Transparent wood has been gaining traction recently as an advanced functional material that could replace glass and plastic in consumer applications. According to a recent life cycle assessment study, transparent wood may offer a more environmentally friendly alternative to traditional optical materials.
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Introducing Transparent Wood
German scientist Siegried Fink first fabricated transparent wood in 1992, and his method has been improved on by subsequent research. Transparent wood is produced when you replace wood’s lignin content with transparent plastic materials. Lignin is the biopolymer in wood that supports plant tissue.
Transparent wood has come under scrutiny in recent years because it exhibits a number of interesting physical, mechanical, and optical properties.
It is as strong as normal timber but weighs less. It is also relatively straightforward to imbue wood with desired properties by adding various agents to the plastic material, replacing lignin.
Typically, fast-growing, low-density balsa wood is used as the primary material. This is treated in a room-temperature oxidizing bath, which bleaches it and removes opacity. Then, a synthetic polymer (usually polyvinyl alcohol or PVA) is injected to create a transparent material.
The wood’s natural cellulose combined with the polymer filler make it more durable for less weight than glass, capable of withstanding much stronger impact force than glass without breaking, and unlike glass which shatters if it simply bends or splinters under too much force.
Environmental Advantages
Like other plant-derived materials, transparent wood has numerous environmental advantages. Notably, it can be grown (rather than extracted) indefinitely, with new growth also capturing and sequestering carbon dioxide from the atmosphere. As wood, it is also biodegradable.
Recently, biochemical engineers from the Indian Institute of Technology published the results of a life cycle assessment of transparent wood. Their article, published in the journal Science of the Total Environment, stated that the renewable and biodegradable features of transparent wood make it more environmentally friendly than transparent plastic used for similar applications.
Currently, petroleum-based plastics like polypropylene, polyvinyl chloride (PVC), acrylic, polyethylene, and others supply relatively huge sections of the global industry’s need for new materials. These materials lead to environmental damage at multiple stages in their life cycle, from raw material (oil) extraction through to treatment, manufacturing, and disposal.
These materials often act as a substitute for glass because they can be made transparent. They are used in applications where the natural fragility of glass makes it inappropriate or unsafe, such as in safety screens or electronic interfaces.
Transparent wood made with sodium chlorite as the lignin-removing agent had a much smaller environmental impact than transparent wood using methacrylate polymer, according to the life cycle assessment.
In terms of end-of-life concerns, the study found that glass is actually more environmentally friendly than transparent wood, as it is easier to recycle and non-toxic if it does find its way into landfills (eventually breaking down into silica sand). But in this respect, transparent wood still outperformed plastic alternatives.
Applications
Transparent wood was first developed to help teach students about wood’s anatomy. It is still used for this application today, making wood’s internal structure visible. In research, transparent wood methods have been used to make 3D and deep imaging models of plant and animal tissues.
Transparent wood is also much more thermally efficient than glass, which could significantly reduce energy costs when applied as windows in construction settings. Currently, about a quarter of the energy used to heat buildings is lost through inefficient glass windows in low temperatures. Enhancing the energy efficiency of buildings through new window materials could have significant impacts on our total carbon costs.
As a glass replacement, transparent wood would give architects much more design freedom, as they would be able to incorporate natural light into buildings with load-bearing and structural transparent panels.
Transparent wood is also expected to find applications in the automotive sector, where companies are already investing in research and development.
For example, engineers are working on integrating electronics into touch-sensitive transparent wood. This would make wooden panel tactile dashboards in the cars of the future, offering unique aesthetic and safety advantages.
Cutting-edge applications for transparent wood are also under development. For example, quantum dots can be embedded into transparent wood to create wood-based light-emitting diodes (LEDs). This would create a naturally diffuse source of light that could be incorporated into building panels such as walls and ceilings.
Transparent wood could also provide shielding against electromagnetic interference (EMI) through the addition of magnetic nanoparticles. This could be used to shield security-critical electronic infrastructures such as servers and telecommunications.
Limitations
There still exist some barriers to transparent wood’s widespread adoption. The largest among these is that no method has yet been developed for scaled-up fabrication. For example, polymers tend to shrink during polymerization, which results in defective transparent wood products.
We currently do not understand the interactions between light and wood well enough to accurately predict how transparent wood will react over time under various lighting conditions. For example, different species of wood have different refractive indices, which result in different optical properties in transparent wood.
To overcome challenges like these, more research is needed in wood nanotechnology to fully understand the age-old material’s cutting-edge properties.
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References and Further Reading
Androff., A. (2021). Transparent Wood Could Be the Window of the Future. [Online] USDA. Available at: https://www.usda.gov/media/blog/2020/10/01/transparent-wood-could-be-window-future
Harikrishnan, K.S., (2022). Transparent wood could soon replace plastics. [Online] Phys.org. Available at: https://phys.org/news/2022-10-transparent-wood-plastics.html
Li, Y., et al (2018). Optically Transparent Wood: Recent Progress, Opportunities, and Challenges. Advanced Optical Materials. doi.org/10.1002/adom.201800059.
Mi, R., et al (2019). A Clear, Strong, and Thermally Insulated Transparent Wood for Energy Efficient Windows. Advanced Functional Materials. doi.org/10.1002/adfm.201907511.
Rai, R., R. Ranjan, and P. Dhar (2022). Life cycle assessment of transparent wood production using emerging technologies and strategic scale-up framework. Science of the Total Environment. doi.org/10.1016/j.scitotenv.2022.157301.
Transparent Wood. [Online] The Constructor. Available at: https://theconstructor.org/building/transparent-wood/29163/
Wild, S. (2019). Transparent wood: the building material of the future? [Online] Horizon. Available at: https://ec.europa.eu/research-and-innovation/en/horizon-magazine/transparent-wood-building-material-future
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