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ANISOTROPIC NANOWOOD

Scalable thermal insulator

Sci. Adv. 4, eaar3724 (2018)

Thermal insulating materials are highly desirable for various practical applications. Among such materials, nanocellulose is attracting attention because of its abundance and eco-friendly properties. It is known that anisotropic nanocellulose composites can serve as good thermal insulators. However, their poor mechanical properties prevent their large-scale application. Li and colleagues now report a scalable, anisotropic, light, strong and super thermally insulating nanowood made of naturally aligned cellulose nanofibrils.

The authors fabricated the nanowood by heating and chemically treating natural wood and subsequently freeze drying it. The formed nanowood is mesoporous with porosity as high as 91%. It is composed of hierarchically aligned cellulose nanofibril aggregates with large surface-to-volume ratios and high aspect ratios. Even though the nanowood is light, its mechanical strength is much higher than existing thermal insulating materials, which can be attributed to the bonding between the cellulose fibrils. Moreover, the nanowood exhibits low emissivity, capable of reflecting 95% of the solar thermal energy. The anisotropic property of the nanowood leads to anisotropic heat flow. The axial thermal conductivity is two times the transverse thermal conductivity. Consequently, the thermal dissipation in the axial direction is faster than in the transverse direction, which further enhances the transverse thermal insulation. The authors find that when the top surface is heated by a solar simulator, the backside of the nanowood is 27 °C lower than that of a silicon aerogel.

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Correspondence to Wenjie Sun.

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Sun, W. Scalable thermal insulator. Nature Nanotech 13, 272 (2018). https://doi.org/10.1038/s41565-018-0127-x

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