Aerospace Applications for Epoxy Layered-Silicate Nanocomposites
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Research on polymer nanocomposites based on layered silicates has exploded over the last decade, ever since the pioneering work of the organoclay–nylon nanocomposite by Toyota. The dispersion of the silicate nanolayer with its high aspect ratio, large surface area, and high stiffness within a polymer matrix results in significant improvement of the properties of polymeric materials, including mechanical properties, barrier properties, resistance to solvent swelling, ablation performance, thermal stability, fire retardancy, controlled release of drugs, anisotropic electrical conductivity, and photoactivity. Layered-silicate nanocomposites have great potential for applications, ranging from automotive and aerospace to food packaging and tissue engineering. Cost and processability are as important to many applications as the property improvements.
Epoxy materials have been widely used in adhesives, coatings, electronic encapsulants, and advanced composites. Since the Pinnavaia group first extended the nanocomposite concept to epoxy systems, extensive research on layered-silicate epoxy nanocomposites has been carried out. This paper is the summary of some of the past research and latest research in our group, which focus on layered-silicate epoxy nanocomposites for aerospace applications. The aerospace epoxy used in the study is made from Shell Epon 862 with Epi-Cure curing agent W. This epoxy system has a high glass transition temperature (Tg), good mechanical and physical performance characteristics, and low viscosity, and involves non-4,4′-methylenedianiline aromatic amines. The compatibility of organoclays with aerospace epoxy resin and the preparation of the nanocomposite were studied. Small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to characterize the morphology of the nanocomposites. The properties of the nanocomposite, including the dynamic and static mechanical property and survivability in aggressive environments such as oxygen plasma, were measured. The integrated study of in situ SAXS, differential scanning calorimetry (DSC), and rheology provides information about the viscosity development and processing window, as well as the morphology development and exfoliation mechanism. Morphology development behavior for the epoxy nanocomposites as a function of curing agents, including Jeffamine and curing agent W, is discussed. In addition, epoxy nanocomposites as primer layer for aircraft coatings for improved anticorrosion properties are described.