Characterization of outgassed contaminants from polymeric spacecraft materials

摘要

Silicones and polyolefins are versatile polymeric materials that are often used for spacecraft applications but can produce considerable amounts of non-volatile residue (NVR) contamination. Outgassing properties of a commercial off-the-shelf (COTS) polyolefin tubing and GE RTV615 silicone potting, both of which are known to outgas at high levels, were characterized using ASTM E595 testing and infrared (IR) absorption spectroscopy. The total mass loss (TML) values for the polyolefin tubing varied between 1.8 and 2.5%, while the collected volatile condensable material (CVCM) was between 0.7 and 1.2%. The silicone potting had somewhat lower outgassing levels, with TML values between 1.0 and 1.7% and CVCM ranging from 0.7 to 1.3%. IR analysis of the outgassed residue indicates the materials produce NVR contamination through different mechanisms. The polyolefin tubing, which was composed of a hydrocarbon co-polymer mixed with additives, disproportionately outgassed low-weight molecular compounds containing ester functional groups. In contrast, RTV615 outgassing appeared to proceed through the release of shorter chain silicone polymers or oligomers. Combining outgassing test data with the chemical characterization of NVR residue provides a better understanding of contamination processes and will contribute to the development of more efficient mitigation strategies.