Conventionally, wood is used in making furniture, construction and as a source of fire. But now, researchers are exploring the possibility of making wood transparent as an eco-friendly alternative to glass.
Researchers are looking to tune wood’s optical, thermal, mechanical and ionic transport properties by chemically and physically modifying its naturally porous structure and chemical composition. “Such modifications can be used to produce sustainable, functional materials for various emerging applications such as automobiles, construction, energy storage and environmental remediation,” says a paper titled ‘Engineered Wood’, published in Annual Reviews.
Transparent wood is created when wood from the fast-growing, low-density balsa tree is treated to a room temperature, oxidising bath that bleaches it of nearly all visibility. It is then penetrated with a synthetic polymer called polyvinyl alcohol (PVA), creating a product that is virtually transparent, according to the US Department of Agriculture.
In 1992, German scientist Siegfried Fink developed the initial transparent wood, a creation that researchers have refined further. In simple words, it is made by removing the lignin (a polymer that’s found in the cell walls of plants) from wood and replacing it with clear plastic materials.
The advantages of using wood over plastic are numerous. Apart from being abundant and renewable, wood is also an eco-friendly alternative to high-carbon footprint materials.
Despite advancements, the widespread use of natural wood is constrained by its opaque appearance, modest mechanical strength compared with metals like aluminium and steel, and elevated thermal conductivity when compared to foams and wools, according to researchers.
Adopting transparent wood could also be cost-effective. It offers about five times better thermal efficiency than glass, reducing energy expenses.
For a green future
In recent research, scientists created transparent wood using acrylic derived from natural basswood and examined its resistance to various elements. The research paper “Comprehensive assessment of transparent wood degradation” was published in 2023 by Igor Wachter et al of University of Technology in Bratislava, Slovakia. The transparent wood showed strong resistance to fungi. In fire tests, it ignited later and produced less harmful carbon monoxide than regular wood. The material also experienced changes in colour and transmittance when exposed to UV radiation, with significant changes occurring in the first few hours.
The challenges identified by the researchers include ensuring durability against fire, microorganisms and weathering, along with the need to scale up production and reduce environmental impact. To overcome these challenges, efforts are directed towards exploring stability improvement methods, optimising production processes, and adopting environmentally friendly chemical approaches.
Now, is transparent wood market-ready?
Researchers say not yet. “Government incentives for engineered wood to displace petroleum-based polymers will accelerate market penetration.”
However, ‘transparent wood’ is not problem-free. A study at the University of Maryland highlighted three important challenges.
It says, the first challenge is creating high-performance materials with good product durability and service life. Currently, most modification methods have focused on enhancing the performance of wood. Little research has been conducted on the durability of wood-based materials when exposed to fire, microorganisms, water, or weathering. “This is a crucial factor to consider due to the hydrophilicity and biodegradability of the wood components.”
The second challenge is scaling up fabrication and reducing manufacturing and installation costs. One approach to tackle this is the use of high temperature and pressure to facilitate the diffusion of chemicals in the wood microchannels, resulting in a more homogeneous modification. The third challenge the paper mentions is that of reducing environmental pollution. Toward this goal, researchers are investigating the use of green solvents for wood de-lignification such as deep eutectic solvents or organic acid, which lead to much lower environmental impacts.