Processing, Dynamic Studies and Properties of Exfoliated Aerospace Epoxy-Organoclay Nanocomposites
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Processing, Dynamic Studies and Properties of Exfoliated Aerospace Epoxy-Organoclay Nanocomposites Chenggang Chen1 and David Curliss2 1 University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0168, U.S.A. 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, WPAFB, OH 45433, U.S.A. ABSTRACT Epoxy nanocomposites were prepared from the montmorillonite after organic treatment with a high Tg epoxy resin (Shell Epon 862 and curing agent W). Investigation of the rheological characteristics showed that the addition of clay to the resin did not significantly alter the viscosity or cure kinetics and that the modified resin would still be suitable for liquid composite molding techniques such as resin transfer molding. DSC was performed to study the kinetics of the curing reactions in the modified resin. An in situ small-angle x-ray scattering (SAXS) experiment was used to try to understand the structural development during cure. Based on the in situ SAXS data, structural changes were monitored in real time during cure and analyzed. Results from wide-angle x-ray diffraction, SAXS, and transmission electron microscopy of the polymer-silicate nanocomposites were used to characterize the morphology of the layered silicate in the epoxy resin matrix. The glassy and rubbery moduli of the polymersilicate nanocomposites were found to be greater than the unmodified resin due to the high aspect ratio and high stiffness of the layered silicate filler. The solvent absorption in methanol was also slower for the polymer-silicate nanocomposites. INTRODUCTION Conventional composite materials are materials with a macroscopic combination of two or more distinct materials, having recognized interface between them [1]. They have been widely used in construction, transportation, electronics and consumer products. Composites with at least one solid phase with a dimension in the range of 1-100 nm can be defined as nanocomposites [2, 3]. Polymer-layered silicate nanocomposites are new hybrid materials of polymers with nanometer-thickness layered silicates. Due to the unique nanometer-size dispersion of the layered silicates with high aspect ratio and high strength in the polymer matrix, these materials generally exhibit improvements in properties even at low loading of layered silicate. These properties can include mechanical performance, ablation performance, thermal stability, barrier performance, and flame retardancy [4-7]. Layered silicates are abundant and important minerals in geological environments at or within roughly 20 km of the Earth surface [8]. There are many types of sheet silicates including clay mineral. The most widely used layered silicate for the nanocomposites is montmorillonite. Natural montmorillonite is constructed of repeating TOT layers composed of two silica tetrahedral sheets fused to an edge-shared octahedral sheet of alumina. The physical dimensions for these silicate sheets are around one hundred to several hundred nanometer in lateral and 1-nm in thickness. However, the individua
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