Natural wood has been a key resource for construction, fuel, and furniture, valued for its versatility, renewability, and aesthetic charm. Yet, novel possibilities for wood are emerging as scientists devise methods to fine-tune the material’s optical, thermal, mechanical, and ionic transport characteristics through chemical and physical alterations to its inherently porous structure and chemical composition.
In pursuit of this objective, researchers have devised innovative strategies for modifying wood in recent years, imbuing it with new capabilities.
These advancements open the door to potentially substituting conventional, non-renewable, petroleum-based materials in diverse applications, including automobiles, energy storage, construction, and environmental remediation. This shift signifies a departure from the traditional domains of construction and paper industries for wood.
Transparent wood is poised to become versatile, with potential applications ranging from ultra-durable smartphone screens to soft, luminous light fixtures. Additionally, it could be utilized in structural elements, such as windows capable of changing colors.
Advancing research
Siegfried Fink created transparent wood by removing the pigments from plant cells, a process he detailed in a specialized journal focused on wood technology.
For over ten years, Fink’s 1992 publication stood as the definitive source on see-through wood until another scientist at KTH Royal Institute of Technology in Sweden, Lars Berglund, came across it, according to Ars Technica.
Concurrently, another group of researchers, headed by materials scientist Liangbing Hu at the University of Maryland in College Park, has been actively involved in advancing transparent wood through direct engineering of natural wood.
Wood consists of numerous small vertical channels, resembling a tightly bound bundle of straws held together with glue. These tubular cells serve to transport water and nutrients within a tree. When the tree is harvested and moisture evaporates, air pockets are left behind.
According to Ars Technica, to produce transparent wood, scientists must initially alter or eliminate the glue, known as lignin, which binds the cell bundles together and imparts the earthy brown color to trunks and branches. After bleaching or removing lignin’s color, a milky-white framework of hollow cells remains.
The resulting framework remains non-transparent because the cell walls refract light differently than the air in the cell pockets, a characteristic known as the refractive index. Achieving transparency involves filling these air pockets with a material such as epoxy resin, which bends light to a similar degree as the cell walls, rendering the wood see-through.
Varied properties
The research teams created see-through wood, an energy-efficient, light-collecting building material. They follow two main steps to make it: removing lignin, which absorbs light, and filling the wood with a polymer-like epoxy that matches the refractive index.
This transparent wood has about 80 percent optical haze (a measure of scattered light), allowing more than 85 percent of light to pass through. It can let in sunlight without causing glare, leading to energy savings and comfortable indoor lighting. Transparent wood’s high haze ensures even indoor lighting.
It also boasts strong mechanical integrity (around 100 MPa), absorbs impact energy effectively, and is ductile, addressing safety concerns typically associated with glass materials.
Furthermore, transparent wood surpasses glass as an insulator, potentially aiding buildings in retaining or repelling heat. In their work, Hu and his team utilized polyvinyl alcohol (PVA), a polymer commonly found in glue and food packaging, to infuse wood skeletons. This resulted in transparent wood with a heat conduction rate five times lower than that of glass.
Berglund and the team at KTH and Georgia Institute of Technology also discovered a way to replicate the functionality of smart windows, capable of transitioning between transparency and tinted states to control visibility or block sunlight. Their method involved layering an electrochromic polymer—capable of changing color through electricity—between transparent wood layers coated with an electrode polymer for conducting electricity, according to ARS Technica.
Scientists now aim to enhance the eco-friendliness of transparent wood by minimizing the use of harmful chemicals and fossil-based polymers in its production.
Source: IE
