The aging behavior of two commercial conductive polythioether sealants

Abstract

Conductive polythioethers are widely used sealants where both environmental and electromagnetic radiation sealing is required. The aging behavior of these sealants is of critical interest in industry since hardware built using these sealants may need to function and the sealant provide a satisfactory seal for years, if not decades, after the hardware is initially built and the sealant initially applied. Accelerated oven aging data at 65, 75 and 85 °C for time periods ranging from 73 to 1773 h on two commercial conductive polythioether sealants are discussed. Adhesion efficacy is quantified by changes in lap shear per ASTM D1002 . Electromagnetic interference sealing efficacy is quantified by changes in volume resistivity per MIL-STD-883. The two sealants show similar aging behavior for conductivity in that volume resistivity fell dramatically upon accelerated oven aging. The lap shear increased significantly for only one of the two sealants, indicating that the supplier recommended cure protocol for that sealant did not lead to full cure. Instead, the cure progressed further during accelerated oven aging. This caused the lap shear to increase up to around 40% as compared to unaged samples. The aging temperature was limited to 85 °C out of concern that a higher temperature may change the degradation mechanism from that prevailing at room temperature, RT [23C], which can lead to erroneously high life predictions. The aging time was limited to 1773 h [74 days] due to practical, equipment and experimental constraints. It is expected that the adhesive and conductive efficacy after 30 years at 23 °C should be no worse [and perhaps significantly better] than upon initial build.