Rheological and Thermal Behaviour of Different Molecular Structure Polypropylene Blends

High melt strength/block polypropylene (HMSPP/PPB) blends and high melt strength/random polypropylene (HMSPP/PPR) blends were prepared by a twin-screw extruder to decrease the high stiffness of polypropylene and to improve its impact strength. Rheological properties of the two blends were investigated using a rotational rheometer. The complex viscosity and storage modulus data at low frequency region indicated that the melt elasticity and melt strength of the blends were affected by varying the content of PPB and PPR in the blends. Moreover, the melt strength of HMSPP/PPR blends was better than that of HMSPP/PPB. The non-isothermal crystallization behaviour of the blends was studied using differential scanning calorimetry with various cooling rates and was analyzed by the Avrami method. It was found that the melt and crystallization temperatures of the blends increased with the ratio of PPR and PPB. PPB also changed the crystallization process of the blends, leading to smaller spherulite size and more spherulites, but PPR only slightly affected the crystal behaviour.