COOLSUN: a preliminary study of “cool” properties of organic pigments

Approximately 50% of the solar energy reaching the earth is emitted in the near infrared region (NIR), not detectable by human eye. The absorption by an object in the NIR causes an increase of its temperature1. The pigments that interact with the NIR portion of the solar spectrum (i.e. between 700 and 1600 nm) without absorbing it are called NIR-reflecting, and their use reduces the heating of the treated substrates2. The NIR-reflective property is useful in applications where solar heating must be attenuated, such as leather goods, greenhouse coverings ,roofing and transporting of heat-sensitive materials3. Today, NIR reflectivity is obtained with the use of inorganic pigments (TiO2, metal oxides and complexes) that are expensive and, in some cases, toxic1. The key to obtain innovative coatings is then the production of organic NIR-reflective pigments to overcome problems related to costs, environmental impact, efficiency and color index of the current inorganic pigments on the market4. The goal of our work is the development of innovative products containing organic-based NIR reflective and/or NIR transparent pigments. In this preliminary phase of our project we focused on the study of the "cool" properties of commercial pigments in order to be able to design and develop thermo- and photostable organic pigments, able to reflect the radiation in the NIR. The pigments were initially dispersed in a polymeric matrix, the produced mixture was applied on white (maximum reflectance) and black (maximum absorption) test panels. The percentage reflectance of two test panels (black and white) for each pigment was determined using a UV-Vis-NIR spectrophotometer. The pigment/matrix mixtures were then applied on leather samples for the determination of the cool properties through the use of a thermal imaging camera.