Studies on the thermal degradation of thermosetting polyimides and their composites

Abstract: Thermosetting polyimides, based on 4,4’-(hexafluoroisopropylidene)diphthalic anydride (6FDA) backbone, can be used for resin transfer molding (RTM) manufacturing of carbon fiber polymer composites. The high glass transition temperature and good thermal stability of the 6FDA polyimides place them at the forefront of research for high-temperature aerospace applications.The thesis concentrates on the thermal oxidative stability of 6FDA polyimides and their composites, i.e. the problems that arise when oxygen is present in the atmosphere in addition to elevated temperatures (>288°C). Thermal oxidative degradation is dependent on oxygen diffusion during exposure and hence manifests as a layer, or shell, starting at the surface of the material and growing inward into the bulk. A good understanding of the properties and behavior of the oxidation layer is crucial for proper component design and risk analysis.The appended papers investigate further the subject of thermal oxidation on both polymer and composite levels, using techniques such as X-ray computed microtomography and fracture toughness.