Structural Nanocomposite Bonding Reinforced by Graphite Nanofibers with Surface Treatments
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Structural Nanocomposite Bonding Reinforced by Graphite Nanofibers with Surface Treatments L. Roy Xu1, Charles M. Lukehart2, Lang Li2, Sreeparna Sengupta1 and Ping Wang1 1 Department of Civil and Environmental Engineering 2 Department of Chemistry Vanderbilt University, Nashville, TN 37235, USA ABSTRACT Graphitic carbon nanofibers were used to reinforce epoxy resin to form nanocomposite adhesive bonding. GCNFs having a herringbone atomic structure are surface-derivatized with bifunctional hexanediamine linker molecules capable of covalent binding to an epoxy matrix during thermal curing and are cut to smaller dimension using ultrasonication. Good dispersion and polymer wetting of the GCNF component is evident on the nanoscale. Tensile and shear joint strength measurements were conducted for metal-metal and polymer-polymer joints using pure epoxy and nanocomposite bonding. Very little bonding strength increase, or some bonding strength decrease, was measured. INTRODUCTION Since carbon nanotubes have extraordinary mechanical properties, they tend to be used as reinforcements in polymers and other matrices to form so-called nanocomposite materials [1-3]. Nanocomposites are a novel class of composite materials where one of the constituents has dimensions in the range between 1 and 100 nm [4]. Nanocomposite materials garner most of their material improvements from interactions at the molecular scale, influencing physical and material parameters at scales inaccessible by traditional filler materials. Wagner [5] reported that load transfer through a shear stress mechanism was seen at the molecular level. It has been reported that nanotubes increased the composite strength by as much as 25% [6]. However, multi wall nanotubes (MWNTs) are limited in their applications because of weak inter-shell interactions [7]. Single wall nanotubes (SWNTs) on the other hand are quite expensive and difficult to manufacture. Alternative reinforcement materials for nanocomposites include graphitic carbon nano-fibers (GCNFs) and graphite nanoplatelets etc [8]. GCNFs also have excellent properties and can be used as reinforcements in various kinds of matrices. They offer chemically facile sites that can be functionalized with additives thereby resulting in a strong interfacial bond with the matrix. Generally, the three main mechanisms of interfacial load transfer are micromechanical interlocking, chemical bonding and the weak van der Waals force between the matrix and the reinforcements [9]. In order to form a nanocomposite material with excellent mechanical properties, strong chemical bonding between the reinforcement and the matrix is a necessary condition, but might not be a sufficient condition. From the length-scale argument it is known that the effective toughening may not be energetically favorable at the nano length-scale [10]. This generally necessitates a filler size greater than 100 nm [11]. However, there might be significant difference in mechanical behaviors between a continuous fiber reinforced composite (e.g., carbon fib
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