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Heatwaves have become a defining feature of modern summers, with the World Meteorological Organization noting the past seven years as the hottest on record. As urban areas heat up, the reliance on air conditioning grows, further exacerbating carbon emissions and climate change. But what if there was a way to stay cool without electricity? Researchers from Zhengzhou University and the University of South Australia have made a breakthrough with a biodegradable film that can cool surfaces without the need for power.
The Innovative Cooling Film
This groundbreaking metafilm is a product of collaboration between researchers from Zhengzhou University and the University of South Australia. Termed a ‘bioplastic metafilm,’ this material can reflect nearly 99% of the sun’s rays and cool surfaces by up to 16.6°F (9.2°C), even under direct sunlight. According to Yangzhe Hou, a PhD student from UniSA, the metafilm offers a green alternative to traditional air conditioning, which significantly contributes to carbon emissions. The film achieves its cooling effect by reflecting solar radiation and allowing heat within buildings to escape into space.
Made from polylactic acid (PLA), a plant-based bioplastic, the film employs a low-temperature separation technique to create a microstructure that effectively reflects sunlight while allowing heat dissipation. This innovative approach requires no electricity or mechanical systems, distinguishing it from conventional cooling technologies that rely on environmentally harmful petrochemicals.
The Science Behind the Film
The metafilm’s creation involves a low-temperature two-step phase separation method. By dissolving PLA in a solution, cooling it to -4°F (-20°C) for 12 hours, and then drying it at room temperature, the team achieved a unique bi-continuous pore structure. This structure is pivotal, as it enhances both reflectivity and thermal emission while maintaining durability: a common challenge for biodegradable materials.
Many eco-friendly cooling films degrade rapidly in adverse conditions like acid rain or ultraviolet radiation. However, this metafilm maintains its performance even after 120 hours in strong acid and extensive UV exposure. Its hydrophobic properties ensure water repellency, and its cooling effect remains robust, dropping temperatures by up to 11.7°F (6.5°C) after exposure to harsh conditions. This scalability and durability make it a promising solution for reducing reliance on fossil fuels.
Real World Impact and Future Potential
Field tests conducted in China and Australia demonstrated the metafilm’s efficacy. During daylight hours, it lowered temperatures by an average of 8.8°F (4.9°C), and at night, it maintained a 9.2°F (5.1°C) drop. The researchers utilized EnergyPlus software to simulate energy savings, revealing up to 20.3% annual cooling energy reduction in cities like Lhasa, China.
The metafilm outperformed other radiative cooling materials, such as PLA aerogels and ceramic composites, in solar reflectivity and thermal conductivity. With an ultra-low thermal conductivity of 0.049 W/mK, it slows heat transfer into buildings, offering significant energy savings. Its potential applications extend beyond buildings to farm equipment, vehicles, and even medical uses, thanks to its durability and biodegradability.
The Role of Crystal Structures
The metafilm’s strength lies in its internal crystal structures. PLA can form various crystals, but the stereo-complex (SC) crystals formed in this film provide additional strength and thermal stability. These SC crystals melt at about 424°F (218°C), making the film resilient to high temperatures.
With an SC crystallinity of nearly 30%, the film boasts exceptional stability. Even after exposure to acid and UV radiation, the SC crystallinity slightly increases, enhancing the structure’s strength. This durability addresses a significant challenge in the field: combining high cooling performance with long-term environmental resilience.
Exploring a Cooler Future
As the climate crisis intensifies, energy-efficient solutions that enhance comfort are essential. This metafilm represents a significant step toward that goal, offering a scalable, durable, and environmentally friendly alternative to traditional cooling methods. By reducing the reliance on petroleum-based plastics and eliminating the need for electricity, it cuts greenhouse gas emissions linked to power use.
With potential applications ranging from skyscrapers to electronic devices, this metafilm could become a versatile tool in combating climate change. As researchers continue to explore commercial production and broader uses, the question remains: how will this innovation shape the future of sustainable cooling solutions?
