(Mentor: Abbas A. Zaman, College of Engineering)
The objective of this work is to characterize the influence of clay loading and dispersion effects on the rheological properties of unsaturated polyester composites. Toughened unsaturated polyester (UPE) composites were synthesized by the blending of delaminated clay with unsaturated polyester. Rheological behavior is shown to be strongly influenced by clay loading and the extent of clay dispersion in the polymer matrix. Transition from liquid-like behavior to solid-like behavior shifts to significantly higher solids loading at higher shear rates which may be due to the alignment of the particles in the direction of flow at high shear rates. SEM micrographs are used to display the extent of intercalation and dispersion of the clay within the polymer matrix. INTRODUCTION AND BACKGROUND
Polymer/clay nanocomposites display a change in composition and structure over a nanometer length scale and have been shown to present considerable property enhancements relative to conventionally scaled composites. Layered silicates dispersed as a reinforcing phase in an engineering polymer matrix are one of the most important of such "hybrid organic-inorganic nanocomposites" . Polymer-layered silicate nanocomposites containing low levels of exfoliated clays, such as montmorillonite and vermiculite have a structure consisting of platelets with at least one dimension in the nanometer range. One of the most important features of polymeric materials is the possibility of controlling their macroscopic physical properties by tailored manipulation of their structures at a nanoscopic scale. To influence the interactions that govern the mechanical properties of polymers, specific nanoscopic scale reinforcement is efficient and beneficial. For example, montmorillonite clay provides such reinforcement through the interaction of polymer chains with the charged surfaced of clay lamellae . The use of organoclays as precursors to nanocomposite formation has been extended into various polymer systems including epoxies, polyurethanes, polyimides, nitrile rubber, polyesters, polypropylene, polystyrene and polysiloxanes, among others. Even a variety of inorganic materials, such as glass fibers, talc, calcium carbonate, and clay minerals, have been successfully used as additives or reinforcements to improve the various properties of polymers [3-10]. 1.2 Structure
The optimal properties of nanocomposites arise as the clay nanolayers are uniformly dispersed (exfoliated) in the polymer matrix, as opposed to being aggregated or phase separated as tactoids or simply intercalated. As nanolayer exfoliation becomes achieved, there is a trend in the improvement in desired properties that is manifested as an increase in tensile properties, enhancement of barrier properties, a decrease in solvent uptake, an increase in thermal stability and flame retardance, among others [11-12]. The complete dispersion of clay nanolayers in a polymer optimizes the number of available reinforcing elements for carrying an applied load and deflecting cracks. The coupling between the and the polymer matrix facilitates stress transfer to the reinforcement phase, allowing for tensile and toughening improvements. Conventional polymer-clay composites containing aggregated nanolayers tactoids ordinarily improve rigidity, but they often sacrifice strength, elongation and toughness. However, exfoliated clay nanocomposites, have to the contrary shown improvements in all aspects of their mechanical performance . 1.3 Preparation and Synthesis
The preparation of nanocomposites requires extensive delamination of the layered clay structure and complete dispersal of the resulting platelets throughout the polymer matrix. Nanocomposite synthesis by conventional polymer processing operations...