Aging behavior of polymeric absorber materials for solar thermal collectors

Transcription

1 Aging behavior of polymeric absorber materials for solar thermal collectors Susanne Kahlen, Gernot M. Wallner, Reinhold W. Lang July, 211 Introduction Plastics based collectors 2 SOLARNOR all-polymeric collector During operation Application in Northern Europe Glazing (extruded, PC) Absorber (extruded, PPE+PS) Out of operation, draining phase System conditions: operation - water at 8 C stagnation - air at 14 C only few comparable systems with plastics available No comprehnsive and scientifically founded understanding of the aging behavior and the long-term stability of plastics for solar thermal absorber applicatons 2

2 Methodology Testing pyramid Structure-property-performance pyramid Various levels of material state 3 levels of characterization/testing Outdoor exposure Laboratory aging System level Component level: absorber sheet Absorber outdoor exposure Absorber laboratory aging Extruded polymer films Specimen level (compounds, semi-finished product): standard test specimens Film specimens laboratory aging amorphous semi-crystalline Constituent level (polymer, additives): raw material characterization 3 Methodology Materials and exposure conditions Designation Polymer type Commercial designation Material supplier PPE+PS Polyphenylene ether Noryl EN 15SP Sabic Innovative Plastics polystyrene blend PC Polycarbonate Makrolon 313 Bayer Material Science PA12 Polyamide 12 Grilamid L25H, Grilamid L25ANZ PP Polypropylene random copolymer Beta-PPR RA75, RA13E-8427 EMS-CHEMIE Borealis Polyolefine System level: Outdoor exposure under stagnation (northern climate): 1 winter, ½ summer, 1 summer, 1 year, 2 years Specimen and component level: Laboratory aging: - in air at 14 C up to 5 h (northern climate) - in water at 8 C up to 16 h 4

3 Methodology Characterization and Testing 1 Specimen level Tensile Testing Laboratory sepcimen 5 4 Digital image correlation system Video extensometer DSC and SEC analysis strain, % Characteristic parameter for aging: strain-to-break ( B ) Morphology and thermal properties (e.g., crystallinity, T m, T g, T ox ) Weight average molecular mass 5 Methodology Characterization and Testing 2 Component level Indentation testing 6 4 h 2h 4h 6h 8h water, 8 C 2 Absorber sheet sepcimen DSC analysis load, N 6 4 h 125h 25h 375h 5h air, 14 C 2 F T Laboratory aging indentation, mm I B Characteristic parameter for aging: indentation at break (I B ) Morphology and thermal properties (e.g., endothermic and exothermic effects, T g, T ox ) 6

4 Results Specimen level: Aging behavior of PPE+PS PPE+PS - Effect of exposure to hot water at 8 C SEC results 7 2 PPE+PS, water 8 C PPE+PS, PPE 6 18 water 8 C PS 16 5 chain scission of PS h 8 2h chain scission of PPE h strain, 1% exposition time, h DSC: no physical aging detected wt. avg. molar mass, kg/mol 7 Results Specimen level: Aging behavior of PPE+PS PPE+PS - Effect of exposure to hot air at 14 C PPE+PS, air 14 C 2 h 1 25h 5h strain, % exposition time, h DSC: physical aging (enthalpy relaxation) detected wt. avg. molar mass, kg/mol 8 SEC results PPE+PS, air 14 C PPE PS cross-linking of PPE chain scission of PS 8

5 Results Specimen level: Aging behavior of PA12 PA12 - Effect of exposure to hot water at 8 C 6 4 PA12, water 8 C 2 h 2h 16h exo DSC thermograms PA12, water 8 C decrease in oxidation temp h 2h 16h strain, 1% temperature, C SEC: slight decrease in weight average molecular mass 9 Results Specimen level: Aging behavior of PA12 PA12 - Effect of exposure to hot air at 14 C 6 PA12, air 14 C exo DSC thermograms PA12, air 14 C 4 2 h 25h 5h strain, 1% secondary crystallization temperature, C SEC: slight increase in weight average molecular mass initially h 25h 5h 1

6 Results Specimen level: Aging behavior of PP PP - Effect of exposure to hot water at 8 C 5 4 PP, water 8 C exo DSC thermograms PP, water 8 C h 2h 16h 3 2 h 1 2h 16h strain, 1% temperature, C SEC: no significant change in weight average molecular mass 11 Results Specimen level: Aging behavior of PP 6 5 PP - Effect of exposure to hot air at 14 C PP, air 14 C exo DSC thermograms PP, air 14 C h 1 25h 5h strain, 1% temperature, C h 25h 5h SEC: no significant change in weight average molecular mass 12

7 Results Specimen vs. component level: PPE+PS strain at break, % indent. at break, % specimen level air, 14 C component level aging time, h 13 Results System level vs. Component level: PPE+PS ind. at break, % ind. at break, % Outdoor aging A=.131 y=1*exp(-a*x) R 2 = cum. irradiation, kwh/m 2 A=.437 R 2 =.845 Laboratory aging aging time, h System level Component level 14

8 Conclusions and Outlook Conclusions: Scientific approach was corroborated efficient material screening for solar-thermal absorbers is possible on specimen level -PP and PA12 grades exhibited better long-term stability compared to the PPE+PS reference grade AVENTA (Oslo, N): PPS for absorber used Outlook: Competition with conventional solar thermal collectors by the use of commodity plastics (e.g., PP, PE) modified to the exisiting application and/or filled with fillers (carbon, etc.) Modification of solar thermal system to reduce max. stagnation temperature by design or by overheating protection (e.g., functinal polymers) 15