Black pigmented polypropylene materials for solar absorbers

Polyolefin materials are of high relevance and interest for absorbers of solar thermal collectors with integrated overheating protection. In this work the effect of various black pigments (carbon black (CB) and carbon nanotubes (CNT)) on optical and mechanical properties of PP-RCT grades (Polypropylene-Random Copolymer with special crystalline structure (beta phase) for elevated temperature applications) is investigated. To meet the requirements of high absorbance in the solar wavelength range (> 90%) and enhanced mechanical properties at service temperatures up to 90 degrees C for at least 10 years, black pigmented specimens are characterized in an unaged state by UV/Vis/NIR-spectrometry and tensile testing. The experimental results reveal small nanoscalic carbon black pigments as suitable candidates for the pigmentation and improved absorbance behavior of overheating protected polymeric solar thermal absorbers. The investigated black compounds exhibit integral solar absorbance values between 95 and 96 %. The mechanical properties are significantly affected by the distribution quality of the black pigments. In current research special attention is given to the aging behavior of the developed compounds for solar absorbers. (C) 2012 The Authors. Published by Elsevier Ltd.