Amazing materials: Transparent Wood

  • The simple process of replacing the organic polymer lignin with a special mix of epoxies removes the colouring from wood and adds a new level of strength.
  • While many may see transparent wood as something of a novelty material, the practical benefits are immense.
  • Practical uses include replacement windows, high-end sports equipment and integration into solar panels and solar cells to name but a few.

Transparent wood is a type of a composite material that has the potential to revolutionise the fields of construction and the manufacturing of various products. It combines the benefits of wood as a material and the achievement of making it opaque. For now, transparent wood remains under development but advancements in the science of materials suggest that it will be widely available very soon.

The story of transparent wood

Transparent wood was created back in 1992 when German researcher Siegfried Fink sought to reveal the specific cavities in wood for the purpose of writing a book on a functional study of wood structure. This work inspired engineers from the Swedish Royal Institute of Technology, who collaborated with a research group at the University of Maryland, to start exploring the possibilities of creating transparent wood for more widespread use. The publication of the first results, as well as samples of transparent wood blocks last year, sparked the interest of many architects and engineers around the globe. The road to the final stages of development for this novel material is coming to an end.

How to make transparent wood

The key concept is to remove the organic polymer called “lignin” from the wood, which is the substance responsible for the wood’s brownish colouring. To achieve this targeted chemical removal, while keeping the rest of the material intact, the scientists follow a procedure that is similar to chemical pulping. This involves immersing the wood piece in a solution of water, sodium hydroxide and sodium sulphite and boiling it for about two hours.

Once all lignin has been removed, the wood becomes transparent although it is also very fragile. This is because lignin is what gives wood its rigidity since this polymer is a primary element of the cell walls. To compensate for this loss, scientists re-immerse the block in a new solution that consists of a special mix of epoxies that fill the emptied microscopic channels of the wood. These strengthen the wood while maintaining its transparency and biodegradability. This process lasts for about an hour, with the pressure in the bath interchanging from positive to negative in order to make sure that all wood channels are completely filled with the epoxy.

Advantages and possible applications

The resulting wood composite is much stronger than natural wood and allows up to 90% of light to pass through it. The material has the practical utilisation potential to replace glass and plastic materials in a myriad of possible applications. Some of the most notable first application examples include:

  • Replace glass windows on buildings – allowing the use of fewer frame elements since the composite wood can withstand loads much better than glass does. In addition to this, composite wood is immensely better in terms of thermal insulation when compared to glass, so it will likely have a hugely positive effect on the energy efficiency of buildings in the future.
  • Solar panels and solar cells can be equipped with composite wood that has a high light transmittance, better durability against environmental damage such as hail and the capacity to implement “light trapping” properties that reflect light back to the cells. This will reduce the rate of escaping rays and increase the energy efficiency of the panels.
  • Since wood is very light compared to steel, but also very strong with the addition of the epoxies and polymers, transparent wood may also be utilised as a key structural element by itself. We have already seen the implementation of a model house with its ceiling and roof being made by transparent wood. This combines unprecedented thermal insulation and structural integrity.
  • High-end sports equipment such as archery bows, various sticks and clubs, tennis rackets, etc can all potentially benefit from the added strength of transparent wood with no additional weight.
  • Wood is already a popular choice of material for fuselages and wings for small aircraft. As transparent wood is so much stronger we will likely see many significant developments in this field.

Current drawbacks

The main problem at this time is that development funding for transparent wood is running low. As a consequence research teams are being forced to spend time convincing potential investors about the usability potential of the material. The fact it is also unclear how best to achieve mass production in a cost-efficient manner is not helping at this point in time. However, when balancing the benefits of transparent wood with production costs going forward there are still high hopes for the future.

 

About: Bill Toulas

Passionate engineer and new technologies advocate, writing about the ways they shape our world and amplify our very existence. Believes that engineering is the art of changing this world forever, everyday, little by little, and sometimes all at once.

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