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 (R
VIS) of 81.3%, near-infrared light reflectivity (R
NIR) of 66.0%, and solar reflectance (R
S) 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.