Correlation of rheology–orientation–tensile property in isotactic polypropylene/organoclay nanocomposites

Three isotactic polypropylene(iPP)/organoclay nanocomposites with changed basal resin polarity and molecular weight but fixed clay content (10 wt.%) were prepared through melt-blending. To correlate the rheological properties with the orientation behavior and tensile property in injection-molded bars, the shear response and disorientation kinetics of those molten composites were investigated through large-amplitude oscillatory shear measurements and stress relaxation experiments, respectively. Then, dynamic packing injection molding was carried out to exert oscillatory shear on the molten composites during the solidification stage, for preparation of composites with high-level orientation. The orientated structures of injection-molded bars were inspected through 2-D wide-angle X-ray scattering analysis. Our results indicated for the first time that the rheological behaviors, such as alignment induced by large-amplitude shear and stress relaxation, would be the reliable references for estimating the orientation capability of nanocomposites in practical injection-molded processing. The rheological response to shear and the disorientation kinetics play crucial roles in determining the orientation and tensile strength of molded composites.