Mechanical and Thermoviscoelastic Behavior of Clay/Epoxy Nanocomposites
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Mechanical and Thermoviscoelastic Behavior of Clay/Epoxy Nanocomposites Jandro L. Abot, Asma Yasmin and Isaac M. Daniel Robert McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, U.S.A. ABSTRACT The study of organic-inorganic nanocomposites has become relevant in recent years since these materials exhibit synergistic properties derived from the two components. Thermosetting polymers like epoxies that have high mechanical properties provide a baseline for further improvement with the addition of nanoclay particles. These nanocomposites can be used as the matrix of a fiber reinforced composite and lead to higher matrix dominated mechanical properties including elastic modulus, strength and fracture toughness. This study concentrates on the mechanical and thermoviscoelastic properties in the glassy regime of nanocomposites prepared by direct mixing. The elastic modulus of the nanocomposites was found to improve with respect to the pure epoxy modulus at the expense of both tensile strength and ductility regardless of clay content. The glass transition temperature was also found to decrease as well. The morphology of the nanocomposites was studied and correlated with the aforementioned properties.
INTRODUCTION Nanocomposites formed by the intercalation or exfoliation of inorganic fillers of the order of 1-100 nm into polymers are of particular interest because of their demonstrated improvement of the physical and mechanical properties relative to the unmodified polymer. Microfillers are used quite extensively but the use of nanofillers is limited because of dispersion problems and viscosity build-up related to strong interparticle interactions. Layered silicate/polymer nanocomposites and clay/epoxy nanocomposites in particular have been studied over the last decade [1]. The morphology of these materials plays a key role and many papers have been written about the characterization of nanocomposites in the nanoscale describing the different layer separations. However, a characterization in the mesoscale and microscale is necessary to determine the orientation and content fluctuations. According to Vaia and Liu [2], the spatial characterization of nanocomposites over six orders of magnitude is a challenge and inconsistencies are likely to appear among different techniques such as scattering spectroscopy and electron microscopy. From the structural point of view, there exist two types of nanocomposites, the intercalated one where the polymer is inserted between the silicate layers forming well-ordered multilayers and the exfoliated one where the silicate layers break into single platelets and orient themselves forming a random pattern. A detailed study of the intercalation and exfoliation behavior of clay/epoxy materials was performed by Lü et al [3]. Several studies on the mechanical behavior of clay/epoxy nanocomposites have been performed. Lan and Pinnavaia [4] reported more than a 10-fold increase in both elastic modulus and strength of an exfoliated nanocomposite co
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