Study On In-Situ Polymerization Of Propylen With Nano-CaCO₃ And The Properties Of Resulting Composites

In situ polymerization of propylene with nano-CaCO3 and the chief properties of the products was studied. By select of the polymerization methods of PP, the liquid mass polymerization method, little mass polymerization method, which is fitted for the study was selected. The methods of surface modification for nano particles and its put in the polymerization kettle was studied, it's shows by the mass polymerization process in the kettle of 12 cubic meter, the disperse of the nano particles is well-proportioned, and the physical properties and the thermal behavior of the composites increased significantly, especially the impact strength and the rupture elongation of the composites. Nano-CaCO3 particles don't affect the polymerization at the low concentration but the polymerization velocity is decreased at the concentration of nano -CaCO3 particles more than 3%. PP/CaCO3 nano-composites were prepared also by melt-blending method ,The properties and the dispersion of nano-CaCO3 of composites prepared by different method were investigated and compared by means of Scanning electron microscopy (SEM),Transmission electron microscopy(TEM) and mechanical properties test. The results shows the overall properties of pp/ nano-CaCO3 composites prepared by in situ method is proximity to melt-blending method, and there are superiorities on technology processes to the former. The uniform speed crystalline at varied content of nano-CaCO3 and the nonisothermal crystallization kinetics of polypropylene/nano-CaCO3 composite, which was prepared by in-situ polymerization, was studied by means of Differential Scanning Calorimetry(DSC). The modified Avrami theories of Ozawa and Mo were used to analyze the data of DSC. It shows that the faster of the cooling rate, the higher of the crystallinity at the unit crystallization time. And the crystallization mode has not significant change. It's also show that nano-CaCO3 particles can be used as nucleating agent during non-isothermal crystallization process of PP. Characteristics and crystal structure of polypropylene/nano-CaCO3 composites with varied content of nano-CaCO3 are studied and observed by Polarizing Microscope also. The results show that nano-CaCO3 acts as a nucleation agent in PP and heterogeneous nucleation domains during the crystallization, thus upgrading the crystal temperature and nucleation rate, the spherulites of the crystal become small. The study of the effect by varied content of nano-CaCO3 to crystallization show, when the content of nano-CaCO3 is 2.5-3%,the influence to the above characteristics is prominent.The rheological behavior of PP/nano-CaCO3 In-situ composites was investigated using capillarity rheometer. The results show that the apparent viscosity of the composite decreased with the increase of the shear rate, but it is not sensitive to temperature; When the content of nano- CaCO3 is above 3%, the apparent viscosity decreased obviously with the increaseing of the content of nano-CaCO3; The flow activiation energies is higher than others when the content of nanoparticles is about 3%, and the sensitivity of the shear rate to temperature is relatively higher than others also.