Emerging Materials – Transparent wood composite, a clear alternative to plastic?

Credit: WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, licensed under CC BY-NC-ND 4.0

Transparent wood composites are an innovative and aesthetic building material made from timber that often has better mechanical properties than natural wood and is more biodegradable than glass or plastic. This modern material has natural beauty, impressive multifunctionality and sustainable benefits; learn more about how see-through wood might change the built environment and whether it can be sustainable.

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The Plastic Problem

The spread of plastic materials into the natural environment is one of the largest issues facing ecologists today. According to the UNDP, the plastics industry is actually the fastest-growing source of industrial greenhouse gases in the world. Since the 1950s, over 10 billion tons of plastic waste have been generated. This figure is expected to rise to 25 Billion by 2050.

Sadly, the majority of this waste has been discarded and huge amounts disposed of unethically. As a result, vast amounts of plastic have infiltrated the environment, damaging biodiversity, tarnishing natural beauty, destabilising ecosystems and adversely affecting human health. Plastic particles are ingested and inhaled by all organisms causing an increased risk of cardiovascular disease, stroke, cancer and diabetes in humans. Nanoplastics can even enter our bodies through the skin membrane. Most plastics are petroleum based. This means the production and extraction process is extremely environmentally damaging. Plastic production, presence and disposal have a seemingly endless domino effect of consequences throughout the planet.

Concerningly, the construction industry is one of the largest producers of plastics in the world today. This problem urgently needs to be resolved and one of the most effective ways to do so is through alternative materials. Petroleum-based plastics are not unique in their properties and can be replaced with more sustainable alternatives. One of these alternatives is the newly developed transparent wood.

A Revived Discovery

This material was first created in 1992 by Siegfried Fink for a functional study of wood structure. At the time, Fink’s transparent wood creation went unnoticed in the public eye, but it has since been rediscovered and redeveloped with sustainable construction in mind. In 2016 a research group led by Lars Berglund at The KTH Royal Institute of Technology recreated the bleaching process first used by Fink to achieve this mostly transparent form of wood. Their work received widespread media attention due to the bizarre novelty of this wood’s appearance. Now perspectives are shifting to the sustainable potential of this composite. The European Commission went so far as to provide over 2 million euros in grant money to Berglund’s Wood Nanotech research.

Credit: KTH royal institute of technology

How is it Transparent?

Wood is opaque mostly due to a light-absorbing biopolymer called lignin. However, a delignification process can remove the lignin from wood, allowing for up to 90% light transmission. The process can be performed on softwoods, hardwoods and even non-wood biomass such as bamboo.

The delignification process can vary but generally involves drenching the wood in a heated (80-100℃) sodium solution for 3-12 hours and then immersing it in boiling hydrogen peroxide. This bathing treatment weakens the lignin bonds in the wood, making it easier to separate. Once the lignin is separated, the wood is white. To achieve the transparent effect, the wood has to be immersed in a heated polymer resin bath for 12 hours, leaving the resin to seep into the pores and replace the missing lignin in the wood’s cellular structure.

The Benefits of Delignification

Delignification results in several practical improvements to wood properties:

Improved insulative qualities: Lignin is a powerful thermal conductor. Its removal reduces the overall thermal conductivity of wood and creates nanopores in the material, further contributing to its insulative qualities. Delignified wood, known as nanowood, boasts lower thermal conductivity than conventional insulators like styrofoam.

Source: ShanghaiTech University and American Chemical Society

Improved strength and stiffness: Collapsing pores in delignified wood and resin pore infiltration increases the density of the wood. Delignified wood demonstrates increased strength and stiffness. Mechanical ability tests were conducted on delignified bamboo (‘super bamboo’) and compared to the performance of natural bamboo. The ‘super bamboo’ was almost twice as strong as its unprocessed counterpart.

Source: ShanghaiTech University and American Chemical Society

Clear aesthetic: whilst this benefit is not practical, it’s hard to deny the novel aestheticism of transparent wood. The transparency also opens up a wider range of creative interior design applications. The wood can be used as a substitute for windows or as a structural component allowing more natural light entry. Transparency levels are also variable and dependent on polymer infiltration. A translucent form of the material can be made, which could be used in the style of clouded or stained glass.

Potential Applications

This material is about as versatile as they come. Many multi-functional treatments can be performed on the material, from hydrophobic modification to conductive carbon nanotube coating. Combining this with Its high mechanical ability, natural abundance and aesthetic look means it could be viable for structural bodies, insulation, technologically innovative components, windows or even just art.

Smart windows

An adjustable transparency window is one of the most exciting creations with delignified wood composites. Laminating an electrochromic polymer onto the transparent wood can modulate the material’s transparency by adjusting a connected power supply. The light management of any interior could even be controlled through a dimmer switch.

Cooling surfaces

Near-complete delignification produces a cooling wood that is effective at solar reflection and radiative cooling. The material temperature will always remain significantly below ambient temperature. A study which tested ambient temperature differences with the composite wood temperatures noted that the wood could be up to 10℃ cooler. The composite would be an ideal material for roofing panels in hot climates.

Touch-sensitive panels

WOODOO a materials science company based in Paris is one of the first to start creating transparent wood prototype products. Their project, ‘Augmented wood’, is seeking to use integrated electronics to create tactile wooden panels that could serve as car dashboards. Timothee Boitouzet, founder and CEO of WOODOO, says augmented wood ‘is weather-proof, more fire resistant, three to five times stronger, and transparent.’

A Sustainable Alternative?

The lignin extracted from the wood doesn’t have to go to waste. Demonstrating the impressive circularity potential of transparent wood, reused lignin can be used in recycled cardboard, paper products and plastics.

Wood is a regenerative material; with carefully managed and responsible collection, this resource can be maintained in abundance well into the future.

Like its original form, this wood is biodegradable and significantly more so than plastic or glass, reducing its long-term environmental damage and facilitating eco-friendly disposal.

However, there is a major issue at this stage of development. A suitable and effective polymer for resin infiltration has not been perfected—currently, most versions of the composite use ecologically damaging petroleum-based synthetic polymers. The future of this material does not end here though. Renewably sourced polymers are being extensively researched and technological advancements will certainly resolve this issue in years to come. Some polymers are even being made from natural gases and even carbon dioxide. Infusing delignified wood with polymers like this could make the material more circular and even reduce its carbon footprint further.

Transparent wood composites are not set to change the world or replace plastic just yet, but the potential for this material is very impressive and more research and development is needed. Nonetheless, interest in this material is gaining and the transparent Wood market size is projected to register appreciable gains by 2032 according to Global Market Research. Be sure to keep an eye out for future updates; one day, you’ll see this material in your built environment.

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