Study On PP Toughened And Reinforced With Nano-SiO₂

The research on the polypropylene (PP) modified with nano-sized SiO2 has been attended extensively. But the dispersion of the nano-sized CaCO3 in PVC is not good enough by the surface treatment and the extruding technology used now. And studies on the reinforcement and toughing mechanism are not intensive enough.In this thesis two kinds of coupling agents and maleic anhydride (MAH) grafted polypropylene (PP-g-MAH) were employed to act as interface compatibilizers for PP/nano-SiO2. Master batches from PP (90), nano-SiO2 (10) and coupling agent (1) were prepared by twin-screw extruder firstly. The composites with different compatibilizers and nano-SiO2 content were characterized by means of mechanical testing, Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Fourier transformation infra-red spectroscopy (FT-IR), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), etc. The relation between the structure and property of the composites was discussed in this thesis.The results showed that PP filled with nano-SiO2 modified with different interface compatibilizers had better mechanical performances than pure PP. The mechanical properties of the PP/nano-SiO2 modified with silicone coupling agent and PP-g-MAH was better than that of PP/nano-SiO2 modified with solo coupling agent. We also found that there is some furthest dosage of nano-SiO₂ in PP/nano-SiO2. The Izod impact strength was increased 48% and the tensile strength was increased 12% contrast with pure PP, achieved the highest value when 3% nano-SiO2 by weight modified with silicone coupling agent and PP-g-MAH was added.XRD and DSC were used to investigate the surface treatment and the content of the nano-SiO2 influencing their crystalline characteristic. Results showed that PP/nano-SiO2 had the same crystal type with pure PP. So the melt point changed a little. nano-SiO2 acted as the nucleation agent in PP, and greatly upgrading the crystal temperature, nucleation rate and crystallinity when 1%⁵% nano-SiO2 by weight was added.Through the research on the crystallite of the composites modified with silicone coupling agent and PP-g-MAH, Research showed that the size of the crystallite and oriented crystallization had obviously influence on the mechanical performances.The SEM results showed that nano-SiO2 was dispersed well in PP, which promoted the matrix undergo shear yielding rather than brittle fracture.