Melt exfoliation in montmorillonitepolystyrene nanocomposites

Polymer clay nanocomposites (PCN) exhibit many advantages over conventional composites, while using substantially smaller quantities of filler. For various reasons, it is desirable, in nanocomposite manufacturing, to employ processes based on melt exfoliation of modified clay particles. While various researchers have studied the effects of processing variables and material properties on the effectiveness of melt exfoliation, many issues remain unresolved. This study attempts to deal with some of these. In this study an amorphous polymer, atactic polystyrene (PS), has been chosen to avoid complications related to crystallization. Three grades of (PS), having different molecular weight, were pre-blended with Cloisite® 1OA (a modified montmorillonite) in a twin-screw extruder (TSE). The TSE blends were subsequently fed to a single screw extruder, fitted with one of three specially designed attachments at the front of the screw. The attachments were designed to provide combinations of shear and elongational deformations. The resins, TSE blends, and final nanocomposites were characterized for the degree of exfoliation, mechanical properties, and rheological behavior using capillary and rotational rheometers, FTIR, XRD and TEM. The effects of molecular weight, mixing time, and levels of shear and elongational stresses, on the degree of intercalation and the properties of the nanocomposites were studied. Surprisingly, the complex and shear viscosities of the nanocomposites were found to be lower than the corresponding viscosities of the virgin polystyrene. Intercalation was achieved with in a short residence time. However, the degradation of the clay intercalant increased with residence time which causes degradation of PS