Transparent Wood

Translucent Wood Could Give Architects A New Design Element

A lab in Stockholm, Sweden, is using nanotechnology to reimagine lighting with a wood composite that’s translucent, load-bearing and an advance in energy efficiency

The first thing you notice about the wood produced in Professor Lars Berglund’s lab is that it’s translucent. Forget oak, maple or cherry—this looks like a sheet of plastic.  

Berglund has manipulated it for just that effect, by stripping the wood of lignin and replacing it with an optically compatible polymer to create a composite that has the potential to transform indoor lighting into something that mimics natural light. Moreover, the material can contribute to load-bearing, reduce heating and cooling costs, and boost a building’s energy efficiency.  

It’s amazing what nanotechnology can do for architecture, engineering and construction nowadays.  

Eco-friendly materials engineering 

Berglund’s interest in polymers and plastics was sparked by an “inspiring” undergraduate class that set him on a career course that began with work on carbon fiber composites for aerospace. After teaching that topic for more than a decade, he joined Sweden’s Royal Institute of Technology and shifted his attention to wood composites. Today, Berglund also leads the European Commission-funded WoodNano Tech project, which launched in 2017 and is financed through 2022.  

What makes wood a good choice as a template for nanotechnology? 

“If you think about how concrete is made, or all the plastic materials that are dominating the market, we have to use a lot of energy to even create the materials,” Berglund said. “But in this case, the biological organism is doing the work for us. Not only has it taken zero energy to create the material, it also is storing carbon dioxide from the air in the tissue of the tree. This is a wonderful starting point. We have this incredibly functional material for building and at the same time from renewable resources. Not only that, it also has a low value of embodied energy.” 

While there is “big hype around nanotechnology today,” Berglund added, most of its applications relate to electronics or photonics. Typically, researchers engage in “bottom-up synthesis” that starts from atoms and then customizes the material they’re creating. And for those applications, a large structure would be something the size of a stamp.  

But Berglund and his team are working with a material that is already nanostructured and porous, “which means we can use this as a substrate for further functionalization,” he said. The composite can be infiltrated with additional functional materials, and this can be done on a large scale.  

“We could potentially, in the future, have these huge structures which are still based on nanotechnology, and they can be processed partly by these established industrial methods,” Berglund says.  

A lightbulb moment 

Traditionally, illumination involved using a light source and diffuser that scatters and softens the light. But the degree of brightness varies across the room. Wood’s internal structure fosters a certain amount of natural scattering that the research team has found a way to harness and exploit. The result is a room that’s more uniformly and comfortably lit, with no areas where the light is too harsh or too dim.  

Berglund’s work in this area focuses on integrating quantum dots into that natural wood infrastructure. The dots are semiconductor atoms that fluoresce when exposed to UV light. Berglund used an analogy that helps to explain the concept in layman’s terms: Samsung televisions use quantum dots to produce a brighter light. Because Berglund and his team are embedding LEDs into their wood composite, an entire wall or ceiling can become a source of evenly distributed—and more energy-efficient—light. 

“We have this wood substrate. We have removed the lignin. We introduce a polymer and then these quantum dots are distributed in this polymer illiquid,” Berglund said. “So, they become part of the whole composite structure as well.” 

Structured for further functionality 

The LED-embedded composite also supports load-bearing. “Since we have this wood skeleton, our light source can also carry load,” Berglund said. “We could integrate this in the ceiling; it would be part of the load-bearing structure.” 

Additionally, Berglund and his team have been experimenting with integrating materials other than polymers: using phase change material that can convert the wood composite into an energy storing device. That capability has been of particular interest to architects. 

Berglund explains:  

“Let’s say we have a translucent panel in the house. We have particles inside our wood material: the polymer, the wood substrate and these particles of phase change material. When the sun shines through the transparent translucent wood, it heats up. We are melting these particles, which means that some of the energy that should have gone into the house is consumed in melting these phase change material particles.” 

“So, the first advantage is that the room doesn’t get as hot as it would have gotten otherwise. Then, when the sun goes down, the molten particles of phase change material start to crystallize again, and then they give off heat. We are conserving some of the solar energy and we’re using it in the evening when it starts to cool down.” 

All this functionality comes from what, to the naked eye, appears to be an utterly unremarkable piece of translucent plastic. That appearance has also been subject to the team’s attention given the importance of aesthetics in architecture. As a reminder that the base material is wood, the composite has been given a surface texture like that of wood. 

Windows open to more smart innovation 

Berglund and his team are also experimenting with electrochromic smart windows. These, too, make use of polymers that are applied as a thin coating. Through use of a switch, they can control the amount of outside light that enters a room and even the color of that light.  

The advantage over curtains or shades is that the outside glare can be controlled without blocking the view, and the dimming or brightening can unfold gradually. It’s “a more elegant way” of regulating the light levels, Berglund said.  

The work to date has been recognized with “a couple of patents, and there is one company working on developing this basic patent,” Berglund said. He said he is not at liberty to name the company, and he estimates that the first products are still a few years from hitting the market. 

Still, commercialization is not Berglund’s chief concern. Rather, his primary motivation is “curiosity-driven research.” And that’s clearly working well for him.  

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