Aging behavior of polymeric materials for solar thermal absorber applications

This paper focuses on the description of the aging behavior of selected polymeric materials for solar thermal absorbers. Based on the experiences with the Solanor (R) all-polymeric collector stagnation temperatures of 140 degrees C in air and maximum operating temperatures of 80 degrees C in hot water were assumed. Two amorphous polymers including the currently used absorber material Noryl (R) (a poly(phenylene ether)/polystyrene (PPE+PS) blend) and a semi-crystalline polymeric material were investigated. The purpose of this paper is to analyze the aging behavior of the selected polymers. Therefore extruded specimens were exposed to hot air at 140 degrees C and hot water at 80 degrees C for various aging times. The aging behavior was characterized by mechanical (monotonic tensile test) and analytical methods (differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and infrared spectroscopy in attenuated total reflection mode (ATR). It was found that ultimate mechanical properties, oxidation temperatures measured by DSC and molecular weight distributions (measured by SEC) are sensitive parameters indicating degradation. In general, the investigated amorphous polymers showed a more significant degradation behavior than the semi-crystalline polymer.