Isotactic polypropylene reinforced atactic polypropylene by formation of shish-kebab superstructure

To make large scale, effective use of atactic polypropylene (aPP), normally regarded as industry waste, isotactic polypropylene (iPP) was blended with aPP with a guiding ideology of structuring processing. Herein, the aPP/iPP blends were melt processed through modified injection molding, i.e., oscillation shear injection molding (OSIM), in which an oscillation shear flow field was applied to induce self-reinforcing oriented iPP crystals. With addition of only 30 wt% iPP, the tensile strength of the blend could increase from 1.6 MPa for neat aPP to 26.6 MPa, which is comparable to that of conventionally injection molded high density polyethylene. Further increasing iPP content to 50 wt%, the tensile strength of OSIM aPP/iPP sample rose up to 41.6 MPa, already higher than those of industrial-scale extruded and injection-molded iPP. The results of wide-angle X-ray diffraction (WAXD), small-angle Xray scattering (SAXS), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) testified that the increased enhancement of mechanical performance of OSIM blend with the increase of iPP content can be ascribed to the progressive formation of iPP shish-kebab networks. It is a mechanism to reinforce amorphous polymer under shear flow by adding crystalline component. Meanwhile, adding iPP into aPP could effectively enhance the viscosity of aPP and hence the processability of aPP could be significantly improved. This technique opens a gate to manufacture aPP into practical products through the most common processing methods like extrusion and injection-molding. (C) 2015 Elsevier Ltd. All rights reserved.