Effect of the vibration shear flow field in capillary dynamic rheometer on the crystallization behavior of polypropylene

The self-made capillary dynamic rheometer was adopted to study the relationship between the crystallization behavior of isotactic polypropylene (iPP) and the vibration shear conditions, namely, vibration amplitude and vibration frequency. The crystalline structure of iPP under different vibration conditions was characterized by using differential scanning calorimeter (DSC) and wide-angle X-ray diffractometer (WAXD) techniques. The samples extruded under vibration shear conditions had a higher melting temperature (from DSC). A new shoulder-shape peak appeared at ca. 162 °C under low frequency or low amplitude conditions, which was engulfed by the main melting peak with the increase of the vibration amplitude or frequency. This was probably an indication that more perfect crystals had formed [Polym Eng Sci 38 (1998) 1–20]. The WAXD demonstrated that crystalline form of iPP extruded was not changed but the average crystalline size decreased, according to the Scherrer formula [Analytical methods of polymer materials, China Petrochemical Press, Beijing, 1997]. This proved a large increase in the number of small crystals.