Effects of nanoparticle treatment on the crystallization behavior and mechanical properties of polypropylene/calcium carbonate nanocomposites

Effects of nanoparticle surface treatment on the crystallization behavior and mechanical properties of polypropylene (PP)/CaCO₃ nanocomposites were investigated by using differential scanning calorimetry (DSC), polarized optical microscope (POM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results demonstrated that the interfacial interaction formed between PP and nanoparticles significantly influenced the thermal and mechanical properties of nanocomposites. It was found that CaCO₃ nanoparticles modified by a single aluminate coupling agent (CA-1) could improve the onset crystallization temperature more effectively than that modified by a compound surface-treating agent (CA-2) could. However, there is no significant difference in total rate of crystallization for the two PP/CaCO₃ nanocomposites (PPC-1 and PPC-2), which contained CA-1 and CA-2, respectively. In contrast, CA-2 modified nanoparticles could cause smaller spherulites and induce much more β-phase crystal in nanocomposites than that of CA-1 modified nanoparticles. This may be explained by a synergistic effect of aluminate coupling agent and stearic acid in CA-2, which also resulted in an improved toughness for PPC-2.