Scientists have engineered a plant-based cooling film that can lower building temperatures by nearly 10 degrees Celsius without consuming any energy.
The biodegradable material reflects 98.7% of sunlight while allowing heat to escape into space, potentially reducing urban cooling costs by one-fifth.
The research, published in Cell Reports Physical Science, addresses a growing challenge as global temperatures rise and cities seek sustainable alternatives to energy-intensive air conditioning systems.
How the Cooling Technology Works
The bioplastic metafilm operates through passive radiative cooling, a process that mimics how the Earth naturally sheds heat into space. Unlike conventional cooling materials that rely on petroleum-based polymers, this film uses polylactic acid (PLA), a biodegradable plastic derived from plant sources like corn or sugarcane.
Researchers from Zhengzhou University and the University of South Australia created the material using a specialized low-temperature separation technique. This process generates a porous, bi-continuous structure that optimizes light scattering while maintaining the film’s complete degradability.
“The material reflects nearly all solar radiation but also allows internal building heat to escape directly into outer space,” explains UniSA PhD candidate Yangzhe Hou. “This enables the building to stay cooler than the surrounding air, even under direct sunlight.”
Impressive Performance Numbers
Field tests revealed the film’s remarkable cooling capabilities:
- Maximum daytime cooling of 9.2°C below ambient temperature
- Average temperature reductions of 4.9°C during day and 5.1°C at night
- Ultra-low thermal conductivity of 0.049 W m⁻¹ K⁻¹ due to 84.6% porosity
- Cooling power reaching 136 W m⁻² under peak solar conditions
Computer simulations suggest the technology could slash annual cooling energy consumption by up to 20.3% in cities like Lhasa, China. Similar energy savings were projected for other hot climate regions worldwide.
Durability Challenge Solved
Previous biodegradable cooling materials suffered from poor weather resistance, often requiring protective coatings that compromised their environmental benefits. This new film overcomes that limitation through engineered stereocomplex crystals.
The researchers subjected samples to harsh conditions including 120 hours in pH 1 acid solution and ultraviolet exposure equivalent to eight months of outdoor weathering. Even after this punishment, the material retained cooling performance of 5°C to 6.5°C below ambient temperature.
“Unlike conventional cooling technologies, this metafilm requires no electricity or mechanical systems,” notes co-author Dr. Xianhu Liu from Zhengzhou University. The durability stems from the film’s 29.7% stereocomplex crystal content, which provides superior thermal stability compared to regular PLA structures.
Real-World Applications
The technology shows promise across multiple sectors beyond building cooling. Potential applications include transportation, agriculture, electronics thermal management, and even biomedical uses like cooling wound dressings.
“This isn’t just a lab-scale success,” emphasizes co-author Professor Jun Ma from the University of South Australia. “Our film is scalable, durable and completely degradable.”
The manufacturing process appears straightforward enough for commercial production. The team dissolved PLA polymers in chloroform, subjected the solution to controlled crystallization at minus 20 degrees Celsius, then used ethanol to induce phase separation before drying.
Environmental Impact
The innovation addresses mounting concerns about air conditioning’s environmental footprint. Conventional cooling systems account for substantial global energy consumption and carbon emissions, particularly problematic as urbanization accelerates in hot climate regions.
The biodegradable film offers what researchers call a “green alternative that offers high solar reflectance, strong thermal emission, sustainability, and durability.” Unlike ceramic-based cooling materials that raise environmental concerns about nanoparticle toxicity, this plant-derived approach maintains ecological compatibility throughout its lifecycle.
As cities worldwide grapple with rising temperatures and sustainability mandates, this technology could provide a practical pathway toward cooler urban environments without the environmental costs of traditional mechanical cooling systems.
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