A series of isotactic polypropylene (iPP)/calcium carbonate (CaCO 3) composites are prepared by melt blending, and the crystallisation behaviours of these composites are investigated by differential scanning calorimetry (DSC). The results show that the crystallisation exotherms displayed double peaks as the concentration of CaCO3 reaches a critical value of typically ∼8 wt-% for nano-CaCO3 and ∼20 wt-% for micron-CaCO3. With increasing content of CaCO3, the intensity of the higher temperature crystallisation peak increases, while that of the lower one decreases. Modifying the surface of CaCO3 with stearic acid leads to the increase in the critical concentration to trigger double crystallisation peaks, which is 50 wt-% for nano-CaCO3 filled iPP. The results of isothermal crystallisation, transmission electron microscopy (TEM) and polarised light optical microscope (POM) experiments indicate that the different nucleating abilities of CaCO3 composites are mainly responsible for the occurrence of the double crystallisation peaks in the composites.
- NUCLEATING ABILITY
- STEARIC ACID