Orientated crystallization in discontinuous aramid fiber/isotactic polypropylene composites under shear flow conditions

Melt blends of short aramid fibers (AF) and isotactic polypropylene (iPP) are subjected to shear at 145°C and the structural evolution and final morphology are examined by in situ synchrotron X-ray scattering/diffraction and high-resolution scanning electron microscopy, respectively. The results indicate that the presence of short AFs significantly enhances the crystallization of iPP. It is argued that shear flow in this system exerts a twofold orientating action, namely, on the bulk iPP molecules and on the short AFs. The resultant crystalline morphology reflects the combined effects of crystallization on orientated iPP molecules to facilitate a shish kebab morphology and at the interface of the aligned fibers, to form transcrystallinity.