The Preparation Of Nano-SiO₂ Microspheres And Study On Its Application In Polyolefine

The study on inorganic particle and polymer composites becomes increasingly important in recent years. The advantages of this composite material are obvious, the performance of the material can be significantly improved simply by adding a few inorganic particles. Composite of silica/polypropylene (PP) is one of them. The surface of SiO₂ is hydrophilic and PP is hydrophobic, leading the poor compatibility between the SiO₂ and PP. The size of SiO₂ is small to nanoscale, the surface energy will be very large, leading to the reunion of the particles. Therefore, in order to effectively improve the performance of SiO₂/PP composite materials, it is necessary to improve the dispersion of SiO₂ in PP and their compatibility.The monodisperse silica microspheres were prepared by the sol-gel method in this paper. The effects of the concentrations of ammonia, amount of tetraethyl orthosilicate (TEOS), ethanol and deionized water on the size and size distribution of resulting SiO₂ microspheres were investigated in detail. The size of obtained particles could be controlled from 60 nm to 550 nm via changing reaction conditions, to meet the requirements of SiO₂ particle size under different circumstances. Polymerizable double bond was imported to surface of SiO₂ microspheres by introducing KH-570 silane coupling agent. SiO₂-P(St-EMA) nanospheres were prepared by grafted styrene (St) and ethyl methacrylate (EMA) on the surface of nano-SiO₂ with the multistage emulsion polymerization method. SiO₂-P(St-GMA) nanospheres were prepared by grafted styrene (St) and glycidyl methacrylate (GMA) on the surface of nano-SiO₂ in the same way. The composite material of SiO₂-P(St-EMA) nanospheres and polypropylene (PP) were prepared by the melt-blending process, the mechanical and crystallization properties were investigated. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and Zeta PALS zeta potential analyer were used to characterize the structure, morphology, surface coating and the particle size and distribution of SiO₂ before and after modification. Differential scanning calorimeter (DSC) and SEM were used to characterize Crystalline properties and fracture surface of the composites. The results demonstrated that the obtained SiO₂ microspheres were spherical with monodispersion. Hydrophobic polymer chains had been successfully grafted to surface of silica microspheres. SiO₂-P(St-GMA) and SiO₂-P(St-EMA) nanospheres had a structure of sphericity composed of SiO₂ as core, P(St-GMA) and P(St-EMA) as shell respectively and it improved the dispersion obviously. The impact and tensile strength of SiO₂-P(St-EMA)/PP were improved significantly when the loading of SiO₂-P(St-EMA) was as low as 1% to 2%, and the heterogeneous nucleation effect of nano-SiO₂ increased the crystallization temperature and melting temperature.