Influence of annealing on microstructure and physical properties of isotactic polypropylene/calcium carbonate composites with β-phase nucleating agent

As a part of serial work about the application of nucleating agent (NA) in polymer blends or polymer composites, a β-phase NA aryl amides compound (TMB-5) had been introduced into isotactic polypropylene/calcium carbonate (iPP/CaCO3) composites in this work. The specimens were annealed for 12 h at different temperatures (90-150 °C) and at 130 °C for different durations (3-12 h). The variations of microstructures during the annealing process were investigated using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The physical properties, including fracture toughness, stiffness and thermal properties, were measured, too. The results indicate that the decreased numbers of chain segments in amorphous region, which is easily triggered by the secondary crystallization during the annealing process, is beneficial to the improvement of toughness through promoting the lamellae to slip or elongate along the impact direction and inducing the intense plastic deformation during the fracture toughness. Further results show that improved stiffness and largely enhanced heat distortion temperature are easily achieved due to the increased fraction of crystalline component and the improved crystalline structure obtained during the annealing process. Anyway, this work proposed a simple way to achieve iPP/CaCO3 composites with high performance at very low load of CaCO3.