Hybrid epoxy nanocomposites: lightweight materials for structural applications

Abstract

The processing parameters, namely, clay loading, magnetic stirring time and sonication time, were optimized for the dispersion of two types of clay into an epoxy and into chopped strand mat (CSM) glass fiber-based epoxy nanocomposite laminates. A vacuum-assisted resin transfer molding setup was used to fabricate these laminates. Optimizations were performed based on improvements in Young's modulus. The intercalated and exfoliated distributions of clay in the composites were confirmed using X-ray diffraction and transmission electron microscopy. The transmission electron micrographs of optimized specimens showed a well-ordered intercalated structure within the epoxy. Using optimized processing conditions, three layered laminates of CSM, woven roving glass fibers or both were prepared with epoxy and clay for the preparation of new lightweight hybrid epoxy nanocomposites. The tensile, flexural and impact properties of these hybrid nanocomposites were investigated. A combination of the two types of glass fibers produced promising results. Polymer Journal (2012) 44, 334-339; doi:10.1038/pj.2011.140; published online 18 January 2012Keywords: clay; epoxy; exfoliation; hybrid epoxy nanocomposites; intercalation INTRODUCTIONEpoxies are generally used in structural applications. Epoxy-based plastics provide extraordinary mechanical properties, including good dimensional stability, minimal water absorption, and chemical and corrosion resistance. 1 Within the past two decades, nanoparticles have been utilized to enhance the mechanical properties of available plastics. 2 Enhancements have come about in the form of high-specific moduli and increased specific strength. Toyota Research Labs first introduced clay into a Nylon 6 resin for seat belts, and an improvement in the thermomechanical properties 3-5 was observed. Clays (layered silicates) are commonly used to make polymer nanocomposites; these belong to a structural family known as the 2:1 layered clays or phyllosilicates. Montmorillonite clay consists of several hundreds of individual nanoscale layers held together by electrostatic forces. It is the most commonly used layered silicate 6 clay. The clay particles exhibit high strength and stiffness along their lengths as compared with glass fibers, 7 and they have a high aspect ratio, thus providing a large surface area for contact with polymers. 8 These particles are in the form of platelets that are 0.96 nm thick and 250 nm in both length and width. 8 The homogeneous dispersion of clay into polymers is a challenging task. Previous studies suggest that three forms of structural morphologies may be obtained after dispersion of clay into a polymer, including intercalation, exfoliation and phase-separated structures. 9-14 Unidirectional glass fiber epoxy laminates are used for structural applications because of their high-specific strength

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