Crystallization and melting behaviour of polypropylene/barium sulfate composites

The effects of polypropylene (PP)-barium, sulfate (BaSO₄) interfacial interaction on the crystallization and melting behaviour of PP/BaSO₄ composites were investigated by means of differential scanning calorimetry. The results show that BaSO₄ can act as nucleating agent and the nucleation activity increases when the PP-BaSO₄ interface is modified. Neat PP exhibits a single fusion endotherm after being non-isothermally crystallized, whereas the PP/BaSO₄ composites show dual endotherms or a broad endotherm with a shoulder at the low temperature side, indicating that there are more crystallites with less perfection formed in the composite samples. It is shown that the hindrance of BaSO₄ particles on the transport of PP chains to the crystallization zone is responsible for the formation of the less perfect crystallites. Moreover, the melting patterns of the composites are different from sample to sample, which can be attributed to the different extents of deviation from equilibrium at which the crystallization processes proceeded.