Cellulose (2023) 30:5447–5471
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Fig. 1 Applications of engineered transparent wood composites (Li et al. 2018b, 2018c; Wan et al. 2021; Chutturi et al. 2022)
good heat storage, large latent heat of melting and crystallisation (76 J g −1 and 74 J g −1 , respectively), tunable optical transparency during phase change, and thermal insulation properties. In cases where the ETW is used as a window or roof, a consistent/ uniform lighting and improved thermal insulation are guaranteed due to a combination of high opti- cal transmittance and haze (Montanari et al. 2019). Li et al. (2019b) assembled perovskite solar cells with good long-term stability on a transparent wood substrate at low temperature (< 150 ᕑ ). Even though studies have been conducted to produce ETW with excellent strength and optical properties, there is a need to improve its scalability by reducing polymer shrinkage due to polymerisation, eliminate polymer cell wall interface gaps by improving polymer infil- tration, improve the short and long-term integrity of ETW, especially in outdoor applications, exploit the natural characteristics of wood to the benefit of the EWT (e.g. aesthetic patterns), and alleviate the optical constraints of ETW related to thickness by surface modification, lamination and multilayer- ing (Jia et al. 2019; Mi et al. 2020a). Several stud- ies detailing ETW preparation methods, optical and mechanical performance, and thermal properties references arranged in ascending order of the publi- cation year are summarised in Table 1. This review article details the ETW production process and how the nature of wood (wood density, composition,
wood directions, wood type and infiltrated polymer) affect the morphological, functional, optical, ther- mal, photo degradation and mechanical properties of EWT.
Production of ETW Various techniques have been developed to produce ETW. These techniques mainly consist of two main steps: delignification or lignin modification and poly- mer infiltration. The schematic diagram of the pro- duction process of ETW is shown in Fig. 2. Several studies described the process of immersing a piece of wood (balsa, birch, pine etc.) in sodium chlorite in an acetate buffer solution at high temperature (80–95 ᕑ ) for 6 to 12 h (Li et al. 2017a; Yaddanapudi et al. 2017; Fu et al. 2018; Qin et al. 2018). The process resulted in white coloured wood after the removal of lignin and part of the hemicelluloses because of the light scattering at the interface between the cell wall and air (Gan et al. 2017a). However, this solu- tion-based method was long, produced a lot of liquid waste, and used large volumes of chemicals to ensure complete immersion and weakened wood. Deligni- fied wood was characterised by delamination, fragil- ity and instability (Li et al. 2017a). Wu et al. (2019a) performed an optimisation study of delignification time and optical properties in the production of ETW. Delignification was done using sodium chlorite in an
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