Simultaneous Enhancement of Cooling Performance and Durability of the Polymer Radiative Cooler by a High UV-Reflective Polymer Multilayer Film

The development of polymer radiative coolers with easy processing, low cost, and high inherent emissivity has significantly promoted the industrialization process of passive daytime radiative cooling. For excellent outdoor durability, however, the traditional strategy of using UV absorbers inevitably weakens the cooling performance of polymer-based coolers. The introduction of a high UV-reflective layer has been proven to be the most effective strategy to eliminate the negative effects of UV absorption and improve the durability of polymer coolers. Here, a polymer multilayer film (PMF) based on an optical interference mechanism is designed, which exhibits an average reflectance of up to 92.3% in the 300-400 nm UV wavebands. Using a TiO₂-doped epoxy resin (TiO₂-EP) cooler as an example, the solar reflectance of TiO₂-EP increases by 5.43% after introducing PMF as a UV reflective layer. Outdoor tests without shading or convection coverage demonstrate that the average cooling temperature of TiO₂-EP with PMF is further elevated by approximately 1.1 °C. Additionally, its aging rate decreases significantly, and the solar reflectance is 5.08% higher than that of TiO₂-EP without PMF after 120 h of UV aging experiments. Furthermore, PMF obtains a periodic multilayer structure by multilayer coextrusion, which has the advantages of low cost and the ability to be prepared over a large area. PMF is suitable for any type of polymer cooler, providing an efficient method to further promote large-scale application of polymer coolers.