Unusual hierarchical structures of mini-injection molded isotactic polypropylene/ultrahigh molecular weight polyethylene blends

The introduction of ultrahigh molecular weight polyethylene (UHMWPE) leads to very rich and unusual hierarchical crystalline morphologies in mini-injection molded isotactic polypropylene (iPP) based materials and the role of UHMWPE in the formation of the hierarchical structures has been studied. The hierarchical structures, including the shish-kebab-like structure, β-cylindrite, β-spherulite and α-spherulite, in the injection molded samples were characterized by wide-angle X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Results indicated that the content of crystal modifications and the distribution of the crystal morphologies formed are closely related to the density and arrangement of the row nuclei formed, which can be tuned by the content of UHMWPE and its dispersion in the matrix. The density and arrangement of the row nuclei are determined by the hydrodynamic interaction, melt adsorption, and interdiffusion between iPP and UHMWPE. With the distance between the row nuclei increasing, the corresponding dominating crystals are shish-kebab-like structure, β-cylindrite, β-spherulite and α-spherulite in sequence.