Surface topography and cooling effects in poly(vinyl chloride) (PVC)/titanium dioxide (TiO2) composites exposed to UV-irradiation

Abstract

Rutile titanium dioxide (TiO2), at different amounts (0, 1, 3, 5, 8 and 10 phr), was used to prepare PVC/TiO2 composites as cool materials. Exposure to the ultraviolet (UV)-irradiation at 65 °C (black-panel thermometers) with a xenon arc as the light source (0.51 W/(m2 nm), 340 nm) for 200, 400 and 600 h resulted in the formation of polyene structure in PVC and causing discoloration. Besides, atomic force microscopy and roughness measurements were used to examine the changes in surface topography and roughness before and after UV-irradiation. Ethylenic index was used to characterize the aging degree of composites. The contact angle value of composites became smaller and their polarity increased after exposing to UV-irradiation, but the presence of TiO2 effectively prevented this process. In addition, exposure to UV-irradiation had little effect on the reflectance of PVC/TiO2 composites over the whole solar wavelength range (200–2500 nm), especially in near infrared (NIR) region (700–2500 nm). This allowed the TiO2-loaded samples to display an excellent cooling property whether indoors or outdoors. The addition of higher quantities of TiO2 led to higher efficiency of the cooling effect. In general, this study provides strong support for the property of long-term outdoor use of PVC/TiO2 composites with high solar reflectance and excellent cooling performance.