Biodegradable Metafilm Offers Breakthrough in Sustainable Cooling

By Muhammad OsamaReviewed by Laura ThomsonJul 2 2025

A recent study published in the journal Cell Reports Physical Science presented a biodegradable metafilm made from poly(lactic acid) (PLA) for durable and efficient passive radiative cooling (PRC). This bioplastic cooling metafilm (BPCM) combines high solar reflectance, strong thermal emission, ultra-low thermal conductivity, and excellent durability, offering a sustainable solution to reduce energy consumption while addressing the environmental impact of conventional cooling technologies.

The Role of Passive Radiative Cooling Technology

Global warming and climate change have increased the need for sustainable cooling solutions. Conventional devices such as air conditioners and refrigerators consume significant amounts of energy and release greenhouse gases, worsening environmental problems.

In this context, PRC offers a clean alternative by allowing surfaces to cool naturally, reflecting sunlight and releasing heat into outer space without using electricity. However, existing PRC materials often suffer from poor durability and environmental issues from non-biodegradable components or toxic nanoparticles.

Bioplastics like PLA are eco-friendly options due to their biodegradability, but typically lack long-term stability for outdoor use. This research paper addresses these challenges by developing a durable PLA-based metafilm that delivers strong cooling performance while remaining environmentally sustainable.

Introducing a Metafilm with Advanced Structural Control

Researchers developed a BPCM fabricated primarily from PLA, a biodegradable and commercially available biopolymer derived from renewable sources. They employed a scalable low-temperature two-step phase separation (LTPS) technique to create a ∼500 μm-thick metafilm with a bi-continuous porous microstructure.

The process involved dissolving poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) in chloroform at a 3:1 ratio, followed by incubation at -20 °C to enhance molecular chain entanglement. Phase separation was then induced using ethanol at the same low temperature, followed by drying at room temperature.

This cold treatment allowed the formation of strong crystalline structures known as stereocomplex (SC) crystals between PLLA and PDLA chains. These SC crystals improved mechanical strength, thermal stability, and durability without compromising biodegradability, achieving a melting point of 218.5 °C and a crystallinity of 29.7%.

Compared to conventional room temperature phase separation (RPS) and direct low-temperature phase separation (LPS), the LTPS process produced a finer, more interconnected porous network.

Characterization was performed using several techniques, including scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), atomic force microscopy (AFM), polarization optical microscopy (POM), and rheological analysis.

These analyses confirmed a uniform porous architecture, high crystallinity, and improved durability of the metafilm, which significantly outperformed films made by conventional phase separation methods.

Superior Optical, Thermal Performance, and Environmental Stability

The LTPS-fabricated BPCM demonstrated excellent optical and thermal properties for PRC, achieving a solar-weighted reflectance of 98.7% and mid-infrared emittance of 96.6% (8-13 µm).

Its ultra-low thermal conductivity of 0.049 W m^-1K^-1, resulting from a high porosity of 84.6%, minimizes heat gain from the environment and enhances cooling efficiency.

Outdoor evaluations conducted in Zhengzhou, China, showed a maximum sub-ambient cooling of 9.2 °C at midday and an average daytime cooling of 4.9 °C, with nighttime cooling averaging 5.1 °C. The BPCM significantly surpassed metafilms made via conventional RPS and LPS techniques, which had lower reflectance, emittance, and cooling capacity.

Durability tests confirmed the metafilm’s resilience. After immersion in acid for 120 hours and accelerated ultraviolet (UV) aging equivalent to 8 months of sunlight, the BPCM retained its hydrophobicity, high reflectance, and structural integrity. Interestingly, the SC crystallinity slightly increased post-aging, enhancing thermal stability and acid resistance.

EnergyPlus simulations indicated that applying BPCM as an external building material could reduce annual cooling energy consumption by up to 20.3%, particularly in cities like Lhasa, China.

Additional outdoor tests in Adelaide, Australia, verified consistent cooling performance after environmental exposure, achieving temperature reductions of 5 °C following acid treatment and 6.5 °C after UV aging. This durability outperformed many existing PRC materials, which often degrade without protective coatings.

Impact on Sustainable Building and Climate Adaptation

The bioplastic metafilm addresses key challenges by combining sustainability, durability, and high performance for passive radiative cooling. Its biodegradable PLA-based composition provides clear environmental advantages over petroleum-based polymers and nanoparticle-infused composites, contributing to plastic pollution and toxicity concerns.

Integrating BPCM into buildings, roofing, or exterior coatings can significantly reduce cooling loads, energy costs, and carbon footprints in residential and commercial structures. Its acid rain and UV degradation resistance ensures long-term use in various climates. Beyond architecture, the metafilm is also suitable for personal cooling textiles, automotive coatings, and outdoor equipment, supporting climate adaptation and energy efficiency.

Toward Next-Generation Eco-Friendly Cooling

The BPCM represents an effective approach to developing a bioplastic metafilm with a bi-continuous porous structure and high stereocomplex crystallinity. Its durability under acidic and UV conditions ensures stable cooling performance without needing protective coatings. The scalable LTPS fabrication method provides a practical pathway for the commercial production of sustainable, energy-efficient passive cooling materials.

Future work should optimize the microstructure, incorporate other eco-friendly materials, improve polymer blends, and conduct real-world performance evaluations. Overall, this metafilm marks a significant advancement in clean technology, offering energy savings, reduced environmental impact, and long-term stability for sustainable climate solutions.

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