Fluorocarbon and PTFE Thermodegradation and Contamination Modeling in a Space Habitat

The products of thermodegradation of fluorocarbon polymers (found in electrical insulation) will be toxic to space habitat crews, and the monitoring and detection of such contaminants are important to space environmental health. Experiments are therefore being performed on the thermodegradation of a liquid perfluoroalkane mixture (consisting of perfluorohexanes, C₆F₁₄, and −5% perfluoropentane, C₅F₁₂), similar in structure to polytetrafluoroethylene (PTFE - Teflon), in atmospheres of varying oxygen concentration. PTFE is a common material used on space vehicles for insulation of wires. When PTFE is thermally degraded, such as from the overheating of a wire and subsequent smoldering of the insulation, it may produce toxic compounds ranging from carbonyl fluoride and hydrogen fluoride through perfluorinated aromatic compounds to ultrafine particles. The liquid perfluoroalkane (PFA) mixture is vaporized in the presence of helium, which is used as a carrier gas in this experiment and is acting in place of nitrogen as the non-reactive portion of the atmosphere. The helium and perfluoroalkane vapor can then be mixed with oxygen to yield atmospheres of known concentrations. The mixture is fed into a tube reactor furnace where it is thermally degraded. The resulting thermodegradation products are analyzed by combined gas chromatography/mass spectrometry (GC/MS) for composition. This analysis allows the characterization of the reaction products for simulation models and monitoring and detection systems in space habitats.