Aging Behavior of Polymeric Absorber Materials for Solar Thermal Collectors

Susanne Kahlen

Research output: ThesisDoctoral Thesis

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Plastics offer a high potential for use in solar thermal absorbers, in particular also for flat plate collectors. For such applications, high temperatures in air and water represent the most harmful service conditions. Hence, the investigation of aging phenomena in such materials at elevated temperatures in water and air is of enormous importance to characterize their performance and to identify possible limitations. So far, no comprehensive characterization has been reported, and therefore the main objective of this dissertation was to investigate the aging behavior of plastics for solar thermal absorbers using various methods of polymer science. Special focus was given to the determination of physical and chemical aging processes, and to the establishment of structure-property relationships and of correlations between the results obtained on the level of laboratory specimens, and the sub-component and component level. For this dissertation, eight different potential polymers for solar thermal absorbers, including four engineering-type plastics (a blend of polyphenylene ether and polystyrene (PPE+PS), polycarbonate (PC), high-impact polyamide 12 (PA12-HI), high-temperature PA12 (PA12-HT)) and four commodity-type plastics (two types of crosslinked polyethylene (PE-X1, PE-X2), two types of polypropylene (PP-1, PP-2)), were selected. According to northern climate conditions, 140 °C in air (during stagnation) and 80 °C in water (during operation) with aging times up to 500 h and 16000 h, respectively, were assumed as typical aging conditions corresponding to an accumulated lifetime of 20 year in service. On the laboratory specimen level, two different analytical methods (differential scanning calorimetry (DSC) and size exclusion chromatography (SEC)) and a mechanical method (monotonic tensile test) were applied to investigate the aging behavior. On the sub-component and component level, DSC and a mechanical indentation test were performed. Furthermore, for three selected polymers (PPE+PS, PC, PP-2) three different lifetime prediction models based on the Arrhenius relationship and results obtained on the laboratory specimen level were used to determine service time endurance limits. In any case, as this dissertation is the first polymer science based study of the aging behavior of potential material candidates for solar thermal absorbers, further investigations are necessary to substantiate all of the results obtained prior to applying these materials to commercial products.
Translated title of the contributionAlterungsverhalten von polymeren Absorbermaterialien für solar-thermische Kollektoren
Original languageEnglish
  • Rekstad, John Bernhard, Assessor B (external), External person
  • Lang, Reinhold, Assessor A (internal)
Publication statusPublished - 2009

Bibliographical note

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  • solar thermal absorber
  • aging behavior
  • physical and chemical aging
  • lifetime modeling

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