Transparent Wood Materials

Due to the distinctive structures that result from its natural growth, wood is a commonly utilized structural material with exceptional mechanical qualities. Different woods exhibit an incredible range of mesostructures depending on their kinds and geographic variances. In recent years, interest in transparent wood (TW), a biocomposite material with optical transparency in the visible range, has increased due to its enormous potential for environmentally beneficial applications, such as in the building sector and functionalized organic materials. The aim of this chapter is to describe the latest progress in the field of material properties (mechanical, optical, electromagnetic) of transparent wood.

Consumer devices of today are created from hazardous and non-renewable materials. Additionally, they are rigid, heavy, and produced in an energy-inefficient manner using CO₂-producing processes. Also, synthetic textile fibres have always had strong application possibilities in the textile industry due to favourable physical characteristics. Although petroleum-based polymers, including polyethylene terephthalate and polyethylene naphtholate, can address the stiffness issue, they have a large carbon footprint and generate toxic waste. Scalable, flexible, and environmentally friendly techniques in electronics production could provide solutions to the problems in the field. Electronics should ideally incorporate such substrates without degrading the device's performance. Wood has been extensively employed in the domains of construction, flooring, and furniture as one of the most sustainable materials. The development of transparent wood broadens wood’s uses, including light, thermal, electromagnetic, and energy management fields. Nevertheless, the majority of the reported transparent woods are made by impregnating polymers like polymethyl methacrylate, epoxy resin, or polyvinylpyrrolidone. Despite major advancements in functional transparent wood, programmable, light, stretchable, and thin transparent wood with shape memory has only recently been created during the last few years. This chapter explains the most current developments in materials that are ideal for creating smart transparent wood and have outstanding stimuli-responsive, shape memory, reprocessing, and self-healing capabilities.

Due to its high optical transparency, excellent thermal insulation, and great durability, transparent wood is a desirable structural material for energy-efficient buildings, electronics, packaging, and nanotechnologies. The transparent wood enhances the aesthetic and practical qualities of wood. A lot of work has gone into making transparent wood with luminous, electrochromic, thermochromic, and photo-switchable functionalities by incorporating quantum dots, nanoparticles, or dyes. Because of their superior mechanical qualities and immense potential to function as renewable and CO₂-storing cellulose scaffolds for cutting-edge hybrid materials with embedded functionality, wood-derived cellulose materials obtained by structure-retaining delignification are gaining increasing attention. A wide range of characteristics is produced by applying various delignification protocols and numerous additional processes, such as polymer impregnation and densification. Due to the scarcity of bio-based monomers that combine advantageous processing with high performance, the sustainable development of biocomposites has been constrained. Nonetheless, because of its renewable and biodegradable qualities, transparent wood has the potential to replace traditional petroleum-based polymers because of the growing knowledge obtained during the last few years which is presented in the following chapter.

The emergence of the concept of transparent wood has created a new frontier in wood modification, attracting academics to investigate it further and examine more functionality and production methods. In cutting-edge applications for architecture, new energy vehicles or spacecraft, it is very desirable to prepare a lightweight yet highly stable bio-based structural material that is sustainable and recyclable. In recent studies, transparent wood which has the potential to be widely used as new energy-saving material is mainly limited by its thickness which was either thin and highly anisotropic or thick and isotropic but weak. Therefore, new methods of its fabrication have been proposed to primarily increase the mechanical properties using multilayer lamination or densification.

The objective of this chapter is to acquaint the reader with information about recent progress made in the field of manufacturing biocomposite material—transparent bamboo. In the past few years, there has been a growing interest among researchers to develop a transparent material derived from fast-growing natural bamboo as a promising and sustainable alternative building material, smart house applications, electronic products, and aesthetically pleasing materials. Although bamboo has a significantly shorter growth cycle than wood, it is difficult to produce transparent items due to its high density and absence of lateral cell structures. Despite that, bamboo has many advantages over traditional wood but there are still many challenges which must be addressed before its practical applications.

Traditional energy production methods, such as burning fossil fuels, are harmful to the earth's environment, resulting in major, planet-scale issues, and climate change. As a result, renewable and green energy technologies have become increasingly popular in recent years. Improvements in solar panel efficiency, in particular, have piqued researchers’ interest, as the sun is a year-round available source of energy that may be used efficiently for energy generation. However, due to reflection at the air/glass interface, a considerable portion of the incident solar energy is lost. The increased need for flexible electronics and solar energy conversion devices has fuelled a pursuit of high-quality paper-based materials with good mechanical flexibility and optical qualities including high transparency and haze. High optical transmittance and haze, superior mechanical characteristics, a smooth surface, and low thermal conductivity characterize transparent paper and wood. This qualifies it as a solar cell assembly substrate with potential in energy-efficient construction applications. High optical transparency is required for solar cell substrates, but the high optical haze is preferred to maximize light dispersion and, as a result, absorption in the active components.

Wood is an available and sustainable substrate which has the potential for large-scale nanotechnology functionalization. Most materials used in optical lighting applications must create a homogeneous illumination and have high mechanical and hydrophobic requirements. But they are rarely environmentally beneficial. The large heat loss/gain through windows contributes to high energy consumption in buildings. Furthermore, the traditional glass fabrication method causes numerous environmental issues. Transparent wood-based composites are gaining importance in smart window applications. To save energy, a novel material called optically transparent wood is being developed for light-transmitting structures in buildings. This material combines optical and mechanical performance. Buildings that are eco-friendly and energy efficient are desirable from a sustainability standpoint, especially considering the current global energy and environmental crisis. Therefore, this chapter highlights the recent progress and applications of transparent wood in the field of smart windows.

To tackle energy and climate change challenges, renewable energy production and reduction of building energy consumption are required. To save energy, a novel material called optically transparent wood is being developed for light-transmitting structures in buildings. This material combines high optical transparency, outstanding mechanical characteristics, and superior thermal insulation. Due to its ability to regulate form, the transmitted light intensity distribution is adjustable. The resulting transparent wood also has excellent mechanical strength, good impact absorption, and excellent thermal insulation qualities. Transparent wood shows enormous promise as a cutting-edge practical and intelligent building material due to a combination of these properties. The following chapter summarizes the importance, recent progress, and possible applications of transparent wood in smart buildings.

Since transparent wood has the potential to become a suitable building material, its fire characteristics also become more important. During its preparation, several components are combined. One of them is wood modified by one of the many methods used, and others are synthetic (or natural) polymers. The scope devoted to this chapter is not able to cover all the specific materials due to the variety of combinations that can be prepared in this manner. The first part, therefore, contains a description of the individual components, their chemical composition, and their thermal decomposition. Frequently used components are processed as separate subsections. However, in some cases, groups of materials that include many substances are used to produce transparent wood. These are therefore combined into common units for the sake of greater clarity and fluidity of the text. The second part of this chapter is devoted to the fire properties of a specific type of transparent wood. It contains a description of its production as well as information regarding the cone calorimeter through which the samples were measured. It also contains the measurement results and, finally, the prediction of some other properties. The obtained data are evaluated in the form of graphs and compared with the results of other authors.