Mechanical Properties and Crystallization Behavior of Polypropylene/Nano-SiO2 Composites

In this study, polypropylene (PP)/nano-silica (nano-SiO 2 ) composites were prepared by a melt blending process. Here, a novel surface treatment method which uses combined dispersant and a coupling agent is developed to treat the nano-SiO 2 which is uniformly dispersed into the PP matrix. To treat the surface of nano-SiO 2 , the optimal content of the dispersant (SDBS) is 2.0% and the optimal amount of the coupling agent (KH-550) is 1.5%. The mechanism and synergistic effect of the combined dispersant and coupling agent are discussed based on their chemical structures. The fractography of PP/nano-SiO 2 composites after notched impact testing observed by the scanning electron microscope (SEM) proves the uniform dispersion of nano-SiO 2 in the PP phase. The mechanical testing results show that after surface treatment, both the tensile and notched impact strength of nanocomposites enhance markedly. The tensile strength reaches its maximum with the 4.0% of nano-SiO 2 and the notched impact toughness achieves its maximum with the 5.0% of nano-SiO 2 . The crystallization behavior characterized by the differential scanning calorimetry (DSC) and the crystalline structure observed by the polarizing microscope (PM) indicated that nano-SiO 2 has a nucleation role in the crystallization of PP which results in a higher crystallization temperature, a higher degree of crystallinity, and a smaller size of spherulites.