Mechanical Properties of Chemically Functionalized Clay Vinyl Ester Nanocomposites
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Mechanical Properties of Chemically Functionalized Clay Vinyl Ester Nanocomposites S. Balakrishnan and D. Raghavan Polymer Group, Department of Chemistry, Howard University, Washington DC 20059. ABSTRACT This study focuses on the role of chemistry of onium salt(s) used in functionalizing clay and the processing conditions in achieving exfoliated clay vinyl ester nanocomposites. Two different clay treatments were added to vinyl ester resin and three different processing conditions were examined in the formulation of nanocomposite. Through this study, we demonstrate that the degree of exfoliation and dispersion of layered silicate nanocomposite is affected by both processing and the clay chemical treatment. At an organoclay loading of only 3.5wt%, the modulus improved by 20% in partially reactive organoclay system, while the modulus improved by 10% in nonreactive organoclay system compared to that of pristine vinyl ester resin. INTRODUCTION Vinyl ester resins are currently used as matrix material in glass fiber reinforced composites (GFRP), for use in the construction and repair of bridges and other civilian structures. Despite the positive attributes of GFRP, the use is currently limited due to durability concerns of the composite. It has been shown that atmospheric moisture can diffuse in to the resin/fiber interface layer and cause fiber weakening. Nanocomposites offer an interesting alternative for reducing the moisture ingress in to the polymeric composite (1). In addition, improvements in flammability and mechanical properties of clay filled polymeric nanocomposites relative to unfilled polymer can also be achieved. Nanocomposites garner most of their properties improvement from molecular interactions of clay and polymer and the final morphology of nanocomposites. The synthesis of high performance nanocomposites involves dispersion of clay in a polymeric matrix. Commonly, clay sheet separation is achieved by replacement of the cations of the clay layer by organoammonium cations and swelling the organoclay in monomer before the addition of curing agent. Many articles focus on the importance of the chemistry in modifying the clay surface, less emphasis is given to the role of processing parameters on the final nanocomposites morphology. While there are reports that explore the importance of processing conditions to make exfoliated nanocomposite from a thermoplastic, limited work has been done to investigate the importance of processing parameters on exfoliated thermoset nanocomposite (2-4). In this study, we show that the details of the processing can be as important as the choice of organic treatment in influencing the degree of dispersion of the MMT in the polymer matrix. Materials and Methods: Details of non-reactive surfactants (undecyl amine hydrochloride and octadecyl amine hydrochloride), and the reactive surfactants (ω-undecylenyl amine hydrochloride and C19 amine hydrochloride) used in this work can be found elsewhere (5,6). The preparation of organoclay was performed by the substitution of catio
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