Researchers have developed a scalable, biodegradable, transparent bamboo material enhanced with a tungsten-doped vanadium dioxide (W-VO2) coating for energy-efficient windows. The composite achieves high transparency, solar modulation, and thermal insulation - outperforming traditional glass in hot climates.
Study: Sustainable Transparent Bamboo/W-VO2 Composites for Solar Modulation and Energy-Efficient Buildings. Image Credit: frantic00/Shutterstock.com
The full study was recently published in the Journal of Bioresources and Bioproducts and reported on the development and how it could be applied to energy-efficient buildings and solar modulation.
The Importance of Energy-Efficient Materials
Creating energy-efficient buildings starts with choosing the right materials, those that not only provide structural strength but also enhance thermal and optical performance to help reduce energy consumption and greenhouse gas emissions.
Today, buildings account for roughly 40 % of global energy use. A significant portion of that number (over 10% of annual electricity), goes toward heating, ventilation, and air-conditioning (HVAC) systems, and that number is only expected to grow.
One of the major culprits of energy inefficiency is the conventional single-pane glass window. With high thermal conductivity, it allows heat to transfer freely between the inside and outside of buildings, undermining efforts to maintain indoor temperature. It also comes with added drawbacks like glare from sunlight and breakability, raising both comfort and safety concerns. This stresses the need for innovative window materials that provide improved insulation, durability, and optical clarity - without compromising sustainability.
Cellulose, a renewable and abundant biopolymer, offers natural transparency thanks to its tightly packed molecular structure. But manufacturing transparent cellulose-based materials is often energy- and time-intensive.
A more practical alternative is transparent wood, which retains the natural wood framework, removes lignin, and fills the gaps with clear polymers. This results in high light transmittance and thermal insulation. While promising, transparent wood still faces hurdles - mainly around the use of petroleum-based resins, limited biodegradability, and challenges with scalability and mechanical consistency - that limit its immediate application.
The Potential of Bamboo
This is where bamboo enters the conversation.
As a fast-growing grass with highly aligned cellulose nanofibrils, bamboo offers excellent strength and toughness. It's composed of approximately 45 % cellulose, 25 % lignin, and 22 % hemicellulose, with its yellow tone stemming from lignin. Even when most lignin is removed, bamboo doesn’t become transparent due to persistent light scattering, mainly because of mismatched refractive indices.
To overcome this, polymers with optical properties that match the structure are often introduced. However, those solutions typically involve epoxy resins, which can compromise biodegradability. This presents a key challenge: how to develop transparent, high-performance bamboo that’s also fast, eco-friendly, and cost-effective to produce.
The Study That Offers a New Approach
In response, researchers have developed a simple and effective method to create transparent, biodegradable bamboo, eliminating the need for external polymers. The process centers on pressing delignified bamboo boards to align cellulose nanofibrils into a dense, ordered structure. By selectively removing lignin while preserving most of the hemicellulose, they improved the material’s structural stability throughout processing.
This directional pressing technique helps maintain nanofibril alignment, allowing hydrogen bonds to form a compact matrix. The result is a material with high mechanical strength and anisotropic light transmission that is ideal for applications like smart windows.
To add solar control functionality, the surface was coated with W-VO2 nanoparticles, giving the bamboo thermochromic properties that can regulate sunlight based on temperature.
The materials involved in the process included flattened and natural bamboo boards, chloroform, polyethylene glycol (PEG 8000), W-VO2 nanoparticles, and poly(lactic acid) (PLA).
How the Material Was Made
The preparation of W-VO2 nanoparticles began with a stoichiometric mix of aqueous sodium tungstate and vanadyl sulfate, followed by a controlled addition of ammonium bicarbonate over 1.5 hours with constant stirring. After an additional hour, the precipitate was filtered, washed with ethanol and deionized water to remove sulfates, and vacuum-dried at 40?°C for four hours.
The final step involved calcining the dried powder under nitrogen flow at 300–800?°C in a quartz tube, resulting in W-VO2 nanoparticles with over 95 % yield.
To prepare transparent bamboo, raw samples were treated with a peroxyacetic acid solution at 60?°C for six hours to remove lignin. After extensive washing, the samples were pressed at 20?MPa between filter papers and dried at 35?°C for 24 hours, which meant that optically transparent bamboo sheets could finally be yielded.
For the thermochromic coating, W-VO2 nanoparticles were ultrasonically dispersed in chloroform, and a mix of PLA and PEG was dissolved into the solution under magnetic stirring. This blend was blade-coated onto the transparent bamboo to form a ~10?μm thick film, then air-dried. The same method was used to coat glass substrates for comparison.
What the Results Showed
The transparent bamboo developed through this method displayed impressive performance on multiple fronts. Directional pressing and delignification created a dense, aligned structure that dramatically improved mechanical properties: tensile strength rose from 288 MPa to 870 MPa, and flexural strength doubled from 138 MPa to 276 MPa. It also showed notable gains in toughness and hardness over untreated bamboo.
Optically, the bamboo offered 78 % visible light transmittance and more than 90 % haze, which is ideal for soft, even daylight distribution. Its thermal insulation properties made it suitable for energy-efficient building applications. But what sets this material apart is its ability to modulate solar radiation dynamically. Thanks to the W-VO2 coating, the bamboo is able to respond to temperature changes. For example, above ~31.4?°C, it blocks near-infrared light to reduce heat gain; below that threshold, it lets sunlight through to help warm interior spaces.
In field tests, the thermochromic bamboo was found to outperform traditional glass in managing heat in hot regions of China. It achieved a solar modulation ability of 9.7 % and helped reduce indoor cooling loads, translating into real energy savings.
Beyond performance, the environmental footprint of this material is notably smaller. Life cycle assessments showed the thermochromic transparent bamboo had lower impacts across several key indicators, including global warming potential, fossil resource use, and human health, compared to conventional materials like glass and cement.
Conclusion
This research points to an exciting step forward in how we think about building materials.
Transparent bamboo brings together strength, clarity, and smart temperature control all in a material that’s renewable and biodegradable. It not only performs well but also helps cut down energy use and carbon emissions, making it a practical and more sustainable alternative to traditional glass.
Journal Reference
Li, Z., et al. (2025). Sustainable Transparent Bamboo/W-VO2 Composites for Solar Modulation and Energy-Efficient Buildings. Journal of Bioresources and Bioproducts. DOI: 10.1016/j.jobab.2025.11.001, https://www.sciencedirect.com/science/article/pii/S2369969825000702
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