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Daytime radiative cooling semi-transparent roof tile coating from eco-friendly limestone to bio-based hydroxyapatite
Jittrakorn Udomsin1,2, Patawee Sakata1,2, Worawut Rueangsawang1,2
1Advanced Technologies for Energy and Sustainability Lab, School of Materials Science and Innovation, Faculty of Science, Mahidol University, Nakhon Pathom 73170, Thailand.
Abstract:
Daytime passive radiative cooling (DPRC) has attracted considerable interest as an energy-efficient strategy to achieve temperature reduction by reflecting incoming solar radiation while emitting thermal radiation. In this work, we developed a semi-transparent (light transmittance = 71.4% ± 0.8%) waterborne polyurethane/nano-micro calcium carbonate composite (WPU/CaCO3) with 60 wt% loading via ball milling for heat reflection. Later, CaCO3 was replaced with a bio-based hydroxyapatite (HAp) with 50 wt% loading as a durable and sustainable pigment for roof tile coating. The optimized coatings with CaCO3 and HAp were applied on the fiber cement roof tiles, thereby achieving a temperature reduction compared with an uncoated roof tile of approximately 5.3°C and 9.6°C under direct sunlight, respectively, without yellowing appearances after sun exposure for both cases. Additionally, coating on other outdoor materials has been demonstrated. Both WPU/CaCO3 and WPU/HAp show strong potential as a sustainable solution for radiative cooling semi-transparent paints.
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