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Author contributions All authors contributed to the review article. The literature study and the first draft of the article were written by Thabisile Jele, and all authors reviewed, revised, and made relevant contributions and suggestions for the submitted manuscript. All authors read and approved the final manuscript. Funding Open access funding provided by University of KwaZulu-Natal. Authors wish to acknowledge fund- ing received from the South African Technology Innovation Agency (TIA) under the South African Forestry Bio-economy Innovation Cluster (FBIC), Programme 2 and the CSIR Parlia- mentary Grant funding 2022/2023. Declarations Competing interests The authors declare no competing inter- ests. Consent for publication All authors consent to the publica- tion of this review. Open Access This article is licensed under a Creative Com- mons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Crea- tive Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. References Al-Qahtani S, Aljuhani E, Felaly R, Alkhamis K, Alkabli J, Munshi A, El-Metwaly N (2021) Development of photo- luminescent translucent wood toward photochromic smart window applications. Indl Eng Chemy Res 60:8340–8350. https://doi.org/10.1021/acs.iecr.1c01603 Bi Z, Li T, Su H, Ni Y, Yan L (2018) Transparent wood film incorporating carbon dots as encapsulating material for white light-emitting diodes. ACS Sustain Chem Eng 6:9314–9323. https://doi.org/10.1021/acssuschemeng. 8b01618.s001 Bisht P, Pandey KK, Barshilia HC (2021) Photostable transpar- ent wood composite functionalized with an UV-absorber. Polym Degrad Stab 189:109600. https://doi.org/10.1016/j. polymdegradstab.2021.109600 Chen H, Baitenov A, Li Y, Vasileva E, Popov S, Sychugov I, Yan M, Berglund L (2019) Thickness dependence of opti- cal transmittance of transparent wood: chemical modifica- tion effects. ACS Appl Mater Interfaces 11:35451–35457. https://doi.org/10.1021/acsami.9b11816
The studies in this review revealed that wood of high density is desirable in the production of ETW because of its strength, even after delignification. Also, the ETW produced had high tensile strength. However, the disadvantages of high-density wood were long delignification time and low optical trans- mittance of ETW produced. A higher volume fraction of cellulose in wood resulted in high mechanical strength and low optical transmittance. The cellulose volume fraction was a tunable property which could be increased by the compression of delignified wood template. Longitudinal ETW had higher mechanical strength than radial ETW. On the contrary, radial delignified wood had greater mechanical properties than delignified longitudinal wood. Radial ETW had higher optical transmittance than longitudinal ETW. The conclusion. Radial ETW and axial ETW had thermal conduc- tivities of 0.24 W m −1 K −1 and 0.41 W m −1 K −1 . It was concluded that restrained heat transfer in the radial direction results in greater light scattering than in the axial direction. In the case of delignification, the optical trans- mittance of delignified wood samples increased with increase in the degree of delignification how- ever mechanical properties of the ETW were nega- tively affected by increased levels of delignification. The tensile strength decreased with a decrease in lignin content in ETW samples. ETW produced by infiltration of PMMA had the highest mechanical properties. It can be concluded that the strength of the polymer positively contrib- utes to the strength of ETW produced. However, the low optical properties had to be improved by acety- lation. The applications of ETW include solar cells, windows, decorative materials, and screens. The main disadvantages of ETW are the limited scal- ability. Only ETW with a thickness less than 1 cm thick was successfully produced with acceptable optical properties (transmittance = 60%) (Li et al. 2018c). Although the short-term durability of ETW was proven, long term durability, especially in out- door applications, requires further research. Acknowledgments The authors acknowledge the Council for Scientific and Industrial Research, Biorefinery Industry Devel- opment Facility, South Africa for supporting this work.
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