hu, L.* Tree-Inspired Design for High-Efficiency Water Extraction. Adv. Mater. 2017, 1704107.

  • Chen, F.; Gong, A.; Zhu, M.; Chen, G.; Lacey, S.D.; Jiang, F.; Li, Y.; Wang, Y.; Dai, J.; Yao, Y.; Song, J.; Liu, B.; Fu, K.; Das, S.; Hu, L.* Mesoporous, Three-Dimensional Wood Membrane Decorated with Nanoparticles for Highly Efficient Water Treatment. ACS Nano 2017, 11(4), 4275-4282.