Effect of clay orientation on the tensile modulus of polypropylene-nanoclay composites

We present an experimental investigation of the effect of clay orientation, as produced by melt extrusion, on the tensile modulus of compatibilized and uncompatibilized syndiotactic polypropylene nanoclay composites. The orientation of the clay tactoids in extruded tape samples was quantified using 2D X-ray diffraction data. It was found that in the case of the tapes made from compatibilized nanocomposites the orientation of the clay tactoids increased with extrusion shear rate, while in the case of tapes extruded from uncompatibilized hybrids the clay orientation was independent of the shear rate. Tensile modulus of the extruded tapes along the flow direction was measured and was found to correlate well with the average orientation of the clay tactoids. In the case of the compatibilized hybrids the modulus increased with the extrusion shear rate until a saturation value, whereas for the uncompatibilized hybrids the modulus was nearly independent of the shear rate. Semi-quantitative predictions of the effect of clay orientation on the tensile modulus of the compatibilized tape samples were obtained using a micromechanical model