Collector sealants and breathing. Final Report, 25 September 1978-31 December 1979

Abstract

An extensive literature survey fo~lowed by laboratory screening tests was used to select candidate Class PS (preformed rubber seal~) and Class SC (sealing compounds or caulks) elastomers for more comprehensive laboratory testing to assess their performance capabilities under the harsh environment of a thermal solar collector cell. Tests employed incluqed thermal aging in air, hydrolytic stability, weathering resistance, corrosion of metallic substrates, ozone resistance and fungal susceptibility. Since the most hostile factor in the solar collector cell environment is long-term exposure to elevated temperatures in air, the thermal stability testing was extended to the monitoring of change in several physical properties during thermal aging in air. These included compression set, tensile characteristics, hardness and weight loss. Although none of the PS.elastomers tested was found to be entirely satisfactory, the fluorocarbon (Viton) displayed the best durability and thermal stability overall. The silicones were second best. Unfortunately, the fluorocarbons tend to exhibit excessive low temperaturA compression set, a characteristic which could be a serious problem in geographic zones having relatively cold winters. The silicones show very poor resistance to compression set on thermal aging and, while the fluorocarbon is considerably superior in this respect, it nevertheless displays undesirably high values. The polyacrylate and acrylic copolymers and one of the ethylenepropylene terpolymers (EPDM-Nordel) were the best of the intermediate temperature elastomers. Except for resistance to compression set, these materials were inferior to the silicones in thermal stability. The other EPDM compounds and butyl rubber were considerably inferior to the three compositions just mentioned.