Flexible and Degradable Poly(Vinyl Alcohol)-Based Film for Passive Cooling Applications

Passive radiative cooling materials with high solar reflectance efficiently alleviate the problem of the greenhouse effect and global warming through less heat accumulation, while environmentally friendly and degradable properties are desired because of human environmental awareness. However, sustainable passive radiative cooling materials have not been extensively studied. Herein, degradable and water-soluble poly(vinyl alcohol) (PVA) was applied as the polymer-matrix, and then, it would ultimately degrade into water and carbon dioxide at the end of life. Meanwhile, titanium dioxide (TiO2) with nano- and micron-scale particle sizes was utilized to investigate the effect of their simultaneous application on solar reflectance and cooling property for high efficiency. In the present study, the eco-friendly film was prepared via the casting method. As a result, the simultaneous application of 3 wt % nano- and 7 wt % micron-scale TiO2 contributes to the higher visible light reflectance (RVIS) of 81.3%, near-infrared light reflectivity (RNIR) of 66.0%, and solar reflectance (RS) of 70.6%. Simultaneously, the thermal emissivity at the atmospheric window (8–13 μm) reaches to the value of 0.96, while the solar reflectance index values are higher than 87. Compared with PVA, this white film presents cooling capability, approximately reaching 20 °C below the ambient temperature. Thus, this passive radiative cooling film with high solar reflectance and high thermal emissivity presents advantages in energy savings and maintains sustainable development, which can be applied in the field of foldable sunshade materials for sunroom or windows.