Water-based kaolin/polyacrylate cooling paint for exterior walls

Passive daytime radiative cooling (PDRC) coatings for building exteriors are important for building energy efficiency. The development of inexpensive and environmentally friendly radiative cooling (RC) coatings with high adhesion, waterproofing and UV-ageing resistance for building facades remains a highly challenging task. In this work, kaolin/polyacrylate (K/P) paints with excellent overall performance were prepared by spraying method using green waterborne acrylate as binder, cheap and easily available K as filler, and polymethylhydrosiloxane (PMHS) as hydrophobic modifier. The K/P coating has excellent optical properties with a solar reflectivity (SR) of 86.6% and an infrared thermal emissivity (ITE) of 96.8%. RC temperatures of 13.2 degrees C (under shielded condition) and 3.1 degrees C (under open condition) were achieved under direct outdoor daylight with an average irradiance of 778 W/m2. In addition, building energy simulations show that the K/P coating improves heating energy consumption while reducing building cooling energy consumption. However, for most cities in China, the energy savings of the K/P coating on annual building energy consumption is still as high as 6.6%. In particular, the K/P paint used as an exterior wall coating has high adhesion, excellent water resistance, and strong UV ageing resistance, and its optical properties (solar reflectance and infrared thermal emittance) remain unchanged after 10 accelerated ageing cycles. Therefore, the K/P coatings have excellent comprehensive performance and have a wide range of application prospects in the field of green and energy-saving buildings.

Automated summary

In this study, kaolin/polyacrylate (K/P) coatings with excellent optical properties for passive daytime radiative cooling (PDRC) were prepared. The K/P coatings demonstrated high performance in terms of cooling efficiency and energy consumption reduction for buildings. Moreover, the K/P coatings showed strong adhesion, water resistance, and UV aging resistance, making them promising for green and energy-saving buildings.