A super-cooling solar reflective coating with waterborne polyurethane for asphalt pavement

Abstract

To construct highly cooling solar reflective coatings with excellent abrasive resistance, a crosslinkable absorbing heat waterborne polyurethane (WPU) was synthesized and used to prepare a solar reflective coating for asphalt pavement. The super-cooling effect of WPU based on solar reflective coating was evaluated by comparing to that of waterborne epoxy (WEP) and polyacrylate emulsion (WMMA). Due to formation of numerous PBA microcrystals in WPU matrix, the heat absorbing behavior of WPU was confirmed by DSC results. The melting of microcrystals occurred at -2–105 °C, and the fusion enthalpy was 48 J/g. Although the solar reflective coatings based on the three resins had similar total reflectance, according to temperature experiment, WPU reflective coating (WPURC) still had the best cooling performance and could reduce the inner temperature of asphalt concrete by 7–11 °C. In the presence of numerous PBA microcrystals, WPURC showed effective and stable super-cooling effect during cyclic temperature experiment. Additionally, during abrasive test, WPURC not only had excellent anti-abrasive performance, but also effectively reduced threat of abrasion to cooling performance. Herein, the heat absorbing WPU constituted a major breakthrough for efficient cooling and functional durability of the reflective coating.