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Na 2 SO 3 and H 2 O 2 delignification process followed by infiltration of Cs x WO 3 /MMA mixture. Although the optical transmittance of ETW decreased with increased concentration of Cs x WO 3 , whereas the heat shielding ability increased, an optimum dos- age of 0.03 wt% in the Cs x WO 3 /MMA mixed solu- tion resulted in 72% transmittance and strength of 59.8 MPa and modulus of 2.72 GPa. Comparison of mechanical properties showed that transpar- ent wood was much stronger (strength = 60.2 MPa, modulus = 2.67 GPa) than CsxWO 3 /ETW (strength = 59.8 MPa and modulus 2.72 GPa), PMMA (strength = 39.6 MPa, modulus = 1.83 GPa) and natural wood (strength = 55.1 MPa, modu- lus = 5.67 GPa). The simulation test showed that Cs x WO 3 /ETW can be used as energy efficient smart windows (Yu et al. 2017). Hu et al. (2022) produced ETW with a very low thermal conductivity of 0.157 W m −1 K −1 after coating with a ZnO film via sono- chemical deposition process. The low thermal con- ductive made the ZnO coated ETW ideal for glazing applications.
polymer shrinkage during polymerization in the pro- duction of thick ETW (Li et al. 2018a). The applica- tions of ETW are discussed in the following sections and a summary provided in Table 2.
Building materials
Incorporation of ETW instead of glass as a building material resulted in improved optical transmittance ( 85%), no glare effect, optical haze (> 95%), peculiar light guiding effect with large forward to back scat- tering ratio (scattering ratio of 9 for 0.5 cm thick ETW), good thermal insulation (i.e. thermal conduc- tivity ~ 0.32 W m −1 K −1 and~0.15 W m −1 K −1 in the cross plane), alleviated safety issues associated with glass, simple and fast fabrication and scalability (Li et al. 2016a). ETW preserves the original cellulose nanofibers of wood which contribute to anisotropic properties. Li et al. (2016a) demonstrated that when ETW is used as a roof top it maintains uniform light- ing and a constant temperature inside the building. It was concluded that the application of ETW in a build- ing created comfortable living conditions and reduces energy costs. Li et al. (2019c) used a real house simulation test to confirm the infrared-heat shield- ing ability and energy storage performance of ETW composed of VO 2 (M)@SiO 2 and thermochromic microcapsules particles. The ETW was proposed to be suitable for building, furniture, thermal insulation, energy conversion, energy storage, and conservation.
Applications
ETW can be tailor made to fit the specifications of applications. For instance, the thickness of ETW depends on the thickness of initial wood chosen. The mechanical and optical properties of ETW can be controlled by the optical (i.e. refractive index) and mechanical properties of the polymer infiltrated dur- ing fabrication. However, for large scale applications, the loss of optical transmittance of ETW of high thickness is a problem. Also, there is need to reduce
Aesthetics material
Functionalisation of ETW extends its applications to decorative materials. For instance, addition of
Table 2 A summary of Applications of ETW
Application
References
Magnetic ETW
Gan et al. (2017a), Gan et al. (2017b) Yaddanapudi et al. (2017), Li et al. (2019c)
Building components (rooftop and windows)
Smart windows
Samanta et al. (2021) Chen et al. (2020)
Flame retardant ETW Aesthetic material
Wang et al. (2019a), Mi et al. (2020a), Mi et al. (2020b), Hoglund et al. (2021)
Smartphone screen
Magrini et al. (2021) Zhu et al. (2016a)
Photovolaic
Photovoltaic cells
Li et al. (2019b)
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